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I want to introduce myself to the cyclocross world, I'm looking for my first bicycle. I found a great used bike with a frame at size 54 (54 seat tube x 54,5 top tube), which would be slightly small for me(1.86 m tall). On my road bike I use a frame in size 56 (54 seat tube x 56,5 top tube) with a 130mm stem, it has the perfect fit.

In my research I saw that cyclocross bikes need to be 1cm to 2cm shorter in full reach, which would allow me to continue using a 130mm stem, but would using such a long stem in a smaller frame affect the handling of cyclocross specificities(bunny hops, short and steep climbs/descends, 180º turns)?

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  • Will you get your arm & shoulder through the front triangle? I find it a close thing on my 56 cm frame that fits me with a 13 cm stem.
    – gschenk
    Commented Jan 25, 2019 at 19:32

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Couple of problems I can think of:

Reduced front-center (BB to front axle) on the smaller frame which means more toe overlap.

For the same reason the front wheel will be tucked further under your center of mass, which may create problems on steep descents.

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  • "For the same reason the front wheel will be tucked further under your center of mass, which may create problems on steep descents." Not necessarily, since one would slacken the geometry by moving the seat further aft to keep the centre of mass (COM) over the bottom bracket. However, since the mass is distributed over a larger area and farther away from the ground the COM would shift much farther forward at descents then for a smaller rider. In simpler terms, the torque require to turn you about the front axle may be smaller on a larger frame with shorter stem.
    – gschenk
    Commented Jan 25, 2019 at 22:05
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    @gschenk It'a a bad idea to move the seat to resolve reach issues as you are then creating fit issues for the lower body.
    – Argenti Apparatus
    Commented Jan 25, 2019 at 22:11
  • its not moving the seat to solve reach issues, its to keep the COM over the bottom braket on level ground. In order to avoid fit issues of the lower body. The longer exposed seat post length might take care of moving the seat back already in a CX bike since seat angle is usually so slack (eg 73.5).
    – gschenk
    Commented Jan 25, 2019 at 22:19
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Let's have a look at geometry of example bikes.

For the Ridley X-Night a pure CX race bike, the difference in reach* between a size 54 and a size 56 frame is only 9 mm. That may very well be significant for handling of this bike, if the geometry of this pro race bike is close to the edge of required stability.

The aluminium Focus Mares is built for a different market segment, that includes CX beginners as well as commuters. It is one of the more stable CX bikes. The difference of reach for this bike between a 56 and a 58 frame is only 5 mm.

For a more relaxed bike it might not be as relevant if you ship a 120 mm or a 130 mm stem. Both are rather long. Since you appear to be a beginner, you may have to find out if it works the hard way, by trial.

*Reach is the difference in distance from the bottom bracket to the point where steering axle and top tube intersect.

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  • This doesn't address the question of the immediate influence of a long stem on steering. However it may be useful for the specific case since stem lengths will not differ all that much between similarly sized frames.
    – gschenk
    Commented Jan 26, 2019 at 1:59

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