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A Question For Cyclists...

S

ShotgunSteven

Lifer
I know how to determine what size recurve bow and what size cross-country skis a person should use, but I was wondering if there was a formula for determining what size of bicycle frame one should ride. I am either getting a mountain bike or a mountain/street hybrid. I may buy new, or I may buy one of the two that a co-worker is selling.

Other than just sitting on the thing and seeing if my feet reach the ground, what should I check?

UPDATE: Bought the Bridgestone bicycle she was selling. I liked it better than the Specialized Hard Rock she had. It fit me better, and is just more comfortable to ride. I might spring for a new bike later, but the $35.00 price tag was hard to pass up. 🙂 Thanks for the help, folks.
 
Originally posted by: ShotgunSteven
I know how to determine what size recurve bow and what size cross-country skis a person should use, but I was wondering if there was a formula for determining what size of bicycle frame one should ride. I am either getting a mountain bike or a mountain/street hybrid. I may buy new, or I may buy one of the two that a co-worker is selling.

Other than just sitting on the thing and seeing if my feet reach the ground, what should I check?
Click to expand...

the seat is adjustable, the frame ain't.

when sitting on it your legs should fully extend while pedaling, so you shouldn't be able to sit on the seat and touch the ground with both feet. If your legs aren't fully extending it's bad for your knees and it makes your thighs ache.

a basic guideline for frame sizing is to stand over the bike's top tube. if there's an inch between the tube and your crotch it's probably the right size.

http://www.cyclemetrics.com/Pages/Docs/6-BikeFitting/Sizing/sizing.htm

also check out mtbr.com for more info.

what kind of bikes is your co-worker selling and for how much? make sure they fit you
 
I thought your knee was supposed to be just slighly bent at full extension?
 
Originally posted by: DrPizza
I thought your knee was supposed to be just slighly bent at full extension?
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QFT.

I'd go for a smaller frame size if possibleas it'll be lighter. Just get a longer seat post so you can adjust the saddle to the optimal height. Also, check the length of the bike so you're not leaning too far forwards.
 
Originally posted by: David Brent
a basic guideline for frame sizing is to stand over the bike's top tube. if there's an inch between the tube and your crotch it's probably the right size.
Click to expand...

That's the basic idea that I was going to post as well. Don't want to hop off the bike and end up crunching yourself....

But I'd take some time and go to a local quality bike shop and have them size a frame for you. Then take that informatino and shop around...
 
Originally posted by: loic2003
Originally posted by: DrPizza
I thought your knee was supposed to be just slighly bent at full extension?
Click to expand...

QFT.

I'd go for a smaller frame size if possibleas it'll be lighter. Just get a longer seat post so you can adjust the saddle to the optimal height. Also, check the length of the bike so you're not leaning too far forwards.
Click to expand...

The difference in weight between the sizes of frames isn't that significant of a difference. I used to have a frame that allowed me to go far far faster than any bike I've had in the past few years.... I wish I still had that frame - it worked just right for my body. I'd consider replacing my current frame with one just slightly longer, but it's not really worth the time and money to me to do so. But, I've got to change the gears on it... I can climb anything steep with it, but the gears limit my downhill speed to coasting... my legs can't possibly pedal any faster... I'm limiting out around 45-50 mph (pedalling). Maybe it's safer that way though 🙂
 
Have someone hold the bike upright for you.

Stand on the top tube of the bike, then allow yourself to drop down while straddling the top tube.

If you can still have children, the bike is the right size.

For you, I suggest starting with the largest frame and working your way down.
 
top tube clearance is a terrible rule of thumb to size a bike... because some are now built with a slanted top tube or in compact geometry with greater slant... what is important is top tube (or "virtual" top tube length)... i can give you a rough bike size to start given your height... you want your back to be at (roughly) 45 degrees and work from there...

most importantly is the ride ... once you work out the small details (seat post height, stem length, stem ride, handlebar width) go for a long (20 mike) ride and see how comfortable you are on the bike
 
Originally posted by: Amused
Have someone hold the bike upright for you.

Stand on the top tube of the bike, then allow yourself to drop down while straddling the top tube.

If you can still have children, the bike is the right size.

For you, I suggest starting with the largest frame and working your way down.
Click to expand...


Despite the fact that you swear by this method after testing it thoroughly yourself, I will refrain. I am not an expert in the field like you. 😛
 
I have nearly 3" of clearance on my mountain bike (extra-long 400mm seatpost), and barely 1" on my road (which is really 1 size too large - too long). I would recommend more clearance, as there are no significant disadvantages to a smaller bike that provides adequate reach to the handlebars and distance to the pedals.

Do you trust your coworker to help you properly fit it? I think pretty much anyone would just opt to make the sale if the fit wasn't egregiously wrong. I would buy new from a shop that has helpful staff.
 
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