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Old 08-20-09, 10:43 PM   #1
RabidUnicorn
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#CM vs. height??

I come from a BMX background and have recently become more interested in other types of cycling and was looking to purchase a fixed gear, but have had one question: when bikes are listed as 55cm or 57 cm or whatever, I'm assuming they're talking about TT length. What size is best for a 5'9"-5'10" person?

Thanks for your help!
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Old 08-20-09, 11:14 PM   #2
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Actually normally they are referring to seat tube length and there are multiple ways to measure it.

All measurements are from the center of the bottom bracket spindle but the stopping point for the measurement can be the centerline of the top tube, the top of the top tube or the top of the seat tube. Fine in the days of horizontal top tubes but not as relevant now. Differences in bottom bracket height can also cause differences in standover height for bikes which claim to be the same size. One reason why internet buying is dangerous for less than experienced bike riders. Too easy to end up with a bad fit.

Ask around among bike riders to find a good LBS that carries a bike that you like and get fitted as there is too much difference in leg and torso lengths between individuals of the same height to make a size recommendation. Also there are lots of web sites with information available if you do a Google search for "Bike Fitting". Even there you will find conflicting opinions however.
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Old 08-20-09, 11:28 PM   #3
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Ah, I see. I was looking to find something off craigslist so would asking the owner his height or maybe even his inseam give me more insight to the true size of the bike?

Thanks for your help.
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Old 08-21-09, 12:46 AM   #4
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Originally Posted by RabidUnicorn View Post
Ah, I see. I was looking to find something off craigslist so would asking the owner his height or maybe even his inseam give me more insight to the true size of the bike?

Thanks for your help.
I am 5'9" and a 53-54-55 worked for a straight tube road bike. But I have a 29-30" inseam. I think you should go check out some new bikes at a LBS and see what fits you best. But equally important is the top tub length. So go set on a few bikes and get a better idea of what fits. Remember some bikes list their size as Small, Medium, Large and Xlarge.
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Old 08-21-09, 12:59 AM   #5
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Originally Posted by RabidUnicorn View Post
Ah, I see. I was looking to find something off craigslist so would asking the owner his height or maybe even his inseam give me more insight to the true size of the bike?

Thanks for your help.
When I'm looking at bikes on Craigslist I always ask the sellers their height, and try to figure out from the photos how they had the bike adjusted. It's not foolproof but at least helps me figure out whether it's worth my time to go look at a bike.
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Old 09-05-09, 12:59 PM   #6
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Not to bring this back from the dead, but is there a general length that corresponds to a general height? Of course it won't be perfect, but there must be some approximation. What is that?
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Old 09-05-09, 01:44 PM   #7
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I am 5'9" and a 53-54-55 worked for a straight tube road bike. But I have a 29-30" inseam. I think you should go check out some new bikes at a LBS and see what fits you best. But equally important is the top tub length. So go set on a few bikes and get a better idea of what fits. Remember some bikes list their size as Small, Medium, Large and Xlarge.
This is what you have to beware of--I am 5'6" and I have an inseam of 30"-I ride a 51cm- or a Small or Medium in Compact sizing on road bikes--Or a 15 1/2" on the MTB but I can fit on the front or rear of our offroad Tandem that is a Large/medium.

Frame sizing will give you an indication of the size that may fit you and most go by standover height of the frame. WRONG. The important measurement is top tube length- if you must take one measurement as a rule.

Difficult to know on your first bike as to how it should fit but the main thing is does it feel comfortable? Doesn't have to be exact on your first bike as all it will tell you---Is what your second bike should be on size- type and quality.

Sorry if I am putting you off- but you should try and find someone local to you that rides the type of bike that you are thinking of buying to advise you. It could save a few problems and a bit of money.
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