alfu

I am planning on going out to a couple yard sales tomorrow and if by chance I find any decent bicycles worth picking up, how might I measure the frame to determine the right size for me? Should I just bring a measureing tape with me? I'm currently riding an old 57cm schwinn premis.

thanks for any help you can offer.

Scooper

Sheldon Brown has an article on bike sizes HERE. Take a tape measure with you. I hope you mean 57 cm.

John Z

Lots of verbage here, but no directions for fitting a bike.

DMF 

You mean how to find out what size you should be riding?

a) Professional fitting system ($),
b) test ride various sizes and geometries until you find out what you like,
c) wind tunnel testing ($$$$).

Even then, there are different ways to achieve that fit on a specific bike. A top tube length (IMO the more important measurement) implies a certain reach, but the reach can be modified by both stem length and saddle position.

Scooper

My bad. I thought the OP was asking about how to measure the size of a bike (thread title).

For a traditional geometry road bike, the attached chart might be helpful as a starting point.

DMF 

It might help to specify how leg length is measured for purposes of that chart. I believe that it's hip bone to floor, not inseam.

Scooper

The "inseam" (or rider leg length) for the purpose of the chart is from snugly into the crotch to the floor standing in stocking feet with feet spread about a foot apart. The easiest way to measure is to stand back against a wall, feet spread about a foot apart, and tuck a large format book snugly into your crotch on one edge and against the wall on a perpendicular edge, then use a tape measure to measure from the top edge of the book to the floor.

DMF 

IMO the chart reads too large. E.g. I'm 6'2" leg 33" and supposedly my 59 is (marginally) too small. But I've tried 61 and 62 and they're just too darn tall for me in a straight (non-compact) geometry. I could easily ride a 58. Of more importance to me was the 57.5 top tube, anyway.

But the chart is a decent starting point, bearing in mind that seat tube length is hardly the only pertinent measure of fit.

urbanknight

If you're yardsale shopping you could just use the tailbone method: If the seat is not extremely low or high and the saddle touches your tailbone while standing over the bike, it will at least come close. My first 2 road bikes were fitted this way and aside from buying a longer stem on one of them, I was able to fit them perfectly.

Scooper

+1

If you've got an average torso to leg length ratio (height/leg length = 2.0 - 2.2) most production bikes built with traditional geometry will come close using the chart attached to my post above. Folks with abnormally long torsos or legs do often have fitting problems with production frames, and can sometimes get a decent fit by adjusting the seat setback and/or changing the stem height and/or extension. If that doesn't work, it usually means getting fitted for a custom frame.