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  1. #1
    mtbr member
    Reputation: GnarBrahWyo's Avatar
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    Jun 2012

    More travel in fork than rear shock?

    Are bikes ideally supposed to have the same amount of travel up front than in the rear? Would a fork with 15 mm more travel than the rear shock have wonky ride characteristics? Always been curious about this.

  2. #2
    > /dev/null 2&>1
    Reputation: Procter's Avatar
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    Feb 2012
    It depends.

    In summary, yes people routinely run a fork with a little more travel than the rear shock, but, you can't add too much, and check your mfctrs specs to see if a +15mm will void your frame warranty.

    1) How does fork travel affect bike handling? As the fork travel increases, this makes the head tube angle more slack, giving more stable steering at speed, but the steering will feel slower during climbing and make the bike feel less nimble on technical climbs. This also slightly raises the bottom bracket giving you more clearance but also causing you to ride higher which feels less stable, but ... you you probably won't notice too much for a 15mm increase.

    2) Are bikes supposed to have more fork travel than rear travel?

    It depends: When a frame is designed, the designers plan for a fork of a specific height, for a specific head tube angle. Usually a frame has a recommended fork travel, or a range. The upper limit is there for two reasons:
    First the mfctr is trying to keep the geometry (primarily head tube angle) within some expected range so that the bike handles as expected. But, riders know the tradeoffs between travel and handling and may decide to increase travel at the expense of steering response.
    Secondly (more importantly) longer forks put more stress on the head tube junction and can break the frame - if you imagine a bike with a looooooong fork (like one of those chopper motorcycles) you can picture all the additional leverage that this puts on the head tube, causing more stress during jumps/drops/normal riding and potentially breaking the frame. So, check your frame specs, and if you go over the recommended fork travel, you do so at your own risk.

    For example my Yeti ASR5c has a recommended fork 140mm-120mm for 140mm rear travel (the fork max = the rear travel). In their geometry specs, they specify that the head tube angle will be 67.0 with a 140mm fork, and 68.0 with a 120mm fork. This bike is intended to be a light trail bike, hence they did not go out of their way to beef up the head tube area to support higher travel forks.

    On my All Mountain Firebird on the other hand (167mm rear travel) the recommended fork is 180mm - 160mm. So in this case the frame allows a fork with +13mm more fork travel than rear travel. This is typical of an all mountain bike where riders routinely want more travel and actually prefer a slacker head angle for more stable handing at speed. The weight tradeoff (for reinforced head tube junction) is acceptable as the frame is a beefy all mountain frame.

  3. #3
    mtbr member
    Reputation: GnarBrahWyo's Avatar
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    Jun 2012
    Yeah, I am thinking of running a 140 mm fork and a 125 mm rear shock. Nothing crazy, just wondering how it might change the behavior of the bike. Thanks for the write up.

  4. #4
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    Reputation: GnarBrahWyo's Avatar
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    Jun 2012
    I think I should be okay with only 15 mm.

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