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  1. #1
    mtbr member
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    Geometry/Wheelbase

    Hi folks, was just comparing my personal bike with a bike I'll be renting in a few months when I head out west and one thing caught my eye with geometry as it relates to reach, CS length, HTA and Wheelbase.

    Bike 1:
    437mm CS
    445mm Reach
    66.5* HTA
    150mm fork
    1201 Wheelbase

    Bike 2:
    430mm CS
    440mm Reach
    66.5* HTA
    160mm fork
    1176 Wheelbase

    So my confusion is that with a 7mm longer CS, 5mm longer reach, same HTA and shorter fork, how is Bike 1's wheelbase 25mm longer? My guess is that the manufacturers measurements just aren't apples to apples or 100% accurate. Is that most likely the cause or am I missing something further that comes into play? I know it doesn't matter all that much and I'll just get out there and ride the rental...but just caught my curiosity. Thanks!

  2. #2
    since 4/10/2009
    Reputation: Harold's Avatar
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    Dec 2003
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    24,362
    longer fork, 'cause triangles.

    Also relevant, but not included in your numbers, is the height of the head tube plus any potential height of an external lower headset cup because reach is measured from the top of the HT.

    Also fork offset, not included in your numbers

  3. #3
    mtbr member
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    A couple possible factors I can think of:

    Reach is measured to the top of the head tube. So differences in head tube length will muddle the relationship between reach and WB

    Chainstay length is not measured horizontally but at the angle between the BB and rear axle. So the closer the BB height is to the axle height, the more directly changes in chainstay length translate to changes in wheelbase length

  4. #4
    mtbr member
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    Good points above that I didn't think of! The fork offsets and head tube lengths are different between the bikes so I assume that is accounting for much of the difference.

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