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  1. #1
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    29ers and different fork offsets

    I am trying to educate myself on fork offset relation to bike handling.
    What I have gathered so far is shorter offset increases trail and supposedly making the stearing slower.
    The thing is with shorter offset the WB gets shorter as well, wouldn't the shorter wb negate the slower steering of a longer trail?

    How does the different offset # effects bikes with different HTAs?
    What was the real life observation going to different offsets?
    I am decing between 46mm and 51mm 140mm frok for a SC Hightower.

    Any info is appropriated.

    Some info here
    Fork offset: what is it and how does it affect your riding? - MBR
    Fork offset: what is it and how does it affect your riding? - MBR

    Transition Introduces Speed Balanced Geometry | BIKE Magazine


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  2. #2
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    Grab a long object like a ruler, hold it by one end and move it only a half inch. Now grab it in the middle and do the same. It's easier to be exact when grabbing the middle but quicker when holding the end. Now how does this relate?

    The 51mm offset is like holding the end of the ruler. It moves more quickly and can be over sensitive to some at higher speeds, making you over correct and feel unstable.

    The 46mm or 42mm offset will be slower but more exact. The 51mm helps in tight twisty trails, avoiding near misses with trees and stuff. If you're going over 20mph a lot, you might prefer the 46mm.

  3. #3
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    Quote Originally Posted by Cerberus75 View Post
    Grab a long object like a ruler, hold it by one end and move it only a half inch. Now grab it in the middle and do the same. It's easier to be exact when grabbing the middle but quicker when holding the end. Now how does this relate?

    The 51mm offset is like holding the end of the ruler. It moves more quickly and can be over sensitive to some at higher speeds, making you over correct and feel unstable.

    The 46mm or 42mm offset will be slower but more exact. The 51mm helps in tight twisty trails, avoiding near misses with trees and stuff. If you're going over 20mph a lot, you might prefer the 46mm.
    How about the decreased WB with Shorter offset? Not too much of a difference to effect the handling?

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  4. #4
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    I could not notice a noticeable difference in going from 46 to 42 on my reign. As you may or may not know they spec a special 46noffset for their bikes. That being said I also went up in travel from 160 to 180 so that added Geo differences there as well.

    After that being said! My hightower with a 51mm offset fork feels great. I've never had snapping issues when turning sharply, I don't find it so sensitive that it steerse of line. If anything due to the straight line trucking 29ers like to do it may help equalize that

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  5. #5
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    Quote Originally Posted by TamiJean View Post
    I could not notice a noticeable difference in going from 46 to 42 on my reign. As you may or may not know they spec a special 46noffset for their bikes. That being said I also went up in travel from 160 to 180 so that added Geo differences there as well.

    After that being said! My hightower with a 51mm offset fork feels great. I've never had snapping issues when turning sharply, I don't find it so sensitive that it steerse of line. If anything due to the straight line trucking 29ers like to do it may help equalize that

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    The thing is, the new trend set by Mojos Chris Porter and now Transition bikes implementing the same strategy is to decrease offset and those bikes are pretty slack at <64°...
    The slacker, the less twitchy and slow steering they are and shortening the offset will emphasize it even more.

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  6. #6
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    Quote Originally Posted by jazzanova View Post
    The thing is, the new trend set by Mojos Chris Porter and now Transition bikes implementing the same strategy is to decrease offset and those bikes are pretty slack at <64°...
    The slacker, the less twitchy and slow steering they are and shortening the offset will emphasize it even more.

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    You could spin circles in your brain trying to understand theories and how they work. The best application is to try it real world. What one likes is not what another will. In the past 2 years I've been on 2 different wheel sizes and 3 different offsets. My reign with a 180mm fork and 42 offset would be about as slack and stable in theory, yet my hightower still feels very stable but also controllable steeper with more offset.

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  7. #7
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    Quote Originally Posted by TamiJean View Post
    You could spin circles in your brain trying to understand theories and how they work. The best application is to try it real world. What one likes is not what another will. In the past 2 years I've been on 2 different wheel sizes and 3 different offsets. My reign with a 180mm fork and 42 offset would be about as slack and stable in theory, yet my hightower still feels very stable but also controllable steeper with more offset.

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    Thanks.
    How about the offset to stem relation theory? Longer offsets are paired better with longer stems...

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  8. #8
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    Meh, you are poking at things I could care less about. My theory will always be if it feels right then run with it. I've used a 50 on all my bikes. And set up always lower stack with a higher rise bar to keep reach at it's longest. I struggled with front end weight early on so I never went shorter. I "feel" like I could go shorter on my HT since it's a tad steeper and my weight is more balanced between front and rear but I don't care enough to try it yet.

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  9. #9
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    Quote Originally Posted by TamiJean View Post
    Meh, you are poking at things I could care less about. My theory will always be if it feels right then run with it. I've used a 50 on all my bikes. And set up always lower stack with a higher rise bar to keep reach at it's longest. I struggled with front end weight early on so I never went shorter. I "feel" like I could go shorter on my HT since it's a tad steeper and my weight is more balanced between front and rear but I don't care enough to try it yet.

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    I am about to rent a L HT.
    I have already tried a medium and will need to use at least a 50mm stem.
    On the L it is most likely going to be a 32mm.
    I am on L Nomad3 with 40mm stem now. L N3 438mm reach, L HT 450mm.
    5'8.5" 31"inseam
    Will see how it goes.

    I don't mind the longer reach/WB of a larger bike, as long as I am comfortable while seated, which is a result of ETT and STA more than anything.

    Thanks for the riser bars tip to keep the reach long...

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  10. #10
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    Quote Originally Posted by jazzanova View Post
    How about the decreased WB with Shorter offset? Not too much of a difference to effect the handling?

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    Not enough to notice.

  11. #11
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    I like 51mm on my 29er fork... My 650b mule has 46mm which doesn't feel too strange.

    I demo'd a Trek Remedy 8 w/ 42mm offset & it felt like the fork was going to run away, underneath me!!

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    Quote Originally Posted by targnik View Post
    I like 51mm on my 29er fork... My 650b mule has 46mm which doesn't feel too strange.

    I demo'd a Trek Remedy 8 w/ 42mm offset & it felt like the fork was going to run away, underneath me!!

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    You do know that w/ less offset, the fork/front wheel is more tucked up under the head tube, yeah?

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    To use a 35mm stem on my bike I want 780mm bars. I'm inbetween sizes. If I were to size up I would need 760 bars and this would feel to quick, so then I would reduce offset to change this. Or if I rode in areas that I'm going over 25mph often.

  14. #14
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    Less offset will slow down the steering and make the bike more stable even with a shorter wheels base. Your stem should also be matched to your offset. So if you have a 51 offset a 50 stem will match your wheel arc.
    If you are bombing steep descents at mach speed then a 46 would be better but will give up flat land nimbleness.
    Everything is a compromise from bar width, stem height/length, fork offset, hta.......
    Changing these will fine tune the feel of the bike to your style and the terrain you ride.

    The trend for handling is:
    more offset = faster
    shorter stem = faster
    slack HTA = slower
    wider bars = slower

    This gives you a longer bike with increased wheelbase that is way more stable and capable, but with fast steering.

  15. #15
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    Quote Originally Posted by alexbn921 View Post
    Less offset will slow down the steering and make the bike more stable even with a shorter wheels base. Your stem should also be matched to your offset. So if you have a 51 offset a 50 stem will match your wheel arc.
    If you are bombing steep descents at mach speed then a 46 would be better but will give up flat land nimbleness.
    Everything is a compromise from bar width, stem height/length, fork offset, hta.......
    Changing these will fine tune the feel of the bike to your style and the terrain you ride.

    The trend for handling is:
    more offset = faster
    shorter stem = faster
    slack HTA = slower
    wider bars = slower

    This gives you a longer bike with increased wheelbase that is way more stable and capable, but with fast steering.
    Thanks.
    There have been opposite trends regarding to offset though.
    Like Chris Porter from Mojo with his Nicolai or the new Transition 29er (not released yet), which has 64° HT combined with shorter offset...
    I believe Porter has been experimenting with angles around 62°, longer CS, steeep ST and obviously very long WB.

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  16. #16
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    Great read about geometry and bike handling from the G.O.A.T.

    https://www.pinkbike.com/news/behind...-v10-2016.html

    We found that anything under 63-degrees, the bike just doesn't want to turn, it just wants to go in a straight line," but more on that later. Adding a shorter stem would help, at least in the short term, but at the speeds encountered on the World Cup circuit, it also made the front feel 'nervous,' and Marshy and Greg determined that a slacker head angle detrimentally affected suspension performance. "Past 63-degrees, forks flex more than they compress," says Marshy.

  17. #17
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    51mm offset is also a bit dated back when people were running 80-120mm stems on 29ers. The trend of 50mm or less stems quickens steering so you can get away with a lower offset.
    Everyone is entitled to my opinion.

  18. #18
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    Quote Originally Posted by Pau11y View Post
    You do know that w/ less offset, the fork/front wheel is more tucked up under the head tube, yeah?
    You don't say...

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  19. #19
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    Another good article about transitions approach
    http://m.vitalmtb.com/features/Speed...ain-Bikes,1861

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    Quote Originally Posted by targnik View Post
    You don't say...

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    Just trying to figure out your insanity of how a more tucked in front end can "run away" from you

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  21. #21
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    I have been thinking about this and reading up on the subject of bike handling, trying to nail down my setup. I come for car road racing and have always been a suspension guy.

    My Tallboy 3 is long(505 reach). This fits me perfectly with a 50mm -6 stem and 20mm riser 760 bars. It's amazing to finally have a bike that I feel "in", and the confidence on rough terrain is off the carts. Now that I'm pushing the bike to it's limits I keep losing the front end before the the back. No matter how I position myself the front end wants to tuck because it just doesn't have enough weight on it. I slammed the bars as low as they could go and that made things better. I'm already running a 100mm drop from the saddle and can't go lower without buying new bars.

    Part of the problem that I'm having is that the Small is 100mm shorter than the XXL, but the rear end is identical. I need longer chain stays to balance out the longer front. Since I can't make the back longer I need to make my reach longer(stem), my bars lower/wider or my front wheelbase shorter.

    Here's where offset comes in, if I swap out the fork uppers to a 27.5 set with the 44mm offset I will shorten my front by by 7mm. This will increase trail, stabilizing the bike and slowing down the seering.

    You may say that I should have got a smaller bike with a longer stem, but would have come with it's own set of compromises. I was swapping between my XL/XXL bikes this weekend and I could really feel the differences in characteristics.

    I feel that more 29er trail bikes are going to specced with shorter offset forks in the future. As the front gets longer you need balance the speed of the steering with the weight distribution. For riders on small to large frames a 51 might make more sense. Until XL and XXL get longer rears, shorter offsets might make up for the imbalance.

    Fox doesn't make a sub 51mm 29er fork so i'm going to frankenstein my own and report back.
    FYI I'm running 130mm at the moment with a 2.5 DHF up front and a 2.35 Nobby Nic in the rear.

  22. #22
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    If only fork manufacturers will design their forks to have an adjustable offset... That way people could experiment and find what works for them. That and they need to design frames to have multiple headangle options.
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  23. #23
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    Not particularly about offset, but still a great article about some new geo trends.

    http://enduro-mtb.com/en/thegeometryaffair-part-2/

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    Hi Jazznova,

    So, SC gives you the option of offset in buying new?

    If so, I may go that way.

    I am a fan of 44-46mm offset on newer 29er geo, but can't find any options!

    51 just feels too twitchy for me.

    Also, love to hear the results of alexbn921's test, I would love a tallboy 3 29er w/ 46mm offset 29er fork.

    Thx!
    Holiday

  25. #25
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    I rolled my eyes at their marketing. My opinion is predicated on my experience.

    I was on a 130mm with 46mm offset, and then changed to a 140mm with 51mm offset and it was immediately noticeable, and so good in every way. I couldn't believe I didn't do that sooner. I went from the Rockshox Revelation RCT3 to a DVO Diamond so of course the fork itself made a big difference, but the way it changed the steering and how much more grip I felt, I instantly found myself pushing my bike harder and faster..especially through corners!

    Worth every penny IMO, but that was my experience.
    Ibis Ripley LS
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  26. #26
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    Quote Originally Posted by dubdryver View Post
    I rolled my eyes at their marketing. My opinion is predicated on my experience.

    I was on a 130mm with 46mm offset, and then changed to a 140mm with 51mm offset and it was immediately noticeable, and so good in every way. I couldn't believe I didn't do that sooner. I went from the Rockshox Revelation RCT3 to a DVO Diamond so of course the fork itself made a big difference, but the way it changed the steering and how much more grip I felt, I instantly found myself pushing my bike harder and faster..especially through corners!

    Worth every penny IMO, but that was my experience.
    What size bike are you riding? Offset is size specific.

  27. #27
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    Quote Originally Posted by alexbn921 View Post
    What size bike are you riding? Offset is size specific.
    Sizing deviates from brand to brand. I'm on an Ibis Ripley LS.

    I understand the need to correct where the wheel makes contact on the ground to ensure proper grip and leverage, and offset is certainly the way to do that, but that is exactly what "more offset" does by reducing the trail by placing the leverage under the axle instead of in front of it.

    Or you can adjust the or where the fork legs are by the offset at the fork crown. Nobody talks about it, but there is offset there. If you look at the changes on their bikes....you see less crown offset, and no change on the dropouts.
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    The tire is always going to leverage under the axle as that's where all tires contact the ground. Increasing the offset will increase your mechanical advantage over the self centering effect.

    Fork crown or axle offsets have the exact same effect. Doesn't matter how you achieve it. My head shock has bent lower legs to get the offset. I'm changing my CSU to reduce the offset at the crown.

    Ibis makes great bikes, but they are short. If your riding a medium bike with a longer stem then you probably have to much weight on the front wheel and increasing offset will balance the bike better for you.
    Fyi going from a 130/46 to a 140/51 only changed your trail by less than 1mm. You did get a much longer bike and you like it. It was the right step for your style and bike.

  29. #29
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    Quote Originally Posted by dubdryver View Post
    I rolled my eyes at their marketing. My opinion is predicated on my experience.

    I was on a 130mm with 46mm offset, and then changed to a 140mm with 51mm offset and it was immediately noticeable, and so good in every way. I couldn't believe I didn't do that sooner. I went from the Rockshox Revelation RCT3 to a DVO Diamond so of course the fork itself made a big difference, but the way it changed the steering and how much more grip I felt, I instantly found myself pushing my bike harder and faster..especially through corners!

    Worth every penny IMO, but that was my experience.
    The difference is more than likely due to either the HTA or more likely just the fork and it's performance than trail. Trail was marginally affected in your case as alexbn921 stated.
    Everyone is entitled to my opinion.

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