Bike sizing/geometry question

Cubic

Hi,

I want to upgrade my frame soon. I've been on the Competitive Cyclist's fit calculator and it recommends:

Seat Tube range of 53.6 - 54.1(c-c) or 55.3 - 55.8(c-t)
Top Tube length of 54.1 - 54.5

I don't know if I'm an unusual shape, but none of the eight or so frames that I'm interested in match those measurements. I tend to be a 54 in one and 56 in the other.

Is there one measurement that is more important than the other?

Is it better to size up or down it this situation? And what is the effect of having a slightly too big or too small frame?

Thanks.

rolf_f

Most frames are much the same proportion so if you are long legged and short bodied, there isn't much choice.

As a started, check the Ribble Gran Fondo and Scott CR1. If they are too short, Orbeas might work as might the Ribble Sportive Racing. If you are after a proper cheap bike in those proportions, you may struggle.

Monty Dog

Reach (toptube) is far more critical than seatpost height as you can simply raise of lower the saddle to suit. Generally, most frame geometry has a longer toptube than seatube or as you get to bigger sizes they are the same i.e. 'square' in terminology. Your other consideration given that you require quite a long seatube is that the frame has a correspondingly long headtube, otherwise you'll be running a huge stack of spacers under the stem which isn't recommended given the load this puts on the fork steerer.

Cubic

Thanks. So it seems like a sportive/relaxed geo bike might be better for me with their longer headtubes?

I think I'll print off a few manufacturers geometry charts and compare headtube lengths for the same top tube. Should help shorten my list I hope.

Cubic

I just measured my current bike and it has a top tube of 56cm and a head tube of 17cm.

If I go down to a 54cm top tube, as recommended by the fit calculator, most bike this size would have a 14/15cm head tube, how would this effect my position on the bike?

Would dropping 2cm on the TT balance out dropping 2cm on the HT or am I likely to feel more or less stretched out?

I'm having trouble visualising it all!

colsoop

Make sure when you measure you are doing so in the same way as the frame you are comparing it too.
But essentially 2 off either measurement willl be the same, also look at the angle of the head tube and the angle of the seat post too as that can alter the feel.

The slightly smaller top tube will allow you more stem options which is good for getting a good fit assuming you aren't over legged or torso'd