Flexibility of modern bike sizing - what to adjust?


Retro Guru
Hi guys,

I'm having some difficulties adapting to modern bike geometries.
The few I tested felt "longer" than my Peugeot, even though the top tube was actually shorter and the situation is made more difficult by the fact that shops such Evans cycle don't stock the bikes I like, so it's really hard to find bikes to test ride and I need to base myself on numbers alone.

I'm short, at 5'6', so the pool of second hand bikes I can access to is somewhat limited. My Peugeot is a 57cm, but it's way too big for me.
I tried a Genesis Equilibrium size S and it felt OK-ish, so that's the kind of size I'm looking for. But sometimes a Medium sized frame is "only" 20-30mm longer than an S.
How much can I expect to tailor the bike to my liking acting on seat position (fore and aft) and stem length? I see that most road bikes come with very long stems, but I guess that by shortening it too much it would get too responsive and lose in stability.



Senior Retro Guru

your most important and primary measurement should be top tube (or virtual top tube) length. You may be able to fit different stems to get the "correct" length - certainly in terms of reach, but each TT length/stem combo will produce different results in terms of bike handling and therefore descending/cornering attributes.

I am told that TT length is what the pros are concerned with.

Unfortunately, the public buy bikes on seat tube length cos we like the aesthetics associated with lots of seatpin out and slammed stems.

From your current stable of bikes, try out your different bikes, see which handles best and go with something similar top-tube wise. If that means less seatpin out, so be it

…. my tuppence anyway, others may say different ...


Retro Guru
I am lucky in the sense I don't pay any attention to the aesthetics of the bike, surely not to the aesthetics of the seatpost!
I only got to know today as I was searching info that for some reason most riders seem to like long seatposts...
With all the good looking features in a bike, why this one, it baffles me.

Anyway yes, seat tube length is almost meaningless, I see widely different bikes, size wise, that have the same top tube length. I guess I would need to try more bikes, and for a longer period of time, to get some experience in what I actually like in terms of geometry.
Maybe as first modern road bike I should get something "random" (i.e. chosen as educated guess), and then find the perfect fit later on.

I'll nip in Evans Cycle tonight to fee what a size 51 Cannondale (top tube should be roughly 53cm) feels like.


Senior Retro Guru
Worth keeping an eye out with your local LBS to see if they do "try days". Mine's just done an Orange one for example.

I sympathise it can be hard - sometime "initial feel" changes after an hour on the back of slamming some single track/DH (or whatever) - some times it doesn't go away.

Any mates close to your size?