Bicycle Size & Fit

By Jim Foreman

Every custom frame makers had his own system for sizing a bike but I’m going to talk about an off-the-rack bike. Far be it for me to start an argument with any of the frame builders because they know what will make a customer happy. My figures are more general and hopefully will keep someone from buying something that’s totally wrong for them. I’m talking about road touring bikes with a level top tube and people with an average build. There are some people who simply cannot find an off-the-rack bike to fit them.

Just like buying shoes, you have to know what size you wear. To find the proper size bike, you need your inseam measurement. This isn’t your pants size but something you will actually measure. This works a lot easier if you have help. Take your shoes off, stand with your back against a wall and raise a book at least an inch thick firmly against your crotch. Make a mark on the wall at the top of the book. Take 2/3 of that distance and that is the frame size you need. Frames are measured from the center of the crank to the top of the top tube along the line of the seat tube. Some companies measure their frames from the crank spindle to the center of the top tube and others to the top. That’s only half an inch difference and you will be working on your actual inseam length.

When you find a bike your size, stand over the bike and you should have “some” clearance between your crotch and the top tube. By “some” you should be able to lift the handlebars and have at least an inch of clearance between the front tire and the floor. That means at least half an inch between the top tube and your crotch. You can get away with buying a bike an inch smaller than what you need but that’s about all. You should pass on a bike with more or less clearance than that. Trying to make the wrong size bike fit you is a waste of time and effort.

Next comes saddle height. Greg LeMond came out with this figure and it works well enough as a starting point. Multiply your inseam by .883 to get the distance from the center of the crank spindle to the top of the saddle measured along the line of the seat tube. If everything else is right, you should have about 4″ of seatpost exposed.

Go ride the bike for a bit to find the sweet spot where the saddle feels right. You will definitely need help for this one. While sitting on the bike in your comfortable riding position rotate the pedals to where one is pointed straight forward. Have someone drop a line with a weight on it from the bump you can feel just below your kneecap down past the side of your foot. It should pass through the center of the pedal axle. Then check the other leg the same way. If it’s different (which it may well be) split the difference. Move the saddle back or forward till the string drops through the pedal axle.

You need to get these two adjustments set before you start on anything else because everything from here is based on them. Most touring cyclists find that having the handlebar level with the top of the seat to be about the most comfortable. Shops with the racer boy mentality may want you to have the bars well below the saddle but while that might get you down out of the wind, it certainly isn’t conducive to maximum comfort on the long haul. Lay a yardstick or similar straight object along the saddle and by raising or lowering the stem, and/or switching to ones with different angles, one should be able to accomplish this with little effort.

From here on it gets to be more esoteric than a set of numbers. It’s a matter of what feels best to you and you need to ride the bike more than just around the block to find what feels best. The first thing you need to consider is a stem length which will place you in the most comfortable position while riding with your hands on the flat part of the bar. This will give you your most upright riding position.

The next adjustment is for riding on the hoods. This is adjusted in two ways; by the location of the brake levers on the handlebars and where the drops are pointed. If you have a choice when you buy the bike, tell the dealer not to wrap the handlebars until after you have established the location of the brake levers. The accepted location for brake levers on racing bikes is at the very front of the curve but most tourists find them more comfortable well up on the curve. As you move them upward, it both shortens the reach and raises your hand position. You can get additional adjustment by rotating the handlebars in the clamp. The common limits for this adjustment is anywhere between the drops being level and pointing at the rear axle.

It will take some tweaking for a while to get the bike dialed in for the best fit. It would be a good idea to take wrenches on each ride so you could change settings along the way as you feel their need. The important thing is to make only one change at a time so you will know what effect it had. If you change two or more adjustments at the same time, you will never know which one you liked and which one you didn’t.

If you moved something and it made things worse, return it to the original position before making another change. Make very small adjustments because in many cases, only a quarter inch will make a big difference.

Good luck and may your bike fit like an old shoe.