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Fork offset

Discussion in 'Downhill & Freeride' started by FlipSide, Mar 21, 2018.

  1. FlipSide

    FlipSide Monkey

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    It is not unreasonable to think I will upgrade my bike in the next few months and there are fairly high chances I will go for a custom build, as I always did for the past 16 years.

    The new 2019 Lyrik RC2 is looking good to me if I go all out and move from 26" to 27.5" or 29". I just saw they are coming with different fork offset. Which one do I want for All-Mountain riding? What I ride is really a mix of everything, from lift-assisted rides with high-speed and technical stuff, to pure XC sections with important pedaling and climbing.

    From what I understand, greater offset leads to a quicker handling. Based on this, I am thinking that for the riding I do (mix of everything), it would either make sense to:
    - put a fork with more offset if I go for a slack enduro frame (ex.: Devinci Spartan) to make the bike more lively for the XC parts;
    - put a fork with smaller offset on an AM frame (ex.: Devinci Troy) to make the bike more stable at speed;

    Do I get this right? Should I just stop overthinking, suck it up for the climbs and go for the smaller offset no matter what and make sure sure my rips as much as possible for the fun parts?

    Thanks! :monkey:
     

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  2. buckoW

    buckoW Turbo Monkey

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    Recently, I'm really liking the low offset forks. I went the other way for a few years and even had 2 sets of 40 crowns with more offset for testing.One was angled and one was offset. It does make the steering feel lighter and the bike has less flop BUT the front tire is way less planted and steps out a lot easier. In addition, a flat corner with a high offset fork is much harder to ride fast than with low offset. It's almost like your contact patch is windshield wiper-ing around rather than pivoting in a flat corner (that probably makes no sense but at least I tried to articulate the feeling). Conclusion, I can ride harder and more confident with less offset.
     
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  3. Sandwich

    Sandwich just shake your rump
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    :stupid:

    in my experience, low offset forks handle better in almost all conditions, and I struggle to understand why anybody would want to "liven up" your steering in an era of super slack head angles. The window wipering analogy is a good one; I don't fully understand trail and all that, but high offset forks have always felt floppier to me (tank slapperier?), and shortening offset allowed me to more confidently put the wheel where I want it.
     
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  4. djjohnr

    djjohnr Turbo Monkey

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    I have two forks with the same axle-to-crown distance but with different offsets - 44 and 46mm. 2 mm doesn't sound like much difference, but it's pretty apparent at times. It's tough to isolate the offset as a variable off-road since one is a single crown air fork and the other is a dual crown coil, but on pavement the shorter offset fork feels like it's response to steering input is more direct/lively. @buckoW 's windshield wiper analogy for the longer offset feel is pretty apt. I suspect the longer offset fork is a touch more resistant to getting knocked off line, but it's hard to say for sure it's the offset since the forks are so different.
     
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  5. thad

    thad Monkey

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    There seem to be two trains of thought on this:

    https://www.transitionbikes.com/SBG.cfm
    Transition has their SBG, where they had both Fox and Rockshox make them custom shorter offset forks, in conjunction with longer reach, slacker head angle, shorter 35mm stems.

    But then, there's the new boxxer 29" with longer offset...
     
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  6. Gary

    Gary "S" is for "neo-luddite"

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    Do you struggle to understand people who have perfectly reasonable but different preferences to yourself in any other aspects of every day life?
     
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  7. ChrisRobin

    ChrisRobin Turbo Monkey

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    FWIW, I used to have a 51mm Fox 36 29er. I found if you ran a short stem, it just didn't handle well. The wheel felt like it deflected everywhere. I found a 27.5 CSU (don't remember if they're 44 or 46mm) and I found the wheel tracked better while climbing technical stuff. Going back to that short stem felt great too.
     
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  8. HAB

    HAB Chelsea from Seattle

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    Yeah, I'm in the shorter camp too. I've got a couple 650b 36s with 26 CSUS (40mm offset) and I've got CAD drawn up to make a 37mm offset crown for a 26 40 that I really need to get around to getting made
     
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  9. roflbox

    roflbox Turbo Monkey

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    When I was in Moab, I rented a medium sentinel, what they did with the fork offset and geo was pretty nice, I am quite a fan of that bike.
     
  10. Sandwich

    Sandwich just shake your rump
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    oh gary
    I understand the goal of 51mm. I get why people would want a zippy handling bike. It's the same reason I keep my bike in the "high" setting rather than the slack setting, (despite anything under 59* being unrideable on ridemonkey.) What I don't agree with and cannot see the logic of is that offset is really a shitty way of achieving something similar to adjusting head angle (despite what gary fisher and mtbr says). I haven't felt a bike with higher offset that I've liked at any speed and wheelsize, and when given the option, I'd rather stick with a steeper head angle and shorter trail to keep steering lively, or a slack head angle and short offset to keep steering stable, as the connection between hands and wheel is adversely affected by increased offset.
     
  11. Gary

    Gary "S" is for "neo-luddite"

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    Oh sammich
    it's not really as simple as that.
    Riding style, wheelsize, wheelbase, reach and stem length stem all play a part too.
    But even so. You know by now I don't go with what's fashionable. I go with what I like the feel of for the riding I prefer to do. If that happens to be a different to someone elses ideals. i don't really give a fuck.
     
    #11 -   Mar 23, 2018
    Last edited: Mar 23, 2018
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  12. Udi

    Udi RM Chief Ornithologist: “I Brake for Birds”

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    If you have a choice, you should choose the shorter offset (as most people voted).

    This might be useful if anyone wants to compare the different 36 options, or compare RS to Fox:

    The numbers for the 40 are not exactly the same FYI.

    This article is also interesting:
    https://www.bikeradar.com/mtb/gear/article/pushing-the-limits-of-fork-offset-an-experiment-45343/

    It makes a good point that reducing offset (on a frame/fork combo you're already riding) isn't necessarily better unless your frame sizing is a little on the long side for you already, because it does shorten the wheelbase - which has a far greater impact on handling than reach. A works reach-adjusting cup set could compensate this if needed.
     
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  13. bengxe

    bengxe Monkey

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    I ran my boxxer crowns backwards for a few months last year to try this reduced offset idea. The crowns are offset around 8mm, so reversing them takes the total fork offset from 46mm to 30. I liked what it did to the handling at speed, even with the reduced wheelbase. The only issue was it limited the maximum steering angle, which caused some awkward slow crashes that I otherwise could've ridden out. I've been looking for better low offset options ever since, but the industry seems to be headed in the opposite direction.
     
  14. Olly

    Olly Chimp

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    Are Fox/Rockshox “just” using the CSU from the next wheel size down (ie 26” CSU on the 27.5” SBG fork)?
     
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  15. Floor Tom

    Floor Tom Monkey

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    Yes they are.
     
  16. Flo33

    Flo33 Monkey

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    Could you explain please? I thought the 26 CSU is a lot shorter,



    compared to



    I did my first ride on a recently purchased 650b 36 yesterday and it felt akward compared to my 26 36 Van I used to run with 650b wheels for the best part of a year. Both are 160 mm versions. Is the 26 CSU interchangeable with the 650b lowers, spring and damping cart?
     
  17. Floor Tom

    Floor Tom Monkey

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    Yes it is, the only part that changes is the lowers. On the recent ones anyway, not sure about older models.
     
  18. HAB

    HAB Chelsea from Seattle

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    Yeah I remembered the 26 offset wrong. It's 37mm.

    On the 2015-17 forks the CSU is fully interchangable across wheel sizes. I think that's still true for the 2018s, but they changed the float air spring for 2018 so you can't run a 2015-17 spring in a 2018 CSU, or vice versa. I think the dampers still swap.
     
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  19. Flo33

    Flo33 Monkey

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    I was thinking about crown to axle height, not rake. I didn't even notice the wrong 40/37 number. I'm using a 2015 TALAS RC2, so all good.

    What I found on a quick search doesn't make me happy though, >400 Euros...
    I think I will take the steering angle reducer way.


    Quick calc gives me 10.56 cm lever for the restoring torque with the 650b 44 mm offset fork at 65° headangle, 37 mm 26" fork rake gives a lever of 11.26 cm. A -1.5° reducer leads to a lever of 11.40 cm with the 44 mm rake, which is close to the 37 mm numbers. Bonus: longer wheelbase.
     
    #19 -   Mar 26, 2018
    Last edited: Mar 26, 2018
  20. Happymtb.fr

    Happymtb.fr Monkey

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    You are referring to the trail figure, aren't you ?
     
  21. slyfink

    slyfink Turbo Monkey

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    Interesting thoughts on offset here.

    Of course, this is a "first ride" review of a brand new bike, so lots of things could be clouding his perception, but I thought it interesting nonetheless. And that he finds both positives and negatives is also refreshing. I guess it's a question of weighing both the pros and the cons, and seeing how they mesh with your riding style and preference...
     
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  22. Flo33

    Flo33 Monkey

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    Not exactly, the lever is the distance perpendicular between the steering axle and the vertical line through the contact point of the wheel and the axle. Trail is the horizontally projected distance of this number.
     
    #22 -   Mar 26, 2018
    Last edited: Mar 27, 2018
  23. Happymtb.fr

    Happymtb.fr Monkey

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    Isn't that the mechanical trail then?
    image_aadbfd2d72c11fee7f6e8777a34ac6b1f240f0e3.png
     
  24. Flo33

    Flo33 Monkey

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  25. Kanye West

    Kanye West 220# bag of hacktastic

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    People really need to stop confusing "steering" response/stability/agility with "leaning" response/stability/agility while discussing offset. They are two very different things.
     
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  26. StiHacka

    StiHacka Compensating for something

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    I am leaning towards the same opinion. Thanks for steering this to the right direction.
     
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  27. Flo33

    Flo33 Monkey

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    Hey Hacktastic, who is confusing and why do you think so?
     
  28. Meagann

    Meagann Chimp

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    even due to my poor riding experience I can say that low offset folks are more likely to handle everything mentioned by you
     
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  29. FlipSide

    FlipSide Monkey

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    Thanks to all for your replies, it has been really helpful.

    From what I gathered here and elsewhere, it sounds like lower offset is the new longer reach.
     
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  30. rideit

    rideit Bob the Builder

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    What does a bot say?
     
  31. kidwoo

    kidwoo Celebrating No-Pants Day

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    I like longer offset forks climbing at 4mph. That's the only place I like them. Kinda like bigger wheels.
     
  32. Sandwich

    Sandwich just shake your rump
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    to clarify from earlier, I'm not looking for a zero offset fork, but rather that we've overcorrected in the push to big wheels, and shortening that offset will give us more stability that we used to have with 26" wheels that has gone away a bit with big ones and high offset.
     
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  33. Gary

    Gary "S" is for "neo-luddite"

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    Patience son.

    EVENBIGGERWHEELZ™ will be along soon enough to sort your issues.

    ;)
     
  34. johnbryanpeters

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    49ers?
     
  35. Sandwich

    Sandwich just shake your rump
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    what we really need is a new bottom bracket standard.
     
  36. roflbox

    roflbox Turbo Monkey

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    handle bar diameter
     
  37. Sandwich

    Sandwich just shake your rump
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    Pedal thread diameter
     
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  38. roflbox

    roflbox Turbo Monkey

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    proprietary fasteners, and new thread pitch standards on screws.
     
  39. johnbryanpeters

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    Yes, let's go to British Standard Whitworth.
    .
     
  40. Sandwich

    Sandwich just shake your rump
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    Torx? Let's just round it out and make everybody use ez-outs to loosen anything.
     
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