Fork offsets 38-51mm or more and Head Angle issues, let's get it sorted out.- Mtbr.com
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  1. #1
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    Caution;  Merge;  Workers Ahead! Fork offsets 38-51mm or more and Head Angle issues, let's get it sorted out.

    Hello

    Basing on this http://g-tedproductions.blogspot.com...angle-for.html
    and
    http://www.kreuzotter.de/deutsch/lenk.htm
    We are able to calculate ground contact patch for a given fork offset and wheels size.
    Let us see the steeper the HA is and the more offset we have the smaller the contact patch is.
    The slacker the HA and less offset we have the more contact patch we get.
    The steeper the HA is the less offset we need to get the same contact patch with slacker HA and longer offset.
    Thus slack angles + long offset will improve the handling - less contact patch, but longer wheel base - the whole bicycle is long and unpractical in tight switchbacks.
    Until now everything is intuitive and common. Here comes an example of Spider 29" which is reported with 73' HA (or any other 29" bike in the future) to be ready to pitch you over the bars more likely than other with slacker HA. Of course we get the steereability of 26er, but DH section must be tackled with your butt going farther behind the saddle.

    - My question is what would happen with Spider 29" DH inappropriateness if we get Reba with 43mm or 51mm offset instead of 38mm. Will that much offset make it harder to endo on DH sections or the bike will get too twichy and will be swayed from side to side like 26er on uphills (the front wheel fiddling)
    If we got Reba with 35, 32, 30mm offset, accordingly this would make more contact patch but how would it affect DH section on our mentioned Spider 29"?

  2. #2
    Law
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    Quote Originally Posted by Davidcopperfield
    We are able to calculate ground contact patch for a given fork offset and wheels size.
    Let us see the steeper the HA is and the more offset we have the smaller the contact patch is.
    The slacker the HA and less offset we have the more contact patch we get.
    The steeper the HA is the less offset we need to get the same contact patch with slacker HA and longer offset.
    Thus slack angles + long offset will improve the handling - less contact patch, but longer wheel base - the whole bicycle is long and unpractical in tight switchbacks.

    When I read this I just shook my head. You really don't know what you are talking about. I for sure don't know what you are talking about. "Contact Patch" does not change depending upon the head angle and offset as far as I can figure.

    You might be better off putting you thoughts into something more productive, like looking for porn on the web or something.

  3. #3
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    The contact patch size stays the same no matter the head angle / off-set, it is purely dependant on wheel diameter and tyre width.

    The part that changes is the centre of the contact patch in relation to the steering axis...kind of like the "trail" on a shopping trolly wheel that keeps it pointing the direction of travel when you push the trolly forward.

    The bigger the trail (slack HA or small off-set) gives a more stable steering. A steeper HA and/or larger off-set on the forks moves the contact patch nearer the steering axis making the steering handling "faster" and more "twitchy"

    Hope this helps,

    Alex
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  4. #4
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    You might be better off putting you thoughts into something more productive, like looking for porn on the web or something.
    or maybe actually buying and riding a real 29er, which as far as i can tell he still hasn't.

    this guy is too dumb to even consider as a troll...
    what would rainbow unicorn do?

  5. #5
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    Contact patch will not change. Maybe you used the wrong words. The larger fork offset will increase the wheelbase which will help in the downhill sections of course. Also, on DH sections the 29" wheels hold more centrifical force adding to its stability. So it will still "FEEL" and "BE" more stable that a 26er. A change in fork offset will not be that big of a deal for the Spider. Not sure what long wheelbase quick turning bikes are out there.

    But from what I can get, fork offset is all about feel. And if you know how to ride then it would not matter. Getting ready to fly over the bars is a little much. If anything, the stability will increase.

  6. #6
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    IMO the centrifical force only really holds true for something when the wheels are not touvhing the trail. Different attack angle of various wheel size deflect differently when coming in contact with trail objects, I think THAT's what does the trick for 29" wen going DH.

    Longer doesn't have to be badder. A really short front end for instance will have you endo the moment you feather the front brake when going down anything steep, or having the rear roll over a little marble on the trail.

  7. #7
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    I'm honestly a little surprised that this guy hasn't been silenced/banned yet. Holy crap.
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  8. #8
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    It's obvious (good God, I hope) that you're not really talking about contact patch, because that has absolutely nothing to do with the geometry of the bike. Are you talking about trail? It almost sounds like it, although even then the original post doesn't quite make sense.

    It's possible the original post could turn into a question that made sense. David, do you want to clarify what you're talking about (obviously not regarding contact patch, again I hope) and try asking again?
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  9. #9
    SyT
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    Quote Originally Posted by GlowBoy
    .

    It's possible the original post could turn into a question that made sense. David, do you want to clarify what you're talking about (obviously not regarding contact patch, again I hope) and try asking again?

    For the love of all that is holy, stop casting the chum. Can't keep the boy outa the nets as it is.....

  10. #10
    keholio
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    Several things can effect tire contact patch size and make it bigger.
    Moving from 38mm to 51mm tire can make the contact patch bigger.
    Moving from 51 to 38 PSI in the tires makes the contact patch bigger
    Increasing rider weight by 51 Kgs makes the contact patch bigger (my normal winter weight gain after cross season ends.)
    But, moving from 38 to 51 mm offset has no effect on tire contact patch.
    Agree with Cloxxki short front end is a contributing factor for endo tendancies of the bike. From my experience I can say other contributing factors are:
    Higher center of gravity
    fork brake dive
    poor brake modulation
    having a passanger ride on the handlebars down big drops
    poor line choice
    wrong sized bike
    riding in an altered state
    Chain suck
    getting in over my head on tech terrain
    my favorite in Fruita, "look, no hands"

    However, this said, My Karate Monkey which is very short on the wheelbase is a very capable descender for what it is. The bike handles steep technical terrain very well, not as well as a DH rig but it still gets the job done.

  11. #11
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    Quote Originally Posted by Keholio
    Increasing rider weight by 51 Kgs makes the contact patch bigger (my normal winter weight gain after cross season ends.)
    You put on 51kg over the winter? Are you Jan Ulrich by any chance?

  12. #12
    keholio
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    No Jan here,
    Likewise I can be found in those long dark winter months perfecting my donut eating skills. My wife says she can hardly tell . . .

  13. #13
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    So if I had a bike that was already pretty long in the wheelbase, more trail makes it even longer? and that would be better for downhills but worse for climbing, faster handling?
    ROTOR HEAD

  14. #14
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    The new fork offset moves the top of the fork legs forward but the bottom of the legs stay in the same place. In other words, it steepens the fork legs.
    It does not change the wheelbase and I can't see how it could affect the contact patch.
    The effect of the new offset is the reduction of trail.
    Before the new offset 29ers resorted to steeper HTAs to reduce trail.
    Now that the new offset is here you will see bike makers slackening the HTAs.
    A case in point is the Monocog Flight 29er versus the Monocog 29er.
    The Flight has a 71 degree HTA, the Monocog a 72 degree HTA.
    The design of the Flight took into account the advent of the new offset.
    The Monocog is a "first wave" 29er, designed when the new offset was not on the horizon.
    Trail is trail, it doesn't matter how you achieve it, whether you use steeper HTAs or more fork offset.
    The advantage of slacker HTAs with more offset is less toe overlap, a possible problem in the smaller frame sizes. I have no problem on my size large frame with a 72 degree HTA and the old fork offset and size 12 feet.
    I have the impression that putting a fork with the new offset on a first wave 29er with a HTA of 72 degrees or greater is NOT a good idea. I think it would make the front end too steep. Not good on steep technical downhill. It might be OK with a rigid fork but I think it would be a disaster with a suspension fork.
    Some people would like it but I think most people would hate it.
    A Spider 29er with it's 73 degree HTA is already too steep with the old fork offset. It would be ridiculously steep with a fork with the new offset.
    Ironically, early 29er makers who, perhaps naively, spec'd a HTA of 71 degrees or less will be OK with the new offset. Those are the bikes that gave 29ers the unkillable reputation for steering slowly.
    Fortunately, it looks as though fork manufacturers are going to be offering forks in both the new and the old offsets, at least for the time being. The old offset will probably be phased out.
    If you have a "first wave" 29er with a HTA of 72 degrees or more and you like it the way it is make sure you buy a fork with the old offset.

  15. #15
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    Most of what you said is accurate except for the first two sentences. More rake = the dropouts further away from the center line of the steerer.
    So as you would say, the tops stay in same place but the dropouts move forward. Making the fork legs slacker in angle.

    As to what DC is talking about, I have no idea.


    jw


    Quote Originally Posted by GeoKrpan
    The new fork offset moves the top of the fork legs forward but the bottom of the legs stay in the same place. In other words, it steepens the fork legs.
    -

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  16. #16
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    So with my new frame (HTA 70.7) getting a WB fork with 43mm offset and large travel 135mm (slackening the HTA more), would be a good thing I think.
    ROTOR HEAD

  17. #17
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    Hold on there a minute!

    Quote Originally Posted by GeoKrpan
    The new fork offset moves the top of the fork legs forward but the bottom of the legs stay in the same place. In other words, it steepens the fork legs.
    It does not change the wheelbase and I can't see how it could affect the contact patch.
    This is erroneous. The off set is achieved in the crown in most fork designs, but it can also be acheived by "off setting" the drop outs from the steering axis. Check out an old first generation Manitou fork for a good example of what I'm talking about. So, to correct the statement here that you made, the axle is off set from the steering axis to achieve whatever specified off set is desired. How you manage to do this can be by off setting the crown, the drop outs, or a combination of the two. As you can see, this certainly affects the wheelbase.

    The effect of the new offset is the reduction of trail.
    Before the new offset 29ers resorted to steeper HTAs to reduce trail.
    Yes, this is correct.

    Now that the new offset is here you will see bike makers slackening the HTAs.
    A case in point is the Monocog Flight 29er versus the Monocog 29er.
    The Flight has a 71 degree HTA, the Monocog a 72 degree HTA.
    The design of the Flight took into account the advent of the new offset.
    The Monocog is a "first wave" 29er, designed when the new offset was not on the horizon.
    Trail is trail, it doesn't matter how you achieve it, whether you use steeper HTAs or more fork offset.
    Yes, trail is trail, but you can achieve it with a combination of factors.

    The advantage of slacker HTAs with more offset is less toe overlap, a possible problem in the smaller frame sizes. I have no problem on my size large frame with a 72 degree HTA and the old fork offset and size 12 feet.
    You are right. Toe overlap is a problem with smaller sizes. This new crop of longer offset forks will allow for even smaller sized 29"ers with suspension forks to be produced without toe overlap problems.


    I have the impression that putting a fork with the new offset on a first wave 29er with a HTA of 72 degrees or greater is NOT a good idea. I think it would make the front end too steep. Not good on steep technical downhill. It might be OK with a rigid fork but I think it would be a disaster with a suspension fork.
    Some people would like it but I think most people would hate it.
    Maybe. Possibly, but some folks might really dig it. Witness the three or four different offsets for road racing bikes. To each their own.

    A Spider 29er with it's 73 degree HTA is already too steep with the old fork offset. It would be ridiculously steep with a fork with the new offset.
    "Rediculously quick", perhaps, but steepness, (in referance to head angle) should remain the same, given the assumption that we are working with the same axle to crown measurements across the board. (Axle to crown can affect head tube angle and thus trail)

    Ironically, early 29er makers who, perhaps naively, spec'd a HTA of 71 degrees or less will be OK with the new offset. Those are the bikes that gave 29ers the unkillable reputation for steering slowly.
    Fortunately, it looks as though fork manufacturers are going to be offering forks in both the new and the old offsets, at least for the time being. The old offset will probably be phased out.
    If you have a "first wave" 29er with a HTA of 72 degrees or more and you like it the way it is make sure you buy a fork with the old offset.
    Yes, for the time being you will be able to "tune" your handling to your liking with different offsets in suspension forks, just like we have been able to do with rigid forks for a few years now.
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  18. #18
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    What is a "good thing"?

    Quote Originally Posted by IBIKEAZ
    So with my new frame (HTA 70.7) getting a WB fork with 43mm offset and large travel 135mm (slackening the HTA more), would be a good thing I think.
    It depends on your desired result.

    It sounds as though your handling would remain very similar to what you have now with the changes you detail. If that's "a good thing", then you will be happy, I guess.
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  19. #19
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    so for reference sake:


    What is this "new offset" and what was the "old offset"? (sorry for the questions but I am new to this stuff...again)

    and less trail is a good thing(?) How so?
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  20. #20
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    Quote Originally Posted by rockcrusher
    so for reference sake:


    What is this "new offset" and what was the "old offset"? (sorry for the questions but I am new to this stuff...again)
    "Old off set" was determined from 26"ers "ideal" XC offset of 38mm-40mm. The suspension companies had to make a huge investment in tooling and manufacturing to set up the new off sets, so they waited until this crazy 29"er thing looked like money before they invested. The "old" off sets on 29"er forks was a band aid to get 29"er suspension out on the market to satisfy the needs of the early adopters of the format. Although the Marz forks on early Fishers were 43mm, if I'm not mistaken.

    and less trail is a good thing(?) How so?
    Going from 26 inch wheels to 29 inch wheels automatically increases the trail measurement, so the first 29"ers adapted by increasing the head angle a bit to compensate for sluggish handling. This was only mildly acceptable to most single track fiends, since 29"ers were still not as snappy as their 26"er cousins in the handling department.

    We have since seen some bikes go to a steeper head angle (73 degrees ) to get that 26"er feel and now with the new off sets we will gain back more quickness since a lower trail figure increases the "quickness" of the front end, while a higher trail figure usually is said to be "slow" handling, or more stable.

    If you use the analogy of the shopping cart wheel, you can see that if the wheel "trails" the steering axis by a greater distance, the cart will be harder to turn, while if the distance is shorter to the point that the wheel is barely behind the steering axis the cart wheel wobbles nervously and the cart becomes more unstable, harder to hold in a straight line, than before. Somewhere in the middle is a happy medium.
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  21. #21
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    I'm just getting the frame next week. I meant "good thing" to good handling, stable.

    Quote Originally Posted by Guitar Ted
    It depends on your desired result.

    It sounds as though your handling would remain very similar to what you have now with the changes you detail. If that's "a good thing", then you will be happy, I guess.
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  22. #22
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    Ahhh so more offset plus shallower HA = quick handling and less trail.

    So confusing. Now I remember why it sucked before suspension the first time when you had to navigate through offsets and trail. Suspension manufacturers locked us into those old trail numbers and for years I didn't care. Now with a 29er frame sitting in my living room I have to care again. Understanding trail/offset/HA is like reading the OP's posts.

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  23. #23
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    Ted, love it when you come out swingin' .
    Are there any fork makers who are currently achieving the new offset by a means other than altering the crown?

    My opinion reflects my personal tastes, lack of abilities, and local riding conditions. I live at the foot of some of the steepest mountains in the world. It's steep up or steep down, very little in between. You gotsta' get back. Thus my paranoia of overly steep angles. They don't seem to faze some people but I'm not one of them. Forks with adjustable travel or ETA are a good idee-er here.
    Did you read the full suspension 29er shootout on MTBR? Their opinion of the Spider was no surprise to me given it's 73 degree HTA.

  24. #24
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    Quote Originally Posted by Guitar Ted
    Yes, for the time being you will be able to "tune" your handling to your liking with different offsets in suspension forks, just like we have been able to do with rigid forks for a few years now.
    How about a fork with this type of dropouts?
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  25. #25
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    Quote Originally Posted by Davidcopperfield
    Hello

    Basing on this https://g-tedproductions.blogspot.co...angle-for.html
    and
    https://www.kreuzotter.de/deutsch/lenk.htm
    We are able to calculate ground contact patch for a given fork offset and wheels size.
    Let us see the steeper the HA is and the more offset we have the smaller the contact patch is.
    The slacker the HA and less offset we have the more contact patch we get.
    The steeper the HA is the less offset we need to get the same contact patch with slacker HA and longer offset.
    Thus slack angles + long offset will improve the handling - less contact patch, but longer wheel base - the whole bicycle is long and unpractical in tight switchbacks.
    Until now everything is intuitive and common. Here comes an example of Spider 29" which is reported with 73' HA (or any other 29" bike in the future) to be ready to pitch you over the bars more likely than other with slacker HA. Of course we get the steereability of 26er, but DH section must be tackled with your butt going farther behind the saddle.

    - My question is what would happen with Spider 29" DH inappropriateness if we get Reba with 43mm or 51mm offset instead of 38mm. Will that much offset make it harder to endo on DH sections or the bike will get too twichy and will be swayed from side to side like 26er on uphills (the front wheel fiddling)
    If we got Reba with 35, 32, 30mm offset, accordingly this would make more contact patch but how would it affect DH section on our mentioned Spider 29"?
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  26. #26
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    Quote Originally Posted by GeoKrpan
    Ted, love it when you come out swingin' .
    Are there any fork makers who are currently achieving the new offset by a means other than altering the crown?
    Nope. Crown offset means that you don't have to make new lowers with a totally different design which would negatively affect the way the sliders operate in the lowers. "Leading axle" designs tend to bind more. So the crown redesign is more desirable.

    My opinion reflects my personal tastes, lack of abilities, and local riding conditions. I live at the foot of some of the steepest mountains in the world. It's steep up or steep down, very little in between. You gotsta' get back. Thus my paranoia of overly steep angles. They don't seem to faze some people but I'm not one of them. Forks with adjustable travel or ETA are a good idee-er here.
    Did you read the full suspension 29er shootout on MTBR? Their opinion of the Spider was no surprise to me given it's 73 degree HTA.
    I here ya on the steep terrain stuff. I can definitely see where that sketchy front end/front center would be a scary thing in that sort of terrain.

    I did read the reviews, but I didn't get a whole lot out of them, since the focus was so haphazard that getting ahold of how things compared was almost impossible.
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  27. #27
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    Ahhh! You're going to the "Way Back Machine"!

    Quote Originally Posted by grawbass
    How about a fork with this type of dropouts?
    That's a GT fork. I remember those!

    Anyone remember the fork that Walt Wehner made with the adjustable rake? That would definitely be a pertinent thread to dredge up here as Walt tried it all and gave a good rundown of a useable trail range for 29"ers back then.
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  28. #28
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    New question here.

    Quote Originally Posted by rockcrusher
    Ahhh so more offset plus shallower HA = quick handling and less trail.
    In conclusion, coming back to Spider 29" if shorter offset 32mm or 30mm Reba was made (aside from it, exactly the same) the nimbleness of Spider 29" would be slower but more stable and harder to endo on DH sections?
    Thus less offset plus steeper HA= slower handling and more trail and more stable?

  29. #29
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    Mister Copperfield - what sort of bicycle do you own? How many 29ers have you owned? Stop avoiding the question. Your credibility is suffering.

  30. #30

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    Whatta pack of A$$HOLES!!!!

    I think all the guy is asking is if the new 51mm offset fork will make bike like the Spider with a 73* HTA so twitchy that they will be unbearable on downhills and consequently make 29ers with 70.5* head angles handle similarly to 29ers with 72* and 38mm offset forks.

    Jeez, Tina

  31. #31
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    I hope you are kidding.

    Quote Originally Posted by VERVE 29er
    Whatta pack of A$$HOLES!!!!

    Jeez, Tina
    One thing I can say, if, and hopefully when DC finally does score a 29er, he's gonna have it all sorted out. I think he has to be running out of questions. Maybe he will start "shopping" for a DH bike or something.

  32. #32
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    New question here.

    Quote Originally Posted by VERVE 29er
    I think all the guy is asking is if the new 51mm offset fork will make bike like the Spider with a 73* HTA so twitchy that they will be unbearable on downhills and consequently make 29ers with 70.5* head angles handle similarly to 29ers with 72* and 38mm offset forks.

    Jeez, Tina
    You knocked the nail on the head, however another problem appears with slacker HA and longer offset- the wheelbase is longer in comparison with steeper HA and smaller offset, right?
    Slacker HA puts the wheel more up front, whereas steeper HA tucks it under, therefore shortens the wheelbase. To keep the wheelbase short and manoeuvrability acceptable/comparable to 26er it is neccessary to keep steep HA and shorter offset?
    In the long run this poses difficulty in building any frame under 18"/17,5" and eventually longer wheelbase with slacker HA and longer offset win.
    Am I correct or did I miss something?

  33. #33
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    Quote Originally Posted by Davidcopperfield
    To keep the wheelbase short and manoeuvrability acceptable/comparable to 26er it is neccessary to keep steep HA and shorter offset?
    No. You can keep the wheelbase equal by shortening the toptube.
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  34. #34
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    The key thing here is keeping the fork trail the same.
    A "first wave" 29er will ride just like a "new wave" 29er if the fork trail is the same.
    The top tubes can be identical.
    The "new wave" 29er will have a slacker HTA but a steeper fork.
    The "first wave" 29er has a steeper HTA but a slacker fork.
    They will handle the same if the fork trail is the same. Trail is trail no matter how you arrive at it.
    The advantage of a "new wave" 29er is less chance of a toe overlap problem and that in the future the new offset will be the only one available.
    The advantage of a "first wave" 29er is that they are available NOW and there's no disadvantage unless you need a small frame size. The old fork offset should be around long enough for you to get your money's worth out of it.
    I wouldn't get a Spider. Read the MTBR full suspension 29er shootout.

  35. #35
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    David - look for a different bike. I rode a Spider for several months. And yes the H.T angle is steep. It is great for XC riding. Not great for down hill riding. Whenever I was going down really steep sections "it was not ideal"
    You can't fix what you are trying to fix with a fork that doesn't even exist.
    Just get a RIP 9 and put a White Brothers fork on it and be content with the best set up currently available.
    If this doesn't work then buy a nice hard tail 29er for the XC stuff and buy a decent downhill bike for the down hill stuff.
    Then you can have a 29er and you can put whatever fork your current mood demands on the 26er.
    Keep up the great posts.
    You are definitely an entertaining poster.
    Please include more math and physics data to support your claims.

  36. #36
    just ride
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    you guys are thinking too much. my head hurts from this one.

    my bike steers as fast or as slow as I want it to. Its what my arms are for.

    that being said, my new 73hta Mamasita is coming next week so I will have something to compare to my 71 hta Gunnar. Maybe I will change my tune if I can feel a big difference. Maybe not.
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  37. #37
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    The steeper the HTA, the more rake you need.

    Wow, glad we sorted that one out.
    No longer member of the bike industry nor society, so don't hassle me.

  38. #38
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    Good job! Another thing

    Quote Originally Posted by Thylacine
    The steeper the HTA, the more rake you need.
    No, for spider 29" with 73' HTA you would need a non-existant Reba fork with 35,32, or even 30mm of offset instead of 38mm. That is what I conclude. It will increase the trail making it more stable and a little bit slower handling.
    Of course the front wheel will get too close and you are likely to get toe overlap, but for the sake of research I am right, am I? And then to resolve this one would have to make a bit longer top tube to compensate for shorter fork offset.

    Wow, glad we sorted that one out.
    Not completely, see Gary Fisher's Genessis II fork offset and shorter top tube ideas. Maybe something similar to G2 geometry will prevail in all 29er designs.
    Shorter top tube + little longer stem to compensate for that + longer fork offset + 1 degree or more slack HTA. Is it the way to go?
    Last edited by Davidcopperfield; 05-10-2007 at 04:05 AM.

  39. #39
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    Think you missed the subtleness of my post.

    Anyway, if Fisher was the geometry genius you'd like him to be, we'd all be on bikes with 26" top tubes and 70mm stems.
    No longer member of the bike industry nor society, so don't hassle me.

  40. #40
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    Quote Originally Posted by Thylacine
    Anyway, if Fisher was the geometry genius you'd like him to be, we'd all be on bikes with 26" top tubes and 70mm stems.
    I agree he screwed up first 29er with Genessis I geometry which included longer top tube and shorter stem and this while good for 26er is killing 29ers' handling and that is the point where all those opponets' sluggishness moaning comes from and that's why all sceptics think about 29ers as buses, tankers or coaches.
    The alleged G 2 is going to fix it, will it ? No idea. But coming to fork offset HTA and stem lenght something alike to G2 would be wise.

  41. #41
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    David Copperfield Doesn't Even Actually Own Any Bicycles.

  42. #42
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    Quote Originally Posted by VERVE 29er
    Whatta pack of A$$HOLES!!!!

    I think all the guy is asking is if the new 51mm offset fork will make bike like the Spider with a 73* HTA so twitchy that they will be unbearable on downhills and consequently make 29ers with 70.5* head angles handle similarly to 29ers with 72* and 38mm offset forks.

    Jeez, Tina
    Hey, *******tte, read all his other posts before you judge us.

  43. #43
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    Quote Originally Posted by GeoKrpan
    I wouldn't get a Spider. Read the MTBR full suspension 29er shootout.
    I would not trust all of those guys from that shootout. Most of them have never even ridden a 29er before. But I think I know what comments from that review you are talking about. It is attached below. Riders name is undisclosed because I do not want to embarrass him/her.


    <i>Then we hit steeper descents…this is where the Intense just got plain scary. I am no stranger to endo’s, and I’ve actually gotten pretty good at “landing” & avoiding them…but this bike feels like it’s literally waiting to launch you over the bars like a sprung trap!! It did get my heart going’ pretty good…along with some animated faces and language…OK, time to switch!</i>

    You have to take with a grain of salt a comment from someone who does not know how to or is scared to ride the real sections of the trails. Kind of funny to read really.

    Or you can look at the comments by those who own Spiders and other 73 degree bikes. Opinionated feel is a different animal that performance. On my Spider I am going down more on it than I was on my 69 degree 5” 26er.

  44. #44
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    and apparantly DavidCopperfield takes his bike knowledge from Mountain Bike Action.

    Woohoo.
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  45. #45
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    Hey now. DC asked a valid question and it helped clear up a mental road block that I had as did possibly IBIKEAZ. We both have recently joined the 29er club and maybe we were a little concerned that there might be a fundemental change in the way that 29ers resolve their steering attributes. I plan to have my bike for a long time so I just need to re-understand this aspect of bicycles again in my life.

    So what if DC doesn't have a bike. He wants one and (un)fortunately uses a forum to help him decide albiet in a frusturating and an "academic" way. Hopefully he gives up the need for an Intense and picks up a Haro Mary or a MC and learns the practical way.

    If you don't like his posts don't respond to them but I have gleaned a lot of information from these posts, less so from the original content but more so from the resulting discussion hence discussion thread.
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  46. #46
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    Ha

    One thing to consider about the 73 degree HA on the Spider (Reba set at 80mm). Once you factor in sag (rear) it is closer to 72. I have ridden the Spider and currently own a HT with a 72. Despite the differences with a HT and FS they steer similar. Also think about your bar length. The wider the bar the slower it will steer.

    IMO with the “current version” of the Reba (set at 100mm) mounted to a Spider with wide bars is a quick (not twitching) CC bike. Isn’t that want we want out of a CC bike?

  47. #47
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    Ted did a really good job of breaking this down into digestible chunks.

    Just wanted to add a piece that we learned at Fisher in developing the G2 bikes.

    As we increased the fork offset, reducing the trail, we needed to reduce the rider's reach to the handlebar, allowing the rider to more effectively weight the front wheel. That is the fundamental compromise with placing a new offset fork on an existing frame platform. If you don't adjust your position on the bike relative to the front wheel, you will change your ability to weight that wheel for traction which has a significant impact on steering. This is something the Keith Bontrager pounded home during our development.

    This does not mean that adding a new offset fork to your bike wont be just the right thing... But, it is very difficult to address how an individuals bike will handle with the new offset without knowing the rest of the rider's set-up (stem extension, traditional bar or Mary? etc). Discussing HT angle alone is only a fraction of the overall picture...

    Cheers

  48. #48
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    Oops, sorry for the incomlete post.
    The 29ers bikes tendancy to endo is related to one significant relationship. The riders center of mass relative to the position of the front axle.
    Headtube Angle and offset can move the front axle forward increasing the wheel base and decreasing the angle of center of mass to the front axle. Similarly, compared to the 26er the higher front axle on the 29er causes the 29er to be less prone to endo assuming the same rider position on the bike. (assumes the same BB height).

  49. #49

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    FWIW, total contact patch size is neither determined by HA, fork rake, or tire width/diameter. It is a function of air pressure in the tire. A 150 pound rider on a 30 pound bike with 30 psi in the tires will have a 6 square inch contact patch between the two tires. Depend on the weight distribution, the contact patch in back will likely be larger than the contact patch in front because more weight is typically over the rear tire.

    Inasmuch as altering the head angle, fork rake, etc, changes the fore/aft weight distribution, it is possible that such changes could alter the area of the contact patch in front, with a corresponding decrease in contact patch size in the rear.

  50. #50
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    Quote Originally Posted by shiggy
    These guys still understand bicycles better than you do

    That was great!

    For such a sorry first post, this thread has received quite a bit of attention, some of it actually informative--no thanks to the OP

  51. #51
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    New question here.

    Quote Originally Posted by garyfisherguy

    As we increased the fork offset, reducing the trail, we needed to reduce the rider's reach to the handlebar, allowing the rider to more effectively weight the front wheel. That is the fundamental compromise with placing a new offset fork on an existing frame platform.
    Develop it please, by placing 51mm fox offset you have shortened top tube and have put longer stem to keep the handle bar in the same position as in G 1 29er? In this the mystery?
    That is what I/we wanted to figure out from my 1 post onwards.

    If you don't adjust your position on the bike relative to the front wheel
    Let's say you have Sugar with G1 geometry and out of the blue you put fox with 51mm, what will happen with the steering ability for that unpredestined G1 frame?
    And one may adjust it by moving saddle bolts forward or backward?

    you will change your ability to weight that wheel for traction which has a significant impact on steering. This is something the Keith Bontrager pounded home during our development.
    So how handle frames not prepared for new offset? I can deduce that those with less or equal than 71,5' HTA will manouevre much better and those with more than 71,5 will become too twichy. This detail is very important for everyone, as we are on the verge of introducing new pattern which can be little compatible backwards.
    and
    This does not mean that adding a new offset fork to your bike wont be just the right thing...
    But, it is very difficult to address how an individuals bike will handle with the new offset without knowing the rest of the rider's set-up (stem extension, traditional bar or Mary? etc). Discussing HT angle alone is only a fraction of the overall picture...
    Let's take under loupe those first G1 29ers sluggishness' culprits, will they steer more nimble with new offset with exactly the same equipment? Remember they still have too long top tube.
    Has anyone tried this experiment?
    For sure this will affect wheelbase which will become too long, but more nimble the whole bike?

  52. #52
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    G1 Fishers ride fine. They just ride "bigger" than anyone has ever had before they came into existence. Big can be good, if you trails don't look like what I would build in a back yard if I had one.

    G2 fork in G1 bike with be about as quick handling (trail figure, you calculate the last digits behind the comma) as an On-One (72º HTA) with it's rigid fork (47mm). A longer front end yes. But only by a half inch over said On-One, so nothing much, and even rather hard to actually measure.

    I don't see the shorter top tube on the G2 as something they HAD to do, just something that is a nice opportunity. Try something new, and it helps make the Small frames actually fit as Smalls on a 29"er, without toe overlap or overly slow handling.

  53. #53
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    Does that mean you'll...

    Quote Originally Posted by garyfisherguy
    Ted did a really good job of breaking this down into digestible chunks.

    Just wanted to add a piece that we learned at Fisher in developing the G2 bikes.

    As we increased the fork offset, reducing the trail, we needed to reduce the rider's reach to the handlebar, allowing the rider to more effectively weight the front wheel. That is the fundamental compromise with placing a new offset fork on an existing frame platform. If you don't adjust your position on the bike relative to the front wheel, you will change your ability to weight that wheel for traction which has a significant impact on steering. This is something the Keith Bontrager pounded home during our development.

    This does not mean that adding a new offset fork to your bike wont be just the right thing... But, it is very difficult to address how an individuals bike will handle with the new offset without knowing the rest of the rider's set-up (stem extension, traditional bar or Mary? etc). Discussing HT angle alone is only a fraction of the overall picture...

    Cheers
    .,..be using shorter effective TTs? I sure hope so. Then I'll be able to consider a GF. For years I've always thought you folks put out a good bike for the buck but never considered them due to their wacked out geo (though I'm sure some folks like it). The short stem-long TT makes for an endo-proof rig but otherwise I personally find they handle poorly. Read this... relatively short TT, longer stem, relatively slacker HTA, more fork rake makes for a nice ride. With this set up you'll still get the endo-proofing via a the slack HTA, and all the benefits of a longer stem. Short stems make for choppy, slow speed steering. they are fine for open, high speed runs but otherwise, no good. A longer stem acts like a poor man's Hopey steering damper.

    Just my opinion of course.

  54. #54
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    The thing with G1 for me, the rider is really in control, but it required having an active mindset. Other geo's sometimes seem to do all the work by itself, but that makes (at least me) lose precision.

  55. #55
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    Caution;  Merge;  Workers Ahead!

    [QUOTE=GeoKrpan]
    I have the impression that putting a fork with the new offset on a first wave 29er with a HTA of 72 degrees or greater is NOT a good idea. I think it would make the front end too steep. Not good on steep technical downhill. It might be OK with a rigid fork but I think it would be a disaster with a suspension fork..
    First and foremost as was clarified new offset is just more space between steerer tube and stanchions. IT DOES NOT steepen the stanchions. Perhaps 72' HTA + 51mm offset on new fork crop will make the bike overly nimble and over steereable, however it might do the job with keeping the top tube shorter and with offset - providing enough clearance for fatter tyres.
    - For some XC racers it might do the job to get the bike quicker to maneouvre amongst trees and tight switchbacks. Such batch of bicycles would rather be unbearable for untutored person, but be excellent nimble and twichy XC race Only.
    - Steep 73'/72,5 HTA with 51mm offset is less prone endo than with 38mm offset on DH sections as it inscreases the wheelbase and moves our weight backwards in terms of front wheel. The virtual point is more on the back of the front wheel. Do you want me to draw it for you?
    These ought to bear a sticker For Racing Only

    Whereas for marathons you would need a bit slacker HTA instead of 73/72,5 72 or 71,5 + WB 43mm or Fox 51mm offset. And maybe a longer top tube and shorter stem? G I Geometry. Why? to keep beteer traction and grip. As far as marathons are concerned they have fewer tight bends than XC races. These bikes ought to bear a sticker "Marathons Only"

    For every day 29er biker something in between will be the golden point and the most practical.

    Quote Originally Posted by GeoKrpan
    The key thing here is keeping the fork trail the same.
    A "first wave" 29er will ride just like a "new wave" 29er if the fork trail is the same.
    The top tubes can be identical.
    If top tubes are the same and offset is changed the wheels base diffenrence ensues and thus handling characteristics. The one with shorter TT will be more practical for XC races and the second with longer TT and more offset better for marathons perhaps someting like
    Genessis I with more offset? but the wheel base might be too long.

    The "new wave" 29er will have a slacker HTA but a steeper fork
    The "first wave" 29er has a steeper HTA but a slacker fork.
    They will handle the same if the fork trail is the same. Trail is trail no matter how you arrive at it.
    Due to tiny (51-38=13mm or WB 44-38= 6mm) difference in th wheelbase. The shorter one will have smaller turning radius in comparison to the one will longer TT. It is like math compasse. The one with shorter TT will draw a smaller cirle with smaller radius and the latter, longer. The latter is likely to be less usable in tight switchbacks. G I is the latter and was the first to be released and not suitablr for XC races. People complain for its steereablity and nimblelessness and on steep acends (with too long TT) the front wheel is more to go up ine the air, shorter TT allows you to weight more front wheel.
    G I is the culprit for our suffering of sceptics' myths. If the Spider 29" had been released as the first 29er it would have enticed an still entice more bikers to switch for real 622mm MTB

    [...]
    The advantage of a "new wave" 29er is less chance of a toe overlap problem and that in the future the new offset will be the only one available.
    The advantage of a "first wave" 29er is that they are available NOW and there's no disadvantage unless you need a small frame size. The old fork offset should be around long enough for you to get your money's worth out of it.
    I wouldn't get a Spider. Read the MTBR full suspension 29er shootout.
    What do you think about such observations?
    Last edited by Davidcopperfield; 05-13-2007 at 03:00 PM.

  56. #56
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    Quote Originally Posted by donkey
    I'm honestly a little surprised that this guy hasn't been silenced/banned yet. Holy crap.

    He's like the new Cloxxi.
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  57. #57
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    Thanks Fran!

  58. #58
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    I just finished a new 29er frame - 70 degree head angle with a 55 fork offset. Yes, pictures coming soon.

    Why? There's two components to front end handling - trail (essentially high speed stability) and wheel flop (low speed maneuverability). The first generation 29ers used steeper head angles to match the trail of 26ers. But that decreased wheel flop. I had noticed that my past 29er frames with 72 head angles were really reluctant to go around switchbacks. But I never thought it had to just do with the bigger size. Adding a few inches to the effective length of the bike shouldn't do that. I wondered if getting back some of that missing wheel flop would help the front end change directions.

    So for this frame, I went with numbers that would give me about the same trail as usual, and give me just a little bit more wheel flop that a 26er. I figured that the bigger wheel was at least bigger, so maybe a little more wheel flop was justified.

    On this frame I also ran the stays pretty long - they're somewhere around 17.5", or whatever my 34 x 20 gear ended up.

    I did shorten the top tube by going up one stem size - from a 105 to 120 so 15mm shorter. However, the offset and head angle still push the front end out an inch farther. The total wheelbase on this bike is actually two inches longer than the last frame I built.

    So on paper, with a 70 degree head angle, 17.5" stays, and 2 inch longer wheelbase, most people would expect this thing to ride like a beach cruiser.

    "Most people" would be wrong. This thing corners like a 26er. Actually, it does switchbacks like a 26er, and everything else even better. I can't believe how well this bike corners.

    In some lumpy, off-camber terrain you can sometimes notice the extra wheel flop tugging at the handlebars. But it's not a problem. On the next frame I'll probably split the difference and take out a little wheel flop to see where it starts getting that 29er uber-stability feel again. I could trade off a little bit of switchback prowess for a little more lump and bump stability.

    Based on this experiment, I think G2 and other builders are on the right track.

  59. #59
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    Quote Originally Posted by dr.welby
    I just finished a new 29er frame - 70 degree head angle with a 55 fork offset. Yes, pictures coming soon.
    That sounds really cool. I'd like to build a bike like that, but I'd like to have a frame like that that can take both a rigid AND suspension fork without changing the geo very much. I guess I'm waiting for the susy fork makers to make better offsets...

  60. #60
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    Quote Originally Posted by dr.welby
    So on paper, with a 70 degree head angle, 17.5" stays, and 2 inch longer wheelbase, most people would expect this thing to ride like a beach cruiser.

    "Most people" would be wrong. This thing corners like a 26er. Actually, it does switchbacks like a 26er, and everything else even better. I can't believe how well this bike corners.
    Dude, you are not gonna slip this one by on us. 2" is ALOT. And yea, it might handle like a 26er, a long wheelbase shallow head angle one.

  61. #61
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    Here's a pic of the bike.
    Attached Images Attached Images

  62. #62
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    Good job!

    Quote Originally Posted by dr.welby
    I just finished a new 29er frame - 70 degree head angle with a 55 fork offset. Yes, pictures coming soon.
    Yet, wheelbase must be long. Perhaps you could use 71,5 HTA with WB 44mm or Fox 51mm. How would you jugde two options in terms of handling and what stem lenght would you recomend to get the most of those ratios? Steeper HTA and less offset will shorten the wheelbase, thus allow you to steer better in tihght switchbacks.
    I would suggest everyone paid attention to this as we are on the verge of settling the ideal HTA&Fork Offset& Stem lenght ratios then we can separate those several patterns into XC Trail AM FR DH spectrums.
    We are pretty different form 26" crowd because we have to or at least should carry out some research & development if we do not we shall not entice mainstreamers to make our ideas for us. It is like a mission for 29" humanbeings , whreas 26 mob has everyting and can be lazy since everything will be made.

  63. #63
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    What?

    I am a totally confused 29" humanbeing....

  64. #64
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    lolz!!
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  65. #65
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    Quote Originally Posted by Davidcopperfield
    Yet, wheelbase must be long. Perhaps you could use 71,5 HTA with WB 44mm or Fox 51mm. How would you jugde two options in terms of handling and what stem lenght would you recomend to get the most of those ratios? Steeper HTA and less offset will shorten the wheelbase, thus allow . . .snip . . .snip . . .
    Well, glad to see we finally <b>Got this sorted out! </b>

  66. #66
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    You guys are thinking waaaay too hard!

    Look, it's rather simple really. There are going to be several different head tube angles, offsets, and axle to crown numbers in use on 29"ers for years to come.

    Just look at your 26"er brethren out there. See what I mean?

    Different tuning options for different trail situations/ riding preferences. That's as it should be.

    This talk of "setting a 29"er standard" is rediculous.

    Take for instance the bike posted by Dr Welby. I wouldn't want a thing to do with that geometry, yet he likes it. Great, so who's right and who's wrong? What "standard" should be derived from this? Nobody and nothing.

    In a general sense there is going to be a divergence between AM/FR/DH type 29"ers and XC/Trail 29"ers, with one getting higher trail figures/ slacker head tube angles and the other getting more offset and sticking with the general 71-73 degree angles we have already.

    Of course, having different offset forks and different axle to crown measurements makes experimentation irresistable. I say, good!

    The best thing one can do is actually ride something on their home trails and judge for themselves. This post has entered the "mental masturbation" phase and has lost it's usefullness.

    I'm gonna go test my latest fork/frame match up on some dirt now. What are you gonna do?
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  67. #67
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    Quote Originally Posted by Guitar Ted
    Of course, having different offset forks and different axle to crown measurements makes experimentation irresistable. I say, good!

    The best thing one can do is actually ride something on their home trails and judge for themselves. This post has entered the "mental masturbation" phase and has lost it's usefullness.
    I know what you're saying. There's too much theorizing going on and not much reduction to practice.

    I built the above frame purely to test an idea I had:

    "Are 29ers harder to get around switchbacks because they have less wheel flop than 26" bikes?"

    I tested this, and in not a very subtle way. At some points in the design process I was worried I was going to burn up a tubeset on a piece of crap design (done it before...). However, in the end it worked out far better than expected. Out of the three 29er frames I've built, this is by far the best handling for me, in my terrain.

    And I think a lot of it is minutia. Yeah, the wheelbase is 2" longer than my last bike. Big whoop, that's 5%, and still smaller than the 10% change in wheel size from 26 to 29. Yeah, the stem is longer by one size. Big deal. It's the same as on my first 29er and shorter than the stems I had on all my 26ers going back to 1989!

    But on the other hand, this discussion is needed. Not many people understand trail and wheel flop and where it can work with you or against you. I wouldn't have designed for wheel flop if I hadn't been following the discussions on the net about French porteur bike design, and then made the connection to what Jeff Jones and Wes Williams are experimenting with.

  68. #68
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    dr.welby
    Thanks very much for your comment. I've been looking for an answer about this very question (whell flop for a constant trail) since 6 months now !

    I have 3 questions:
    - I suppose that your bikes "wanders" more when you climb of the saddle, leaning it from side to side, isn't it ? Is it a problem or not ?

    - Since i moved away from the mountains, i put on a longer stem to be able to weight the front more to get more front grip on the corners. By moving the front whell so much in front, you remove some weight on it. Do you still have the same front grip in a flat corner ?

    - Let's imagine one wants to keep the same front/center (same position of the front whell/BB), and the same position of the handlebar / saddle, and the same trail. So the exact same weight distribution. But wants more whell flop, and so use a slacker angle along with more rake. He will have to use a shorter top tube, and a longer stem. How would this affect the steering ?

    PS:
    I'm always surprised in this forum when someones speaks of "thinking too much". I can't understand how somebody can think too much ? Builiding a nice model by thinking is as important as collecting information by experiment, if you want to create a great design. But well, i'm a scientific researcher...
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  69. #69
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    Quote Originally Posted by 20.100 FR

    PS:
    I'm always surprised in this forum when someones speaks of "thinking too much". I can't understand how somebody can think too much ? Builiding a nice model by thinking is as important as collecting information by experiment, if you want to create a great design. But well, i'm a scientific researcher...
    We call it "analysis paralysis" here in the States. It's when people sit around theororizing all day and never take action, or at least show that they are, in fact, trying out the multitude of theories that they are propagating.

    Surely as a scientific resesarcher you understand that at some point action needs to be taken or all the thoughts in the world on a particular subject are like a worthless wind.

    This is what I'm referring to when I say, "you guys are thinking waaaay too much".
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  70. #70
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    Longer stems require larger movements to effect the same amount of steering input, so in otherwords, shorter stems generally equate to needing smaller movements to produce a change in steering/direction.

    Easy to visualise - imagine stem length is a radius. If you have a R120 vs an R100, to swing the radius 10 degrees, you'd have to move the R120 further than the R100.

    I dunno. Is that 'thinking too much"?
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  71. #71
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    I think Welby may have brought some weight back to the front by increasing chainstay length? When I added an inch to my Redline's CSL (2" of extra chainlinks, horizontal drops) that resulted in a very positive feeling front end.

  72. #72
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    Quote Originally Posted by Thylacine
    Longer stems require larger movements to effect the same amount of steering input, so in otherwords, shorter stems generally equate to needing smaller movements to produce a change in steering/direction.

    Easy to visualise - imagine stem length is a radius. If you have a R120 vs an R100, to swing the radius 10 degrees, you'd have to move the R120 further than the R100.

    I dunno. Is that 'thinking too much"?
    This is the classical point of view, but i have troubles relating it to my experience.

    I have a GT peace 9er wich is a slow handling bike. And yes i have to steer it by turning (forcing) the handlebar in tights corners. But for larger turns, and for every turn on my beloved Surly KM (or my road bike or my olds 26ers), i do not rotate the bar to turn : i lean the bike, and the front whell turns by itself, and the bar, and thus my hands, just follows...
    On my KM, switching to a longer stem gave me more front grip, without slowing it down... But it also changed my position and weight distribution

    I have the sensation that in my "virtual experiment", a longer stem would gives more stability to the front, with more leverage from the stem, the front wheel would be not so easily put off line by a rock/bump.

    It would be interesting to have some imput on some guy riding/designing BMW duolever motorcycle front suspensions system, where the stem length is not related to weight distribution (like on the Monolith prototype pictured as my avatar)
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  73. #73
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    What about a steering column in stead of a steerer with 2 "around the corner" joints, allowing a classical stem and top tube setup, but a hugely slack HTA plus offset. Same fit geometry, same trail, same wheelbase.
    Last edited by Cloxxki; 05-16-2007 at 05:21 AM.

  74. #74
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    Another thing to remember is the 38mm offset was decided upon back when forks had 2" of travel, and it was to take into account the change in head-angel, wheelbase and trail as the fork compressed. Rigid forks had more offset back then (like around 45mm) and its pretty silly they've kept a 38mm offset as fork lengths for XC alone have doubled in most cases.
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    Quote Originally Posted by 20.100 FR

    - I suppose that your bikes "wanders" more when you climb of the saddle, leaning it from side to side, isn't it ? Is it a problem or not ?
    It does have a different feel out of the saddle. But it's not a problem. Remember, I'm not using that much more wheel flop than a 26er.

    - Since i moved away from the mountains, i put on a longer stem to be able to weight the front more to get more front grip on the corners. By moving the front whell so much in front, you remove some weight on it. Do you still have the same front grip in a flat corner ?
    I still have good weight distribution, but I also made the chainstays longer. This has its own consequences. For me, climbing traction hasn't been affected. The bike is a little harder to manual but that's not too critical around here.

    I actually went with the longer stays for a funny reason - I wanted to run a Thompsen seatpost with no offset and Brooks saddle without having to pound it back all the way on the rails. To get my position where it needed to be, I needed a 71 degree seat angle. So to get tire clearance behind the seat tube without having to offset or bend the seat tube, I just made the stays longer. I figured since the front center was getting longer I could just make the back end longer and the weight distribution would not change.

    Quote Originally Posted by 20.100 FR

    - Let's imagine one wants to keep the same front/center (same position of the front wheel/BB), and the same position of the handlebar / saddle, and the same trail. So the exact same weight distribution. But wants more wheel flop, and so use a slacker angle along with more rake. He will have to use a shorter top tube, and a longer stem. How would this affect the steering ?
    As someone already said, a longer stem is usually thought to slow down steering, or at least the perception of steering, since for a given sideways displacement at the bar it sweeps out a smaller angle. I've also thought there might be a tiller effect when braking. Having a longer stem might be like having more trail. As you brake and resist your forward inertia with your hands on the bars you create a self-centering condition.

  76. #76
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    Quote Originally Posted by Cloxxki
    What about a steering column in stead of a steerer with 2 "around the corner" joints, allowing a classical stem and top tube setup, but a hugely slack HTA plus offset. Same fit geometry, same trail, same wheelbase.

    I need a drawing for this one...
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  77. #77
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    Quote Originally Posted by Thylacine
    Longer stems require larger movements to effect the same amount of steering input, so in otherwords, shorter stems generally equate to needing smaller movements to produce a change in steering/direction.
    Right, though you need more energy to change direction/turn with shorter stem.

    Easy to visualise - imagine stem length is a radius. If you have a R120 vs an R100, to swing the radius 10 degrees, you'd have to move the R120 further than the R100.
    The longer the stem, the more leverage effect you obtain, therefore more power is transfered into the wheel.
    It is science- when you have a heavy booulder/stone and you want to lift it, you need to put a falcrum (supporting point) really close to the given object and have a very long lever so that you use small energy input to move the object. The shorter the lever, the more energy you use to raise the object. I think stems work this way

    Quote Originally Posted by 20.100 FR
    - Let's imagine one wants to keep the same front/center (same position of the front whell/BB), and the same position of the handlebar / saddle, and the same trail. So the exact same weight distribution. But wants more whell flop, and so use a slacker angle along with more rake. He will have to use a shorter top tube, and a longer stem. How would this affect the steering ?
    Well you would be very close to Genessis II however they seem to use the same HTA, but in comparison to Gennesis I they have shortened the Top tube, lenghtened the stem and increased the fork offset, yet the point in which you rest your hands upon stays in this same place. You are not crumped more or in elongated position, yet you get nimble G II bike, whereas G I is sluggish. Of course this concept might be implemented into any 29er you imagine, I surmasize.
    My perception of ideal nimble and all-around 29 geometry
    Some draft outlines, do not take the given ratios for granted it is just my poor drawing skills

    Genessis I

    Sluggish bike, but perhaps better for maratons, how do you think?

    Like Genessis II

    Point 1 shows us where the weight is placed and 2 shows us how the weight is thrusting the wheel forward and making it less pinned to the ground and thus lighter to maneouvre. But is it the grip that we trade off for nimble steering? Does less trail mean less grip?
    Best 29er front end geometry.
    Within this geometry we may differentiate several HTA angles, which will change the wheelbase and destine for XC Trail AM FR or DH bike.

    Please take your time to read all my posts in this thread and comment them, if I am somewhere mistaken, let me know. I am going to work for one bike manufacturer and must know if I am on a good path.
    Last edited by Davidcopperfield; 05-16-2007 at 03:56 PM.

  78. #78
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    Taking a look at "The Way Back Machine"

    Quote Originally Posted by dr.welby
    As someone already said, a longer stem is usually thought to slow down steering, or at least the perception of steering, since for a given sideways displacement at the bar it sweeps out a smaller angle. I've also thought there might be a tiller effect when braking. Having a longer stem might be like having more trail. As you brake and resist your forward inertia with your hands on the bars you create a self-centering condition.
    I come from the era when a "short" stem was anything less than 135mm. In fact alot of us ran up to 150mm stems on our XC machines.

    The idea was that a longer stem helped with climbing. It allowed one to get weight out over the front wheel to keep it down and also from doing the dreaded wheel flop. (You definitely didn't want wheel flop on a steep climb) The longer stem kept leverage over the front wheel getting knocked off line enough to cause wheel flop.

    As Thylacine astutely pointed out, a longer stem causes you to swing a wider arc to complete a turn than a smaller stem would. That's one of the reasons you almost never saw XC handlebars longer than 23" back then, and then most racers were cutting them even shorter. Shorter handlebars meant less radius for the hands to travel in tight turns.

    In no way are you gaining any kind of an advantage during braking with a certain length stem other than from a standpoint of weight distribution concerning the rider, and that assuming the rider doesn't move at all from a seated posistion.

    Again, this is slicing hairs. It disregards the other aspects of the frame design and geometry which must be included, as Dr Welby is trying to do as he describes his personal rig. Which I might add, is working for him, it would seem. Our mileage may vary. His set up is custom, which paints his results in a very small corner as to this discussion. I would imagine a custom set up for any one of us might vary quite a bit from his, don't you?

    As a for instance, I am having a 19" Badger frame made that mimics the Dorothy geometry that I rode last fall. 72 degree head angle, 38mm offset and along with the White brothers fork, and other geometry aspects, was the most intuitive handling bike I have ever ridden, period. No wheel flop. Steering from the hip. descended with confidence, and cut corners as if on rails. By the way, it had a 100mm stem, if you care to know. I think this is about as far removed from Dr Welby's bike as you can get, yet it's my ideal.

    Again, nobody is right or wrong, but it's nice to know you can experiment with these new offsets and head angles to dial in your ride exactly in the way you imagine it should be. Of course, this requires alot of personal work and research. Lot's of money and time spent. It's not everyone's cup of tea to do this, and not everybody can afford to, but this along with a custom bike fitting is really the only way you are going to figure this stuff out for you. No easy way out.
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  79. #79
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    Why G2 came about

    Well you would be very close to Genessis II however they seem to use the same HTA, but in comparison to Gennesis I they have shortened the Top tube, lenghtened the stem and increased the fork offset, yet the point in which you rest your hands upon stays in this same place. You are not crumped more or in elongated position, yet you get nimble G II bike, whereas G I is sluggish. Of course this concept might be implmented into any 29er I surmasize.
    Just to clarify a point, Fisher was getting concerns about G1's sluggish slow speed handling. This is what G2 was primarily designed to address while trying to keep all the other positive attributes of the previous Genesis geometry.
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  80. #80
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    Quote Originally Posted by Guitar Ted
    Again, this is slicing hairs. It disregards the other aspects of the frame design and geometry which must be included, as Dr Welby is trying to do as he describes his personal rig. Which I might add, is working for him, it would seem. Our mileage may vary. His set up is custom, which paints his results in a very small corner as to this discussion. I would imagine a custom set up for any one of us might vary quite a bit from his, don't you?

    As a for instance, I am having a 19" Badger frame made that mimics the Dorothy geometry that I rode last fall. 72 degree head angle, 38mm offset and along with the White brothers fork, and other geometry aspects, was the most intuitive handling bike I have ever ridden, period. No wheel flop. Steering from the hip. descended with confidence, and cut corners as if on rails. By the way, it had a 100mm stem, if you care to know. I think this is about as far removed from Dr Welby's bike as you can get, yet it's my ideal.
    It's funny you mention that. The last frame I built before this one was 72 HA, Reba, and 100mm stem. And I really liked the fit and feel of that frame. This new one fits the same, but corners better for me. So while it's "about as far removed" on paper from what you like, you might be surprised if you rode it. Or maybe not. Only one way to find out, huh?

  81. #81
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    Wheel "tuck"....

    Quote Originally Posted by Guitar Ted
    I come from the era when a "short" stem was anything less than 135mm. In fact alot of us ran up to 150mm stems on our XC machines.

    The idea was that a longer stem helped with climbing. It allowed one to get weight out over the front wheel to keep it down and also from doing the dreaded wheel flop. (You definitely didn't want wheel flop on a steep climb) The longer stem kept leverage over the front wheel getting knocked off line enough to cause wheel flop.

    As Thylacine astutely pointed out, a longer stem causes you to swing a wider arc to complete a turn than a smaller stem would. That's one of the reasons you almost never saw XC handlebars longer than 23" back then, and then most racers were cutting them even shorter. Shorter handlebars meant less radius for the hands to travel in tight turns.

    In no way are you gaining any kind of an advantage during braking with a certain length stem other than from a standpoint of weight distribution concerning the rider, and that assuming the rider doesn't move at all from a seated posistion.

    Again, this is slicing hairs. It disregards the other aspects of the frame design and geometry which must be included, as Dr Welby is trying to do as he describes his personal rig. Which I might add, is working for him, it would seem. Our mileage may vary. His set up is custom, which paints his results in a very small corner as to this discussion. I would imagine a custom set up for any one of us might vary quite a bit from his, don't you?

    As a for instance, I am having a 19" Badger frame made that mimics the Dorothy geometry that I rode last fall. 72 degree head angle, 38mm offset and along with the White brothers fork, and other geometry aspects, was the most intuitive handling bike I have ever ridden, period. No wheel flop. Steering from the hip. descended with confidence, and cut corners as if on rails. By the way, it had a 100mm stem, if you care to know. I think this is about as far removed from Dr Welby's bike as you can get, yet it's my ideal.

    Again, nobody is right or wrong, but it's nice to know you can experiment with these new offsets and head angles to dial in your ride exactly in the way you imagine it should be. Of course, this requires alot of personal work and research. Lot's of money and time spent. It's not everyone's cup of tea to do this, and not everybody can afford to, but this along with a custom bike fitting is really the only way you are going to figure this stuff out for you. No easy way out.
    With that little rake and a such a steep HA do you feel like your front wheel is a bit close on the steep descents? Of course the short stem serves as endo proofing. For a guy who started out "back in the day" with those long stems I don't see how you can get use to the shorter stem. I still can't get use to anything less than a 110mm. Anything shorter than that and it makes the steering feel too "quick and choppy" when worming through the slow terrain. Do you find your setup working well for any particular type of trails or would you say it's a no compromise setup?

  82. #82
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    Consider the differences

    Quote Originally Posted by Miker J
    With that little rake and a such a steep HA do you feel like your front wheel is a bit close on the steep descents? Of course the short stem serves as endo proofing. For a guy who started out "back in the day" with those long stems I don't see how you can get use to the shorter stem. I still can't get use to anything less than a 110mm. Anything shorter than that and it makes the steering feel too "quick and choppy" when worming through the slow terrain. Do you find your setup working well for any particular type of trails or would you say it's a no compromise setup?
    It might make more sense when you consider the differences. (I'll clue you in now though, the old days were severely endo prone!)

    Old bikes: 23" top tube- effective length. 26 inch wheels, saddle to bar drop of at least three inches, sometimes more. 135-140mm stems at zero to plus ten rise. Narrow, straight handle bars.

    New bike: 24.25" top tube- effective length. 29 inch wheels, saddle to bar drop of one to two inches. 90-100mm stems at ten to ( for drop bars) 40 degree rise. Wide, funky, swept back bars.

    What's the biggest difference? The wheels. Period. They radically changed the way I rode and looked at my set ups. I could get away with some things I never would have done on my 26"ers.

    Also, keeping in mind that I don't really steer the bike with the bars as much as I do with my hips. The bike was quick, so little physical effort was needed to initiate a turn or to keep it on line. (I'm speaking primarily of the Dorothy again) Downhills were relaxed, no sketchy characteristics. I never felt I was going to endo. Most of that is due to the wheel format, and a little to the extra length in the top tube. Think of it as going to more stable wheels and a dash of Genesis geometry thrown in there. (Although Rob might cringe at that comparison) My Surly is like this to a degree too. (I have an 80mm stem with 40 degree rise and dirt drops on that one) I don't seem to have any issues yet with these set ups anywhere I've ridden them.

    Conversely, I have ridden some 29"ers that I had to physically muscle around singletrack corners. Most notably the F-29 Cannondale and the stock set up on the Raleigh XXIX+G. Funny thing is,they both had similar trail figures. Hmm.......

    Hope that helps make sense of my post for you.
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  83. #83
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    hey Guitar Ted, can you please explain what you mean by "steering from the hip", and how you do it in practise. Ta.

  84. #84
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    Quote Originally Posted by Keholio
    No Jan here,
    Likewise I can be found in those long dark winter months perfecting my donut eating skills. My wife says she can hardly tell . . .
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  85. #85
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    I love you all, but PLEASE stop feeding the...
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  86. #86
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    For your cannondale and raleight test, how did you checked the trail ?

    I think that we can't really trust the official numbers. For trail, 10mm can be felt, wich is a vey little change on the front angle, and so we need acurate measurements on the real bikes.
    May be the only good way would be to use so kind of frame jig to check that ?


    In France, there is a very interesting little builder of steel road bike ( ! ), FKC, that only makes 650c bikes with NO rake (and more trail than the classical values). People and mags are raving about how it handles...
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  87. #87
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    Davidcopperfield,
    Your need to check back the definition of torque, speed, power and energy. Assuming that power only depends on torque is false. On your boulder example, you use the same energy whatever fulcrum you use...

    Trail has nothing to do with grip. Load distribution has.
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  88. #88
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    Quote Originally Posted by Davidcopperfield
    Right, though you need more energy to change direction/turn with shorter stem.

    The longer the stem, the more leverage effect you obtain, therefore more power is transfered into the wheel.
    It is science- when you have a heavy booulder/stone and you want to lift it, you need to put a falcrum (supporting point) really close to the given object and have a very long lever so that you use small energy input to move the object. The shorter the lever, the more energy you use to raise the object. I think stems work this way
    Energy expended = work done, work = force x distance. In the end it doesn't matter how long the lever is, it takes the same amount of energy (which happens to equal the weight of the boulder times the height it is raised in an ideal situation) to raise the boulder 1 inch wheather you are using a 1 foot lever or a 100 foot lever. You'll have to push the 100 foot lever over a longer distance, so the force is decreased, but the distance is increased.

    As it relates to stems: it is true that for a longer lever, less force is required. However, the lenght of the lever is dependent on the perpendicular distance from the direction the force is applied to the center of rotation. What this means is that the lever distance of the push pull force on the bars (running fore/aft parallel to the stem) depends only on the width of the bar. Stem length does not affect this lever distance at all. A longer stem effects lever distance for forces applied along the length of the bar only. Personally, I don't apply sideways force on the bars when I turn, only fore/aft. Even if I did, the typical person has comparatively little ability to apply force laterally vs fore/aft. Longer stems have a miniscule effect on the amount of force required to turn the bars.
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  89. #89
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    Is a troll anyone whose first language isn't English?

    My comments regarding stem length weren't related to force, just simply the distance you have to move your arms to generate the same directional change.

    Stem and bars are the unspoken part of the steering equation. They're almost never mentioned, but in my mind are equally as important as rake/trail/HTA.
    No longer member of the bike industry nor society, so don't hassle me.

  90. #90
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    why the heck is Firefox double posting on me? Maybe I need a restart?
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  91. #91
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    Try this

    Quote Originally Posted by PuddleDuck
    hey Guitar Ted, can you please explain what you mean by "steering from the hip", and how you do it in practise. Ta.
    Take your bike out and coast in a straight line. Then press inwards on the nose of the saddle with the upper part of your right leg and see what happens.

    Not every bike will turn well this way, but you'll see what I mean.
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  92. #92
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    Quote Originally Posted by Thylacine
    Is a troll anyone whose first language isn't English?

    My comments regarding stem length weren't related to force, just simply the distance you have to move your arms to generate the same directional change.

    Stem and bars are the unspoken part of the steering equation. They're almost never mentioned, but in my mind are equally as important as rake/trail/HTA.
    As is tyre profile, which effects the quickness of turning via leaning. The number of things that influence bike handling are huge, but it is a lot easier to say that trail is the important number.
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    Hey come on man! Don't diss DavidCopperfield. I read every one of his post and find them (if not informative) very entertaining. If you don't "get it" try drinking 12-16 oz of cough syrup and read it again. Then you will see the "magic" in what he posts.

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    Quote Originally Posted by Secret Squirrel
    Hey come on man! Don't diss DavidCopperfield. I read every one of his post and find them (if not informative) very entertaining. If you don't "get it" try drinking 12-16 oz of cough syrup and read it again. Then you will see the "magic" in what he posts.
    Personally, slamming my left hand in my desk drawer 8--10 times then reading his posts seems to work for me . . . .

  95. #95
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    Quote Originally Posted by Random Drivel
    Personally, slamming my left hand in my desk drawer 8--10 times then reading his posts seems to work for me . . . .
    True, but if you want to read this entire thread try sticking your head in that drawer.
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  96. #96
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    Quote Originally Posted by Guitar Ted
    Take your bike out and coast in a straight line. Then press inwards on the nose of the saddle with the upper part of your right leg and see what happens.

    Not every bike will turn well this way, but you'll see what I mean.


    dh style

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    Quote Originally Posted by bcd

    dh style

    Thanks GuitarTed and BCD...I missed your response GT...I'll check it out. Ta

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    In this thread http://forums.mtbr.com/showthread.php?t=339319
    it is claimed that there is going to be no 51mm offset forks for aftermarket and my question is why?
    In my humble opinion there ought to be several offsets classical 38mm for frames with steep HTA 73,73,5' and a standart between 43-48 perhaps 46mm for newer 29" frames with a bit slacker HTA 71,5' and 51mm "G2" forks for slack HTA about 69' 29" frames. Or perhaps would you propose solely two standarts 46mm and 51mm because 38mm offset causes troubles - overlap in small 29" frames. What are your views?

  99. #99

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    Quote Originally Posted by Davidcopperfield
    it is claimed that there is going to be no 51mm offset forks for aftermarket and my question is why?
    Because Fisher has an '08 exclusive on them for their G2 geo bikes.

    Quote Originally Posted by Davidcopperfield
    What are your views?
    My view? This thread was a trainwreck 5 months ago. 5 months later nothing has changed. Let it die.

  100. #100
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    After reading many offset&hta orientedd threads I am wondering what is the ideal angle at which the fork compresses in the best way?
    For instance Spider 29" with 73 HTA and Reba 38mm offset will react and handle differenty than Hi-Fi 29" 69 HTA plus 51mm even when the trails of those bicycles can be this same or similar. We can keep the wheel base this same however the angle of the fork hhitng an obsctacle is different - how does this aspect affect handling?

  101. #101
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    more horizontal suspension (sliders) is better for shock absorption, but dives more while braking, and reduce trail faster under compression.
    Frenchspeaking 29"ers community site http://VingtNeuf.org

  102. #102
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    New question here.

    Hey relying on this report
    http://twentynineinches.com/2007/11/...ut-of-the-box/

    The measurements all agreed with the spec sheet with the exception that the static measurements of the head tube and seat tube came ot to 71/73.5 degrees respectively. A bit steeper than what Fisher has published

    What does it mean? How much trail shall we get combining 71 Ht with 51mm offset fork, the A-C lenght of which, we are not aware of? On fisher site there is 71,9mm of trail. Is there a mistake somewhere there or am I missing something?

    Okay I answered myself
    71 HTA + 51mm offset with 29"=736,6mm the trail is 73mm, and with 5.5 29er we get 71 HTA + 44mm WB offset = 80mm rather slow handling, but stable at speed.
    Last edited by Davidcopperfield; 11-24-2007 at 10:15 AM.

  103. #103
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    Is there a calculator, which counts the trail using also A-C lenght of a given fork and HTA + other variables?

  104. #104
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    Quote Originally Posted by Davidcopperfield
    Is there a calculator, which counts the trail using also A-C lenght of a given fork and HTA + other variables?
    BikeCAD by Bicycle Forest.

    You do realize that with knowledge of this tool, we are expecting from you many wonderful and innovative new long travel 29er designs!

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  105. #105
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    Quote Originally Posted by Davidcopperfield
    Is there a calculator, which counts the trail using also A-C lenght of a given fork and HTA + other variables?
    Good idea DC, why don't you prepare a simple model in MS Excel for all of us to use?

    Thanks.

  106. #106
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    Now following Genessis 2 from Gf we know that a 29er XC race bike ought to have 70-75mm of trail, short TT, conventional 71 HTA, about 51mm offset.

    What is the sweet spot standard for 29er AM bikes?
    How much trail does BCD have on his 29er dh bicycle(s)? For comparison how much does dh 26ers have?

  107. #107
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    Quote Originally Posted by Davidcopperfield
    Now following Genessis 2 from Gf we know that a 29er XC race bike ought to have 70-75mm of trail, short TT, conventional 71 HTA, about 51mm offset.

    What is the sweet spot standard for 29er AM bikes?
    How much trail does BCD have on his 29er dh bicycle(s)? For comparison how much does dh 26ers have?

    i have figed that b/f and am looking for the thread.................

  108. #108
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    here:

    here are some trail numbers. any slack dh bike is going to have long trail, its what we want too let loose.
    26x2.5 is 27'' tall
    boxxer fork rake is 42mm, 888 is 43.5, fox 40 is 44 so i averaged.
    my 29 fork offest would have to be 2.125 to have the same trail numbers as 43x27''

    HA---43mm 27''------43mm 29er-----my WB is 31mm!! 29er.

    63---5-----------------5.5--------------6
    64---4.7---------------5.2--------------5.7
    65---4.4---------------4.9--------------5.4
    66---4.1---------------4.6--------------5.1
    67---3.9---------------4.3--------------4.8

  109. #109
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    I know this has been beat to death, but I am considering a G2 Fox from my 08 Rig on a Niner MCR. The MCR has a HA of 72 around an 80mm fork with 38mm of offset. If you use a G2 51 mm offset fork and extend the travel to 100mm, how close to the original feel would the niner have?

    Head Angle Change:
    20mm increase in ATC reduces HA on Niner MCR from 72 to 71
    Fisher G2 Geo at 80 mm ATC has a HA of c70
    Niner states that their frame works well with either 80 or 100mm fork.

    Trail Change:
    Niner MCR w/80mm G2 51mm offset = 67 mm
    Niner MCR w/100 mm G2 51 mm offset = 74mm
    Niner MCR w/ 80 mm 38mm offset = 80 mm
    Niner MCR w/ 100 mm Fox 45mm offset = 80 mm
    Fisher Rig w 80 mm 51mm offset = 81.3mm
    Niner MCR w/100 mm 38mm offset = 87 mm
    Fisher Rig w/100 mm 51 mm offset = 88 mm

    Wheelbase change:
    51mm offset increases existing wheelbase by (51-38)= 13mm
    20mm increase in ATC increases wheelbase by (70/90 * 20mm)= 15.5 mm increase
    Total Wheelbase increase = 28.5mm or just over an inch.

    Logical Questions: If according to Niner, increasing fork travel to 100mm has relativeley no effect on handling despite a 7mm increase in Trail, would a 6mm reduction in trail combined with a longer wheelbase have much of a negative effect?

    If the Fox non G2 fork has the same trail at 100mm on a Niner MCR as the 38mm Reba at 80mm, would the Fox 45 mm fork be the ideal for running 100mm on this fork.

    If the above is true, to maintain the original intended balance in handling, a bike must increase offset by about 7mm for every 20mm increase in travel as this is the rate that trail increases.

    At what point during the changes in trail would an average rider actually notice?

    At what point in a reduction in trail would a bike become twitchey, nervous, or just not stable enough to navigate rought terrain? Maybe we should not be looking at the ideal trail, but the acceptable ranges of trail.

  110. #110
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    Quote Originally Posted by bcd
    HA---43mm 27''------43mm 29er-----my WB is 31mm!! 29er.
    67---3.9---------------4.3--------------4.8
    4,8" =121,92mm far too much you need something max 100mm trail
    The offset you need 2,125 " =53,975mm together with 67 HTA might become a standard for dh 29ers.
    Solution: Contact Ninerbikes and convince them to start producing DH 29ers and at this same time ordering a batch of Grooves 180/203 adjustable and/or 180mm with 54mm offset and you could order some units as well.
    A steeper HTA simplying, as it had been stated at the top of the page, may force the fork stanchions to exert too much pressure on the outer tubes and the whole damper to be tucked under down tube.

    El_Scottamonmtes
    I know this has been beat to death
    It has never beenn beaten to death, the more questions about this issue the more the geo can be tweaked.

    Trail Change:
    Niner MCR w/80mm G2 51mm offset = 67 mm
    Niner MCR w/100 mm G2 51 mm offset = 74mm
    Niner MCR w/ 80 mm 38mm offset = 80 mm
    Niner MCR w/ 100 mm Fox 45mm offset = 80 mm
    Fisher Rig w 80 mm 51mm offset = 81.3mm
    Niner MCR w/100 mm 38mm offset = 87 mm
    Fisher Rig w/100 mm 51 mm offset = 88 mm
    Anything over 80mm may render the 29er sluggish, see the G 1 trail naumbers it was 71 HTA + 38mm Reba = about 87mm + long TT and we get a cow. G 2 fixed this one with shorter TT and longer offset reducing the trail.
    An example of long trail and slack angle is Lenz sport f. ex. Behemoth and Lunchbox they are considered to be maneouvrable enough see twentynineinches.com for more in-depth analysis. Remember they are AM bikes.

    Wheelbase change:
    51mm offset increases existing wheelbase by (51-38)= 13mm
    20mm increase in ATC increases wheelbase by (70/90 * 20mm)= 15.5 mm increase
    Total Wheelbase increase = 28.5mm or just over an inch.
    Disadvantage: Remember that longer wheelbase means longer radius of turning in virages. How long will your wheelbase will be then?

    At what point during the changes in trail would an average rider actually notice?
    In trail I do not know yet in offset you can feel the change maybe from 2 or 3mm if you are skilled mtbbiker.

    At what point in a reduction in trail would a bike become twitchey, nervous, or just not stable enough to navigate rought terrain? Maybe we should not be looking at the ideal trail, but the acceptable ranges of trail.
    For XC and long travel 29ers 70-75mm but remeber the short trail tells you that you need little power to change track and you can be thrown out of rhytm by an obstacle as well. If you have long arms they provide additional long leverage which enables to turn the handle bar.
    Long story short a 200cm will feel different on G2 than 170cm or do I miss something?

    I do know more andswers to your questions let's wait for someone well-versed.

  111. #111
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    Quote Originally Posted by Davidcopperfield
    4,8" =121,92mm far too much you need something max 100mm trail
    The offset you need 2,125 " =53,975mm together with 67 HTA might become a standard for dh 29ers.
    Solution: Contact Ninerbikes and convince them to start producing DH 29ers and at this same time ordering a batch of Grooves 180/203 adjustable and/or 180mm with 54mm offset and you could order some units as well.
    A steeper HTA simplying, as it had been stated at the top of the page, may force the fork stanchions to exert too much pressure on the outer tubes and the whole damper to be tucked under down tube.
    .

    most dh bikes run the fox @ about 43.. offset, with a 27'' wheel and 64 head angle sitting on the bike. thatis 4.7 trail

    THAT is the NORMAL. 4.7 for race dh bike

    so for me to be in THAT ballpark is run the same fork and around a 66 head angle.

  112. #112
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    I was wondering:
    1.
    How much steering can be quickened just by fiddling with stems (risers or upside-down) and handlebars. Let's say how much can you improve the manoeuvrability of old fashioned 29ers with Reba 38mm offset

    2.
    The other theme I would like to toss around is the aspect of small 29er frames like 16" especially longer travel FS. For instance Small Rip9 and small Behemoth.
    All small frames should have even more offset because narrower shouldres of shorter riders do not produce enough leverage on the handlebars to steer as quickly as broader shoulders of taller riders.

    What do you think?

  113. #113
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    Has anyone fiddle with shorter stem rather than longer offset fork? Stem lenght vs offset= your views?

  114. #114
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    Quote Originally Posted by Davidcopperfield
    Has anyone fiddle with shorter stem rather than longer offset fork? Stem lenght vs offset= your views?
    wouldn't effect the handling of your bike except that it would be a shorter stem effectively changing your weight balance on the bike. Benefits is that it allows you to get over the back tire better. Negatives is that you sit upright more so you have less aero advantage on long rides and you have to shift your weight more over the front wheel when turning to gain bite lost in the shorter stem.

    It how ever does not change the trail factor that the offset effects which is the different between stability and twitchiness.
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  115. #115
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    I am pretty sure this next comment is going to get flamed ... but here goes:

    I put a G2 51mm offset on my RX29r because I trust Fox forks and I liked the way the black fork looked with the black Titus swingarm/rear triangle. After reading all this, I hope I am able to steer the bike at all!

    BTW, in case anyone is considering a similar build, there is enough clearance on a size L RX29 size large with a G2 so that the fork adjustment knob clears the frame when the front wheel is fully rotated. There is about 4mm of clearance. A little close, but no need to go to a +5mm wider lower headset cup.
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  116. #116
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    Interesting thread.
    roccowt.
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  117. #117
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    How about negative trail? Lets say change the for k offset to 400mm.

  118. #118
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    What is the offset for 36ers? What trail do they need? Do they feel slow handling?

  119. #119
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    Quote Originally Posted by Guitar Ted
    Although the Marz forks on early Fishers were 43mm, if I'm not mistaken.
    Not mistaken. The 2002 Mt. Tam 29er I retired recently came with a 43mm MXR (and a 71° HTA).

  120. #120
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    Old but not dead. With the new crop of longer travel 29ers- we get slacker angles like 69 and fork offset still residuates in 44-46mm spectrum. So http://www.kogswell.com/geo.php
    Introduce 737mm wheel which is 29" 69 hta and 44 offset Trail whooping 94mm -wow that is commn for FR/DH 26ers! now with 46 offset trail is 92mm still too much by 10mm for a trail bike or light AM.
    Now 69 hta 57 offset and we get 80mm of trail. Now we are talking. Most people want to have a light, fast turning responsive bike. All high trail bikes are rather sluggish or too stable- whatever you want to call- expect (pursuant to GT) Lenz Behemoth and Lunchbox.

  121. #121
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    Quote Originally Posted by mward
    Your credibility is suffering.
    As far as I know, there never was any

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  123. #123
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    Guys like you

    Quote Originally Posted by Law
    When I read this I just shook my head. You really don't know what you are talking about. I for sure don't know what you are talking about. "Contact Patch" does not change depending upon the head angle and offset as far as I can figure.

    You might be better off putting you thoughts into something more productive, like looking for porn on the web or something.
    Are the reason I enjoy riding with my dog. Also, you really need to get punched in the face. Just saying.

    Jaybo

  124. #124
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    What about 51mm G2 forks? Specialized uses one on their smallest women 29ers. Why isn't anybody else?
    Last edited by Davidcopperfield; 07-30-2011 at 11:59 AM.

  125. #125
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    Holy dead thread resurection Batman!

    You know what, you might be the last person on the interweb who really gives a flying **** about this sort of stuff.

    Glad you still care enough to post...

    SSP
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  126. #126
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    Well, I disagree it is very important to get the 29ers steer well. If they tend to be sluggish they won't get around a switchback or S-shaped trails which means they won't be sold etc.

    Long offset makes sens on XS and S frames where the feet come very close to the wheel. Instead of mking the TT too long or slackening the HTA too much it is much easier to do it with mire offset.
    All S frames ought to have 51-55 depending on the bike type choice.

  127. #127
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    Wow, being lectured on bike geometry by DC...short memories guys!

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  128. #128
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    I know, right?

    Quote Originally Posted by Singlespeedpunk View Post
    Wow, being lectured on bike geometry by DC...short memories guys!

    SSP
    Me: Titus RacerX29er

    I rode it for a while with a 38mm offset 1st gen Reba. Handled great... no toe overlap.

    Now a 45mm offset Lefty. I think I might actually like the 38mm offset more, but 45m is fine. I can make the super tight switchbacks the same either way, it's just that 'turn-in' feeling is taking a bit more to get used to.

    The last reason in the world for more offset should be to gain toe overlap clearance. I mean, what... 6mm is not a lot to gain to whack out the handling of your bike. There are plenty of good handling xs frames out there with no toe overlap even at 38mm offset.

    Heh... once nice thing about the Lefty with removable clamps... you can actually adjust your axle to crown about 2cm up or down if you like. I'm actually running mine as slammed down as I can in the clamps. I have it set for 110mm of travel, but I'm going to do a real test for clearance (ratchet strap the bars down to the bed of a truck) and see how much of the bottom out bump stop I can remove. I know a guy running it down to 125mm and still has a few mm of tire clearance with a 2.2" tire. I'm just playing safe for now.

    <a href="https://picasaweb.google.com/lh/photo/zgUTu7NKE9PtKbZv9uXuOQ?feat=embedwebsite"><img src="https://lh6.googleusercontent.com/-xDmzfHKP7fo/TioESy28RZI/AAAAAAAAVuU/Onm0TRF5xO8/s800/IMG_1086.JPG" height="800" width="600" /></a>

    Now, off for a dawn patrol BCOD early ride with a bud.

  129. #129
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    I swap between 26" wheels and 29" wheels frequently Reba SL 29 38mm offset, 29" to 26" I don't notice the change but if I've been riding 26" for a while and put the 29" on it does feel slower to steer, for about 5 seconds and then I adapt and it's all fine.

    68degree HA with 29" fitted so super slack in 29er world, 69.5degree with 26" fitted, the slacker angle will make the bike feel slower anyway.

    Yet again, there is really not much in it from 26" to 29" on the front for me, I just prefer the bars higher with the 29" fitted and slacker angle, 26" pushes the weight forward and makes for a better mud riding tool.

    Rear you'd get better use out of the rolling resistance and getting up things I'm sure, not enough to make me buy a 29er frame and rear wheel as yet.

  130. #130
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    Cube AMS SLT Full Suspension 29″er: On Test | Twenty Nine Inches
    Looks like the patent for 51mm forks for trek has expired. Will it be copied on other bike-fork set-ups?

  131. #131
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    Quote Originally Posted by Davidcopperfield View Post
    Looks like the patent for 51mm forks for trek has expired. Will it be copied on other bike-fork set-ups?
    What patent is that?

  132. #132
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    I don't think it was a patent, it was that Fox gave Trek OEM exclusivity on the 51mm forks for a certain time period since Trek probably paid for the tooling.

  133. #133
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    Is it now available on after market? Not really I guess. How come Cube uses it and Specialized offers it on women specific 29ers?
    51mm is a part of G2 geometry. So now any bike can have G2?

  134. #134
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    Quote Originally Posted by Davidcopperfield View Post
    51mm is a part of G2 geometry. So now any bike can have G2?
    That's a stupid question. Any bike can have 51mm offset and always could. "G2 geometry" is a marketing name possibly covered by trademark. Forks are limited by what is made and what the distribution arrangements are. Trek doesn't own any right to 51mm offset and never did.

  135. #135
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    Quote Originally Posted by Davidcopperfield View Post
    So why no other fork came with 51mm offset? Why didn't all 29er forks set on 51mm instead of 44-46 and 48mm Manitou?
    Gary Fisher / Trek licensed the Offset as far as Fox's and RS's are concerned, as they I guess paid them for the design tweak.


    Slacker angles = Slower steering and more wheel flop.

    Increased Offset = Faster Steering and less flop.


    So with slacker angles you need increased offset and ofcourse the 2 put together help nicely with toe over lap.

  136. #136
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    So why no other fork came with 51mm offset? Why didn't all 29er forks set on 51mm instead of 44-46 and 48mm Manitou?

  137. #137
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    Quote Originally Posted by Davidcopperfield View Post
    So why no other fork came with 51mm offset? Why didn't all 29er forks set on 51mm instead of 44-46 and 48mm Manitou?

    This has already been answered, see post # 134.

  138. #138
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    Quote Originally Posted by Davidcopperfield View Post
    So why no other fork came with 51mm offset? Why didn't all 29er forks set on 51mm instead of 44-46 and 48mm Manitou?
    Because manufacturers don't share your this one goes to 11 mentality.

  139. #139
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    Do Specialized (woman specific) and Cube (all 29ers) shell out some extra tribute to spec their bikes with 51mm offset forks?

  140. #140
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    Quote Originally Posted by Davidcopperfield View Post
    Do Specialized (woman specific) and Cube (all 29ers) shell out some extra tribute to spec their bikes with 51mm offset forks?




    When is the Unicorn hunt over?

  141. #141
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    Quote Originally Posted by Davidcopperfield View Post
    Do Specialized (woman specific) and Cube (all 29ers) shell out some extra tribute to spec their bikes with 51mm offset forks?
    this is not
    the greatest offset in the world
    oh no
    this is just a tribute

    Tenacious D - Tribute - YouTube

  142. #142
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    Quote Originally Posted by AZ.MTNS View Post
    When is the Unicorn hunt over?
    never ever... EVER!!!

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    Time to stop believing the hype and start doing some science.
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  143. #143
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    Ok so lets say i want to swap my 2008 reba with 38mm offset for a current reba with offset thats 46mm or whatever it is. Both set at 100mm does this speed up my steering or make it more stable?

  144. #144
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    Quote Originally Posted by vizsladog View Post
    Ok so lets say i want to swap my 2008 reba with 38mm offset for a current reba with offset thats 46mm or whatever it is. Both set at 100mm does this speed up my steering or make it more stable?
    Makes handling speed up (shortens trail, decreases wheel flop, increases wheel base).

  145. #145
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    Manitou offers now 51mm offset forks alongside 48mm, which is very strange just 3mm difference. Why not jumpting to 55mm? Also Cannondale offers 53mm on Triggers 29.

    Why haven't the manufacturers begun with 51-5mm in the first place? What do we need 44 and 46mm offsets for? Long travel 29ers with fox 34 and 44mm may feel sluggish.

  146. #146
    mnt bike laws of physics
    Reputation: yogiprophet's Avatar
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    Cannondale's new 29er specific 130mm travel Supermax PBR has an offset of 60mm.
    Am wondering how that is going to feel.

  147. #147
    mtbr member
    Reputation: Davidcopperfield's Avatar
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    How come that noe g2 forks are available for others to be installed on bikes? For instance Ibis Ripley or small Specialized women's frames?

    Will the forks be after-market- available?

  148. #148
    Here, diagonally!
    Reputation: JACKL's Avatar
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    Got me! I read the whole first page before I saw that the thread started in 2007.

    G2 forks? I'm happy that 51mm offset forks are more widely available now, but I don't want a G2 fork.

    Some little known facts about G2 forks:

    It is not known by the general public exactly how the G2 forks are made, but there are reports that they are created in a single step by squirting "G2 Stuff" into a mold.

    If you put a G2 fork on a non-G2 bike, all of your turns will be approximately 6mm too wide, and you will eventually crash.

    When not in use, G2 forks emit a very faint humming noise, and are slightly warm to the touch.

    Magnets are repelled by G2 forks, always and without regard to their orientation.

    G2 forks have been linked to urinary tract infections in cats.

    The good news is that all Fox 34s have a 51mm offset, and the soon-to-be-released Xfusion Trace will also have a 51mm offset. That's appropriate, as these forks have 34mm stanchions and longer travel, so in general will be going on bikes with slacker HTAs.

  149. #149
    mtbr member
    Reputation: Davidcopperfield's Avatar
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    New offset on Trigger 29 - 60mm
    To The Point - Rake and Trail - Pinkbike

  150. #150
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    What that does is allows us to kick the head angle back to a relatively slack, 69 degrees, which if you kept that with a 45-50mmmm rake on a 29er, you would have the most sluggish handling bike in the world.
    <slaps forehead>

    Does this guy design road bikes for a living? A 50mm offset 29er fork gives you almost the same trail as a typical 40mm offset 26". I consider my 68* Yelli w/46mm offset to be damn snappy.

  151. #151
    transmitter~receiver
    Reputation: meltingfeather's Avatar
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    Fork offsets 38-51mm or more and Head Angle issues, let's get it sorted out.

    Quote Originally Posted by Davidcopperfield View Post
    New offset on Trigger 29 - 60mm
    To The Point - Rake and Trail - Pinkbike
    The Gary Fisher approach.
    Quote Originally Posted by pvd
    Time to stop believing the hype and start doing some science.
    29er Tire Weight Database

  152. #152
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    Quote Originally Posted by meltingfeather View Post
    The Gary Fisher approach.
    I was going to say the Spinal Tap approach.

  153. #153
    beater
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    Quote Originally Posted by car_nut View Post
    <slaps forehead>

    Does this guy design road bikes for a living? A 50mm offset 29er fork gives you almost the same trail as a typical 40mm offset 26". I consider my 68* Yelli w/46mm offset to be damn snappy.
    I read that piece when PB first posted it, and I had the same thought.

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