just got my soma rush from the UPS man. the thing is amazing. my only concern is that it may be slightly too small. i checked the geometry on the soma website (https://www.somafab.com/geometry03.html) and it seems as though the difference between the 51 (mine) and the 53 is minimal. is it worth the cost/time to exchange? is the difference between the two minor or is it really going to make a huge difference? if it matters the bike is not built, i just threw some wheels on there for reference.

thanks

Is the top tube too short? If so, try a new stem?

Get the frame that fits!!! I tried making a too small frame work with a larger stem and it rode like poo. The sad thing is you don't notice till you ride the correct size frame in that make and say... DANG!!!

If you think it might be too small, it probably is.

(edit) I just looked at the SOMA site. I would def go with the 53.

I made the mistake of buying my first road bike on the internet and I thought it was (majorly to small). It wasn't until I went out a purchased a bigger frame (and sold the smaller) that I realized what a dolt I am. So maybe if you think you're on too small of a frame, most of the time you are, but sometimes not.

If my first frame was marginally too small (by about a cm) it handled much better than the too-large.

Get the frame that fits (and make sure it is the frame that fits this time). It is a small expense for a bike that you will like better.

it should be noted that this frame is not built up. i am just basing this on throwing a pair of wheels on there and noticing that i dont have the inch to an inch and half between the TT and my crotch. if the difference in top tubes between the 51 and 53 is about 10mm, would this be compensated for by a 110 stem (which i have)? or are there other geometrical figures i should take into account?

I use an 110 stem on my cross bikes, and track bike. I find it a perfect balance.

That isn't a good measure of fit at all. The old "crotch space" measure isn't really critical, in my opinion. Most of my bikes with traditional geometry have less than that. I would be more concerned about reach.

Lemond's formula for sizing the seattube length and thus the frame:

.668 x true measured inseam.

For instance, I have 32.5" legs. (Measured without shoes on, feet 6" apart, floor to crotch using a book as crotch-jammer.)

That translates to (31.5"x.668)=21.71" or size 55.1cm center-to-center seatube. Both my bikes measure 55cm center to center.

As I understand it, TT is a much better measure.

TT correlates with ST. But yes, I agree with you especially with the advent of nasty compact geometry frames.

If you like the way your Panasonic fits you, then try to get as close to that as possible. If you like to change other things like longer toptube or lower standover height, then get a frame that provides this.

Your current frame will be your yardstick.

remember that head tube length changes too, an important factor to consider. it's always better to start with the right size frame.

thanks everybody. i think i will take your advice and exchange for the 53.

Listen to this! Far too many people rely solely on standover, top tube, seat tube and forget head tube. This is the part where saddle to bar drop comes into play. If you want/like a deep drop, go shorter. If not, go larger. I have been down this route, and made the mistake too many times. I cannot deal with more than about 5cm of drop to the top of the bars. (And I hate the look of riser stems). So now I'm building bikes with taller head tubes or going with frames that are one size larger than sales guys in stores would normally 'fit' me to.