|
According to this cyclist, the most important number when trying to find a bike that fits is the frame size,
roughly the length
of the seat tube. I have always considered the frame size
to be the distance
from the center of the crank (or bottom bracket) to the top of the top tube (men’s
frames) as measured along the seat tube. This is close to the distance between
your butt and your feet when you are riding the bike. But do not think that
you need a frame that is the same size as your inseam. You have to factor
in the seat and some seat post that will protrude from the top of the seat tube.
You also have to remember that your feet will travel below bottom bracket as you
pedal.
Be careful when comparing frame sizes among different brands. The length of the seat tube (the frame tube that has the
seat at the top of it) is most commonly given when talking about the size of the frame. But this is an imprecise measurement because there is quite a bit of disagreement as to where the seat tube begins and ends. Does it start at the top, bottom, or center of the bottom bracket? Do you measure until you get to the top tube or all the way to the end of the frame? Manufacturers disagree.
If you are trying to size your bike by frame size, you must know how the bike has been measured in order to compare different frames.
A quick shortcut to sizing is the
standover height. The standover height is
the distance from the ground to the top of the top-tube (the horizontal bar on a men’s bicycle frame). Stand over the bike and straddle the top tube. With your feet flat on the ground, there should be a couple inches of clearance between the top tube and your…um…sensitive parts.
In other words, the standover height should be a little shorter than your inseam.
You have to estimate the location of the top tube when sizing a women’s frame.
Having said that, there are a lot of ways to measure a bike and this is just a guideline. The most important aspect to sizing a bike is comfort. Get on the bike. Ride it. Ride it a lot. Take it for several miles. Obviously this is not always an option when looking to purchase a new bicycle, but do what you can. When you pedal, your knee should extend almost completely. You don’t actually want to straighten out your leg all the way, as this will quickly go from uncomfortable to down right painful during a moderate ride.
Once you have decided how tall your bicycle should be, your next consideration should be top tube and stem extension (basically the distance from seat to handlebars). Every body is different, so it is import to let comfort dictate the sizing that you choose. Again, riding the bike a good distance, 15 or 20 minutes at least, will give you the best sense, but if your bike shop won’t allow you to commandeer one of their bikes without supervision, this can be difficult. Furthermore, many riders prefer different extensions for a mountain bike vs. a road bike.
Okay, so you’ve already got a bike and you’re
thinking you need a new one because the old one that you acquired from a friend just isn’t your size. Not so fast you thrifty devil, you. You’ve still got some options here too. I’m assuming that you know how to adjust the seat height. The seat post moves up and down inside the seat tube to give you some height variability. Do NOT pull the seat post out as far as you can.
If you don’t leave enough post inside the tube, the seat could come loose during riding and…well, that would not be good.
Did you also know that you can usually move the saddle forward and backward a couple of inches as well? This can make a big difference. Loosen the nuts or clamps that hold the saddle rails to the seat post. The seat should be free to slide forward or backward.
Do so as you see fit. But be careful to return the seat to a level position when tightening the nuts again.
For the extra serious, you can install longer or shorter stems for the handlebars. These can raise or lower the handlebars, but they can also give you more or less distance between the handlebars and the saddle. You can also get longer or shorter cranks, but this is less of a frame sizing issue, and more important when considering the length of your legs.
Geometry is another factor that serious riders will want to consider. The angles within the triangles of the frame impact the lengths and distances from piece to part.
A frame that is only a bit too small or too big can be corrected with some minor adjustments. For larger discrepancies stem adaptors or special seat posts might do the job. But if the bike is ridiculously big or small, forget it. Sell the old one and get a new one. No amount of tinkering will ever make it a practical ride. You will never enjoy the bike and you will hardly use it, so what’s the point?
|