Bike size and how to adjust it.

So, I just (sort of) bought a new frame which is 1cm bigger than my current bike. I’m riding a Makino 55cm square with around 7cm of seat post rise, and a 100mm stem. Also, I’m using 170mm crankset. This setup fits me perfectly!

My new frame is a 56cm ST with 55.5cm TT.

My question is, is it going to be a lot difference if I change the crankarm to 160mm and adjust the seatpost rise accordingly? I don’t believe in a very technical inseam measurement etc etc and if according to the inseam measurement, I should be riding a 54cm, but I do feel much more comfortable riding a 55cm ST.

Your views will be much appreciated. And if this topic has been discussed here, please direct me to the thread. I’m actually quite scared of brendan… haha.

don’t change yr cranks.
just lower your seatpost, and if necessary get a shorter stem. problem solved.
unless it turns out that you simply don’t like the feeling of a slightly bigger frame

rightly so. but this is a good question.

take some basic measurements of your current setup eg.

  • pedal spindle (when at 6 o’clock) to top of seat

  • saddle setback over bb

  • front of seat to front of stem

  • assuming your simple swapping parts over replicate these numbers with the new frame (in the above order of importance).

  • ride and see how it feels. make adjustments to suit.

  • i’d be changing seat height before crank length

  • set your leg extension and saddle fore/aft position before you get into stem changes.

another tip Ex-HMC told me was that a good guide for cockpit length is when comfortably seated the top of your bars should appear to cross your front axle. i found this to be very useful for settling on a stem length.


unless, of course, you are devilishly handsome and have unusually long arms…

Brendan is, of course, the exception to the rule, thereby making the rule.
Ex-HMC? Did i die?

no. you’re just no longer metal. don’t you mostly listen to coldplay now? i mean, i’m just assuming, due to your new haircut…

ah good, carry on.

But to actually add to the post, and answer the OP, make sure you do everything incrementally. It will feel wrong at first, even if its ‘right’. Little changes, one or two variables at a time, so if something is wrong, or right, you can pinpoint which change is working for you, and which isn’t.

putting your seat forward or using a non setback post is a major hubbard move so try and adjust stem length instead if you must change the reach

most people tend to ride around on TTs that are too short anyway so you will probably be fine as-is with a few weeks of getting used to it

Yeah I’d thought so. I’d adjust the seat post first before changing the crank if it’s necessary. I don’t think I’ll change the stem tho coz I feel that there’s still room for length adjustment in my current setup. Thanks for the help btw.

I’m just curious if there’s anyone in the forum have any experience in having bikes with different size? I’m not saying 0.5 to 1cm diff but 2cm or more diff. If there is, could you share some insight with us?

p/s I like Coldplay!

Yep, I’ve ridden TTs as short as 55 and as long as 60, seat tubes as short as 49 and as long as 60. I really think you can go fast on anything given enough time to adapt. I started on a 60ST/58TT wheeler with 120mm stem, ran a 140mm stem on my 56TT scapin for many, many years verily happily. then moved n to a 58cm sq (I think) felt with a 120mm stem, a 60cm square lejeune rode very well with a 110mm stem and setback seatpost (the others all had topload posts for the most part). My tourer is 58tt with nearly no seat-bar drop and a 120mm stem. Current roadie is 57TT with 125mm stem and not much drop. I think drop plays a massive part in the whole equation. If youre flexible enough to reach further down, you are more stretched out with the same equipmet… so lowering the bar on a smaller bike will make it “fit” better.

People talk about “my size” and fair enough, there is probably a size that suits you best for certain ride types, but anything within a few cms is fine. Most of us don’t push corners to the limit to realise we need better weight distribution between seat and bars, or are too far on top of the bb… and most younger guys dont mind a big drop for long rides.

I find I ride longer and higher TTs with shorter stems as i get older. I consider it my weakness rather than finding the right size :slight_smile:

And as a footnote, i prefer to ride a bunch of bikes with different positions all the time. I dont think its good for your body to sit in the same position everyday for hours and hours, with the same leg extensions, same shoulder and neck angle. I have three pairs of shoes with different cleat positions, saddle height is different on most bikes, bars are different widths, etc. I’ll never be ultra fast and laser-sharp-skills-dude but couldnt really care less.