bumpalong

Does anyone know of a top tube sizing recommendation chart, similar to the many available to seat tube sizing?

While I am pretty clear on what feels right from seat tube length point of view, I am always questioining what seems to fit best from a top tube perspective. The same bike that some days seems just right, on others seems a little off. I think it depends on what sort of riding I am doing, and how flexible I am on that day, but I often find myself second guessing a prior impression.

I am also toying with the idea of creating a sizing recommendation calculator that combines suggested seat tube, top tube, crank length and bar width. I realize I could be wading into the very muddy waters of 'personal preference', but it may be fun to try. Who knows, with the right algorithmns it might even be able to recommend appropriate color schemes

auchencrow

I think this can only yield a dichotomy of opinions, because (as with seat tube sizing), there are those who ride the drops, and those who ride the tops.

Ex Pres 

I think most of those seat tube sizing charts assume a TT of the same length or maybe a cm shorter, as that was normal geometry for Euro frames back in the day.

Some British and American frames, on the other hand, seem to have a TT that never lengthened beyond some arbitrary number. You'll see a 23" and a 25" frame, both wiith the same 22 1/2" TT. Or maybe it's just the ones I've had contact with personally.

And bar width would be offset by shoulder width in your sizing calculator, assuming the rider is using the right width bars, so that's a factor you don't really need.

Crankarm length is similar, but can affect seat setback, therefore the TT & stem length. Oh, now it's just easier to get on the professional fitters contraption at the LBS. That's your issue.

Takeaway from this: The ST chart is good enough for a starting point.

bumpalong

Ok, leaving behind the possibility of a bike fitting 'killing ap' for now, is there a calculation to be used for determining ideal top tube size? Is it some ratio applied to torso length? If so, how is a torso measured anyway?

randyjawa 

I am no expert when it comes to fitting a bicycle to me. That said, I did take the time this summer to properly fit a bike and then I took measurements. My intent was to find a comfortable fit and then record the measured information, hoping to transfer the information to other bicycles. It worked great for me but I do doubt that my finding would be of much use to you, or anyone else.

auchencrow

The only rule of thumb I've ever heard of in this connection is that when riding the hoods, the front axle ought to be in approximately the same line of sight as your bars. - I would think that this would be the product of several ergonomic metrics, as well as both TT length and headtube height, not just your torso length.

In my own experience, achieving that, it would be a fairly large, stretched-out sort of bike.