I'm getting a rush and I have been trying to figure out what the perfect size is for me. I was wondering if any of you who have experience with the frame can give me some advice. I'd either get the 55 or 57, the 55 has a 55 top tube and the 57 has a 56 top tube. (the 55 and 57 is measured c-t for the seat tube). I have ridden a 55 with a 100mm stem and it felt ok, possibly a little small, but The thing is I'm also used to ridding a bike that is to big for me, so me conception of what is small might be off... I'm not sure.

I'm a hair under 6ft and have about a 34inch inseam. I'm leaning towards the 57 with a smaller stem, but was wondering if I would be better off with a smaller frame or not. I know I'm nitpicking but any advice would be greatly appreciated.

here's the geometry:

https://www.somafab.com/geometry03.html

I'm about 5'10" with a 34" true inseam (crotch to floor with riding shoes on) and I ride a 55cm with a 100mm stem.

It fits me really well, but that doesn't really tell you anything.

i'd say go for the 57 no doubt. that is what i am riding now (pista) and it fits me very well. in general i think you would rather have something a touch too big than too small because i think it is easier to compensate for a larger frame than a smaller one. no?

Choose the frame based on your top tube measurement. I think the measurement is from navel to chin. Or you can use one of the many fit calculators on the web.

The Rush has a huge standover, so if anything, I'd go a bit smaller than normal.

I'm just under 5'10" and I ride the 55cm Rush. They are measured from center of bottom bracket to the top of the seat post collar, is if anything, go a little bit bigger than usual. I could probably ride the 57 comfortably.

thanks for the info. If you 5' 10'' guys feel perfect on a 55 the 57 should be good for me. I think i'll go with a 90mm stem though to tighten it up a touch.

Looking at the chart, the 57 has a 1cm longer top tube, so the difference is more in the height. I'd size it based on how you want to set it up -- what bars are you planning on using, and how much seat to bar drop do you want? I'd go 55 if you want to do deep drops or bullhorns, and 57 for a more standard setup or a riser bike. 57 for sure if you have long arms (ape index over 1.5 or so). It's not a huge difference either way, 1cm at the TT is not much and at your measurements the standover doesn't matter much between the two sizes.

I wouldn't even buy a stem until you choose your bars, and then I would find a shop that has a good stem return policy.

i planning on going with bullhorns, nitto RB-018s. I may put drops on it at some point. When i road the 55 I had the seat kinda high.

Did you ride the 55 with bullhorns? Most horns add a lot of reach.

i road it with bullhorns similar in style to the nitto rb-021. just a different brand. So it had a bit more of a dip down to it than the owns I sould get. When i stretched all the way out on them it felt good, but when i had my hands on the elbows closer to me, which is where i ride most of the time in the city, it felt a little tight, at least to what I'm used to. (but again the frame I'm riding is way to big for me).