Results 1 to 23 of 23

Thread: Headpost offset

  1. #1
    mtbr member
    Reputation:
    Join Date
    Jan 2013
    Posts
    208

    Headpost offset

    Maybe wrong terminology. I'm tempted to call it "caster angle offset." Or "effective caster angle."

    These newer bikes (last few years) seem to have all sorts of variation.

    But why do some bikes have the offset? Is this the category of "trail" as opposed to "cross-country?" Or "all mountain?"

    I was test-riding a friend's for the first time and, compared to my straight hard tail, the headpost offset was almost impossible to ride!

    It's like a Harley cruiser compared to my Kawasaki Ninja.

  2. #2
    dru
    dru is offline
    mtbr member
    Reputation:
    Join Date
    Sep 2006
    Posts
    2,636
    I'm guessing you are referring to head tube angle, or head angle. In motorcycle and car terms this is known as 'rake', or steering angle.

    Trail is another factor to consider but is somewhat fixed by the fork manufacturers since most forks for a given size run the same amount of offset.

    I agree with what you are saying btw.

    I think these slack bikes are being over marketed. They have a place for sure, but that place is limited to high speeds, downhills, 4X, and dirt jumping....

    (that's a few places, isn't it?)

    Drew
    occasional cyclist

  3. #3
    mtbr member
    Reputation:
    Join Date
    Jan 2013
    Posts
    208
    So high speeds, downhills, dirt jumping...

    Does that mean the head tube offset helps with riding stability? On dirt!?

    It still doesn't make sense to me because the steeper rake of a sport bike motorcycle, for exmaple, is better for tossing left and right compared to cruiser (slack bike?).

  4. #4
    dru
    dru is offline
    mtbr member
    Reputation:
    Join Date
    Sep 2006
    Posts
    2,636
    The steeper rake is unstable......

    Take a look at a drag motorcycle or a bonneville racer and you'll see what I mean.

    These machines use slacker head angles so the rider doesn't die when breaking the sound barrier.

    Sport bikes are designed to turn. Many are quite twitchy when going fast. Watch any road race and you'll see them shaking the bars, despite steering dampers.

    A few years before I road-raced, the 1st generation GSXRs were known to shake at high speed, and most riders learned to adapt and ignore this.

    My Gamma would shake coming out of only one corner and only in 3rd gear, otherwise it was rock solid luckily for me.

    As for bicycles, for XC riding in slow speed tight stuff steep head angles are what you want, at the expense of stability when going fast.

    Drew
    occasional cyclist

  5. #5
    Nouveau Retrogrouch SuperModerator
    Reputation: shiggy's Avatar
    Join Date
    Dec 1998
    Posts
    47,288

    Headpost offset

    Quote Originally Posted by dru View Post
    The steeper rake is unstable......

    Take a look at a drag motorcycle or a bonneville racer and you'll see what I mean.

    These machines use slacker head angles so the rider doesn't die when breaking the sound barrier.

    Sport bikes are designed to turn. Many are quite twitchy when going fast. Watch any road race and you'll see them shaking the bars, despite steering dampers.

    A few years before I road-raced, the 1st generation GSXRs were known to shake at high speed, and most riders learned to adapt and ignore this.

    My Gamma would shake coming out of only one corner and only in 3rd gear, otherwise it was rock solid luckily for me.

    As for bicycles, for XC riding in slow speed tight stuff steep head angles are what you want, at the expense of stability when going fast.

    Drew
    There is much more to it than just head tube angle. HTA, fork offset, front center, wheel base, stem length are all factors.

    Too slack can be as unstable as too steep.

    I have ridden fairly slack mtbs that are terrible at speed and steep bikes that are downhill rockets.
    mtbtires.com
    The trouble with common sense is it is no longer common

  6. #6
    dru
    dru is offline
    mtbr member
    Reputation:
    Join Date
    Sep 2006
    Posts
    2,636
    True no doubt Shiggy, but what I'm saying is likely accurate for most bicycles.

    As for motorcycles I was making an observation that is obvious. There is little in common between a Top Fuel Harley and a MotoGP bike with respect to HA.

    Unlike bicycle fork offset which is 'set' by mass production across brands (unless you are building your own/custom rigid), different offset triple clamps are available for MCs from the aftermarket.

    My brother's 1992 CBR900RR was overly twitchy at high speed and at some point different triple clamps became available from the aftermarket as a solution. Adjustable head angles weren't available back then on street machines.

    Drew
    occasional cyclist

  7. #7
    mtbr member
    Reputation:
    Join Date
    Jan 2013
    Posts
    208
    Quote Originally Posted by dru View Post

    Unlike bicycle fork offset which is 'set' by mass production across brands ...

    Drew
    So is this the definition of either of the "cross country" or "trail" or "all mountain" categories?

    Maybe I've gotten too used to my solid tail geometry, but this particular odd feel is the other thing that has kept me from getting a full suspension bike. Or maybe all the ones I've test-ridden were the wrong type (category).

  8. #8
    dru
    dru is offline
    mtbr member
    Reputation:
    Join Date
    Sep 2006
    Posts
    2,636
    Quote Originally Posted by solidass
    So is this the definition of either of the "cross country" or "trail" or "all mountain" categories?

    Maybe I've gotten too used to my solid tail geometry, but this particular odd feel is the other thing that has kept me from getting a full suspension bike. Or maybe all the ones I've test-ridden were the wrong type (category).
    Not quite sure what you are asking. Offset is the distance the front axle dropouts sit relative to the steering axis, measured parallel to that axis. Head angle and offset combine to produce a certain about of 'trail' which is how far behind the steering axis the contact point of the tire sits.

    The categories you listed are about bike type and riding style more than anything else. In the order you listed them each of the bikes is burlier and has more travel.

    Drew
    occasional cyclist

  9. #9
    dru
    dru is offline
    mtbr member
    Reputation:
    Join Date
    Sep 2006
    Posts
    2,636
    Quote Originally Posted by dru

    Unlike bicycle fork offset which is 'set' by mass production across brands (unless you are building your own/custom rigid),
    Apologies needed Shiggy! There's quite a range of offsets available now, unlike the 90's where it seemed everything had 39 mm of offset...

    http://http://forums.mtbr.com/shocks...ks-736488.html

    my bad!

    Drew
    occasional cyclist

  10. #10
    Nouveau Retrogrouch SuperModerator
    Reputation: shiggy's Avatar
    Join Date
    Dec 1998
    Posts
    47,288

    Headpost offset

    Quote Originally Posted by dru View Post
    Apologies needed Shiggy! There's quite a range of offsets available now, unlike the 90's where it seemed everything had 39 mm of offset...

    http://http://forums.mtbr.com/shocks...ks-736488.html

    my bad!

    Drew
    The 39 mm offset was common, but not the only option. Most Marzocchis used 45mm. Rigid forks were still offered with many offsets, especially if custom.
    For me, the slacker HTA bikes using the same short fork offsets and short stems creates vague steering that wanders and does not want to turn. Like an unloaded wheelbarrow in sand.
    mtbtires.com
    The trouble with common sense is it is no longer common

  11. #11
    mtbr member
    Reputation:
    Join Date
    Jan 2013
    Posts
    208
    Quote Originally Posted by dru View Post
    Not quite sure what you are asking...
    The general oddity is the feel. So regardless of whether it's just a steeper/shallower rake angle or an offset or both, I'm finding the difference in feel (compared to my solid tail) quite stark on some full suspension bikes, but not others. Every bike maker offers more than one type of full suspension bike.

    And while they're all roughly similar in size and appearance, I was starting to think it has to be also the type of riding or trails for which they're designed. Such as the categories of "trail riding" or "all mountain" etc.

    Surely there are other factors that define each riding category, but this general odd feel of the head angle, to me, is huge.

    Because it's hard to think that "slacker" angles are just for faster cruising speeds.

    Don't all mountain bikes go downhill fast? Or riders wanting to go fast?

    "Oh, I like the slacker angle because I want to climb uphill SLOWLY."

    Err... I don't think so.

  12. #12
    dru
    dru is offline
    mtbr member
    Reputation:
    Join Date
    Sep 2006
    Posts
    2,636
    Because it's hard to think that "slacker" angles are just for faster cruising speeds.
    Well, that's because they aren't. Slack HA's also help in really rough stuff and going downhill.

    They don't help when going up hill because climbing by its very nature is a slow speed affair. With 1/3 of a HP at best, we aren't exactly a motocross engine are we?

    Drew
    occasional cyclist

  13. #13
    mtbr member
    Reputation:
    Join Date
    Jan 2013
    Posts
    208
    Quote Originally Posted by dru View Post
    Slack HA's also help in really rough stuff and going downhill...
    To clarify my comments about the "trail" and "all mountain" category of bikes, the contrary viewpoint might help if slacker head angles (with or without offsets whatever) are better for "high speeds, downhills, 4X, and dirt jumping..." and "also help in really rough stuff and going downhill..."

    Then why doesn't EVERY mountain bike have it? Why isn't the entire off-road bicycling community embracing it? Why aren't all bikes made with slacker head angles?

    Especially if "the steeper rake is unstable..."

    You seem to be singing the praises in every way, yet say "I think these slack bikes are being over marketed. They have a place for sure..."

    Not quite sure what's your point.

  14. #14
    dru
    dru is offline
    mtbr member
    Reputation:
    Join Date
    Sep 2006
    Posts
    2,636
    I'm not singing their praises at all, except for the specific applications at which they excel.

    For the riding I do most would suck!

    My 29er has a 72 deg HA and my 26er has a 70. For XC, medium quick steering.

    I ride relatively slow very tight single-track where the average speed is 12 mph/18kmh for very fast riders on one of the faster trails. The slow stuff I ride at Puslinch would be well under 10 mph/16 kmh.

    Provincial masters expert champions average XC speeds are 18 to 22 kmh here depending on the course. That's not fast and slack angles aren't needed at all. Masters expert aint slow as far as XC goes btw.

    Drew
    occasional cyclist

  15. #15
    mtbr member
    Reputation:
    Join Date
    Jan 2013
    Posts
    208
    Quote Originally Posted by dru View Post
    I'm not singing their praises at all, except for the specific applications at which they excel...

    Drew
    Not to belabor the point, but you seem to be confusing Consequence with Desire.

    The CONSEQUENCE of your tight single track venue is slow speed. But the DESIRE of every rider is to go faster, safer, smoother, have more fun.

    Is there ever a desire to go slower?

    So while you may think you're not singing the praises (of steeper head angles), you're not categorizing the type of riding that apply either. You even mention "provincial masters expert champions" which I assume are racers. Racers who desire to go slower?!

    You just say that you think slacker bikes are over marketed as if in all of mountain biking, there's never any "high speeds, downhills, 4X, and dirt jumping... really rough stuff and going downhill..."

    I still have no idea what that means without the category of riding.

  16. #16
    dru
    dru is offline
    mtbr member
    Reputation:
    Join Date
    Sep 2006
    Posts
    2,636
    So while you may think you're not singing the praises (of steeper head angles), you're not categorizing the type of riding that apply either.
    I have: high speeds, downhills, 4X, and dirt jumping. If you are doing that type of riding a slacker bike will be your choice.

    Is there ever a desire to go slower?
    Obviously, for a racer, no! But the type of course affects how fast you can go and a slacker bike is more of a workload and is generally slower in the tight stuff.

    You even mention "provincial masters expert champions" which I assume are racers.
    I mentioned them because they are fast as hell in the discipline of XC racing, yet the average speed they are going is actually really slow.

    You just say that you think slacker bikes are over marketed as if in all of mountain biking, there's never any "high speeds, downhills, 4X, and dirt jumping... really rough stuff and going downhill..."
    The marketers are doing what they do best, shooting/filming guys going ultra fast/hucking/freeriding on the west coast mostly because sensational riding sells much better than seeing guys riding along at 20 kmh on single track.

    Most of us just aren't that extreme or good for that matter and probably aren't doing that type of riding most/any of the time.

    I suspect that many of us ride single track instead and would have to be very fast indeed to be pushing an average speed of 20 kmh for an hour or so. We certainly don't need slack geometry to do that.

    Drew
    occasional cyclist

  17. #17
    mtbr member
    Reputation:
    Join Date
    Jan 2013
    Posts
    208
    Quote Originally Posted by dru View Post
    The marketers are doing what they do best...

    Drew
    You're also marketing/ advertising/ advocating it quite well right here!

    I want to race the tight single-track at high speeds, going downhill, 5x even 6x, doing dirt jumping when there are jumps, and generally tackle the really rough stuff with the slacker head angle!

    Who wouldn't!

  18. #18
    dru
    dru is offline
    mtbr member
    Reputation:
    Join Date
    Sep 2006
    Posts
    2,636
    Buy a slack bike then. But you might find it a bear to turn in the tight stuff and won't necessarily like its climbing manners. That's the price you pay.

    Drew
    occasional cyclist

  19. #19
    Nouveau Retrogrouch SuperModerator
    Reputation: shiggy's Avatar
    Join Date
    Dec 1998
    Posts
    47,288

    Headpost offset

    Quote Originally Posted by solidass View Post
    You're also marketing/ advertising/ advocating it quite well right here!

    I want to race the tight single-track at high speeds, going downhill, 5x even 6x, doing dirt jumping when there are jumps, and generally tackle the really rough stuff with the slacker head angle!

    Who wouldn't!
    I am wondering why you have now become defensive of the slack bikes after dising them in your opening post?

    You certainly do not understand the different riding disciplines any better than the geometry terminology.
    mtbtires.com
    The trouble with common sense is it is no longer common

  20. #20
    mtbr member
    Reputation:
    Join Date
    Jan 2013
    Posts
    208
    Quote Originally Posted by dru View Post
    Buy a slack bike then. But you might find it a bear to turn in the tight stuff and won't necessarily like its climbing manners. That's the price you pay.

    Drew
    It seems you finally understand my point! But why would I want to buy a bike that's a bear to turn in the tight stuff? Why would anybody?

    And the mystery continues...

  21. #21
    dru
    dru is offline
    mtbr member
    Reputation:
    Join Date
    Sep 2006
    Posts
    2,636
    I got your point from your 1st post. You are talking about a broad subject here. Bike geometry is a trade off.

    But why would I want to buy a bike that's a bear to turn in the tight stuff?
    You'd buy such a bike if your desire for high speed/rough stuff stability outweighed your desire for good low speed handling.

    Drew
    occasional cyclist

  22. #22
    mtbr member
    Reputation:
    Join Date
    Jan 2013
    Posts
    208
    Quote Originally Posted by dru View Post
    You'd buy such a bike if your desire for high speed/rough stuff stability outweighed your desire for good low speed handling.

    Drew
    That's probably as close as we'll get. And it's a good rewording into an answer!

    Problem is, it's all relative, isn't it? What biker riding on any dirt wouldn't want high speed/ rough stuff stability? And how low is low as the speed that any mtn biker would want to trade off?

    And if you think we're talking about predicting personal preferences, foreseeing trail conditions, or limiting our riding style, there's hopefully a better way to describe it.

    But it's probably best left as a mystery.

  23. #23
    Nouveau Retrogrouch SuperModerator
    Reputation: shiggy's Avatar
    Join Date
    Dec 1998
    Posts
    47,288

    Headpost offset

    Quote Originally Posted by solidass View Post
    That's probably as close as we'll get. And it's a good rewording into an answer!

    Problem is, it's all relative, isn't it? What biker riding on any dirt wouldn't want high speed/ rough stuff stability? And how low is low as the speed that any mtn biker would want to trade off?

    And if you think we're talking about predicting personal preferences, foreseeing trail conditions, or limiting our riding style, there's hopefully a better way to describe it.

    But it's probably best left as a mystery.
    I know what it takes for me to have a bike with agility, responsiveness, and stability in the rough at speed.

    Not just HTA and fork offset. General setup and weight distribution matter, too. With the current geometry fashions few, if any, production frames are acceptable for me.
    mtbtires.com
    The trouble with common sense is it is no longer common

Similar Threads

  1. Offset Bushings, Yay or Nay??
    By curbhuck in forum Ibis
    Replies: 9
    Last Post: 3 Days Ago, 12:05 AM
  2. offset Large Marge to "non-offset" turing?
    By toezter in forum Wheels and Tires
    Replies: 0
    Last Post: 02-06-2013, 06:15 PM
  3. Replies: 3
    Last Post: 09-06-2012, 05:46 PM
  4. Difference between offset and zero offset seatpost
    By D3NN15M in forum Beginner's Corner
    Replies: 3
    Last Post: 06-28-2011, 07:39 PM
  5. G2 Offset
    By bit_lizard in forum 29er Bikes
    Replies: 7
    Last Post: 05-19-2011, 11:39 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •