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Can't get wheelbase, front centre and front end correct


I'm trying to model a Ribble CGR AL size S for a client, to see if he should choose a S or M

I've entered all the data I can find online about the bike from Ribble and geometry geeks. I can't get the wheelbase to match up. Where am I going wrong?



Ribble CGR AL size S specs

I just worked out the following model based on specs from the Ribble web site:

I posted the model to the design archive at: bikecad.ca/1706335826399.

Most of the dimensions in the geometry chart can be directly input. However, with top tube length, stack and reach and front center and head tube length, you have to choose which to make driving dimensions and which you'll leave to be driven. I chose to enter front center and head tube length. Initially, the stack and reach didn't match with the specs. However, the specs don't list a dimension for fork length. I therefore lengthened the fork until the stack, reach and top tube length all matched with the published specs. Another dimension I couldn't find a value for was lower stack height. However, I used 1mm for that since it appears that this bike uses an integrated headset.

Another trick I employed when matching up the stack and reach was setting front center to 605.4mm. If I used 605mm, the reach was off by a millimeter. However, by using 605.4mm for front center, that boosted the reach by the extra millimeter needed, but 605.4mm still rounds down to 605mm to perfectly match the published specs.

The specs don't list wheelbase but this is simply a function of chainstay length, front center and BB drop. So if we trust those three dimensions, the wheelbase has to be as shown above. Out of curiosity, I checked what was listed on Geometry Geeks which appears to have various entries for this bike. I noticed one with a wheelbase listed as 1023mm which is mathematically impossible, so should be disregarded.

Brilliant, thank you so much!

Brilliant, thank you so much!

I'm glad to hear your comment about the wheelbase. Wasn't just be me being a total noob

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