I cannot emphasize enough the importance of a good fit on your bike. Every time someone tells me something like, "I love biking, but my [.....] hurts if I do it for a long time," I tell them there is probably something wrong with the fit. If you're serious about biking, you need to make sure that your rig is properly fitted to your body, mainly for two reasons: comfort and efficiency. If you think this blog post will teach you how to perfectly fit yourself to the bike, you're wrong. Neither I, nor any other blogger, writer, biker or coach will be able to write anything you can use yourself because you need to be properly trained as a bike fitter and it's often not a one man job (I mean it is, if the man doing the job is not the one on the bike being fitted).
What I will do in this blog is tell you how to estimate your fit and get things just about right. An important skill to know in many situations, but before I get to that, this seems like an appropriate moment for a plug. If you're considering getting a fit done, get in touch with my friend Andrew Weber. Not only is he an expert in making sure you and your bike have a symbiotic relationship, but after he's done, you will probably feel more comfortable on your bike than you ever have before. I certainly did. But for those of you who need more empirical data to get the point, consider this: I got my fit sometime between April 1 and April 13 (closer to April 13th) of this year. Here's my ride from April 1, and here's my ride from April 13. Compare my times on the Hawk Hill segment - the first day out on the bike after the fit, I dropped 24 seconds off my previous best time on a 1.1-mile climb. If you think I wasn't working hard enough on the prior one, just look at my average heart rates.
Well, enough about that, now it's time for the main event of this program. There are many situations in which you'll need to adjust your bike, or a bike, and most of you probably don't have a personal fitter with you at all times. Some of those situations include: shopping for a new bike for yourself or a friend who knows nothing about bikes, adjusting your bike on the road, adjusting a stationary bike at your local spin class and recognizing when things need to be adjusted. Below are some rules of thumb I follow.
When sizing up the bike, standover height is very important, as that will determine what size bike you need and is probably the one thing that is not adjustable. To figure out your size (perhaps in a model you've never ridden), stand over the bike with the saddle poking you in the back. There should be about and inch to two of space between the top tube (the one that runs from the seat post to the handlebars) and your crotch. Now you've got your frame size down. Note: make sure the tires are inflated, as on deflated tires, the bike is about .5 inch lower and even more so if we're talking about a CX bike. And if we are talking about a CX bike, there should be 2 to 3 inches of space between the top tube and your crotch.
Let's say you want to take this new bike out for a quick test ride, and you want the saddle at the correct height. If the bike is on a trainer, that makes it easier, but if it's not, no biggie. Put the bike next to something about your shoulder height, or a wall. Grab the front brake with your left hand (assuming you have a standard setup) and mount the bike holding on to whatever it is that's about level with your shoulder. Put the heal of the shoe in which you'll be riding your bike on the pedal - your knee should be hyperextended. Once you get the saddle high enough that it is hyperextended, your leg should be at the proper angle once you clip in or start pedaling with the front part of your foot as you would normally.
So let's say you took this bike out for a ride and most things feel good, but you're feeling a bit stretched out, as if you're reaching too far forward and you want to check if the bike is maybe too "long" for you. Or you might be feeling to cramped or clustered on the bike. Put the tip of your elbow to the tip of the saddle and extend your arm toward the handle bars, over the top tube. With your elbow touching the saddle and your fingers fully extended, they should be an inch to an inch and a half away from your handle bars. If the distance is greater, you're probably too stretched out on the bike; if it's shorter, you're probably too cramped. There are two easy ways to fix that: move your seat forward/back and/or get a shorter/longer stem. If you choose to move your seat, read below.
If you move the seat, keep in mind that the position of your knee over the pedals will change. Depending on your size and riding style, you want your knee slightly behind or directly over the pedal when your foot is at 3 o'clock. Having your knee in front of the pedal may cause knee problems if you ride this way constantly. To check this, you either need to be on a trainer, or have a buddy holding your bike. Get on the bike and don't touch the handle bars. You should be seated completely upright. Now pedal backwards until your feet are at 3 and 9 o'clock and tilt your head down ever so slightly to look over the knee of the leg that's at 3 o'clock. If you can't see your toes, you're too far forward. You should just be able to get a glimpse of an inch of your foot. This particular adjustment should be dialed in by a professional, but following this advice will get you about 90% there in most cases.
Lastly, the height of the handle bars. On this one, the ball is in your court. If you're an aggressive racer/sprinter, you may want your bars a bit lower. On the other hand, if you prefer the long haul, a more upright position might be easier to tolerate for many hours on the saddle. Just remember that the height of your bars is limited by the length of the steerer tube of your fork and the angle of your stem - so there's only so far you can go before you have to swap equipment.
This is all you really need to know to get is almost right. To get it completely right, contact a professional. It's kind of like the difference between brushing/flossing your teeth and filling a cavity.
P.S. Check in tomorrow, I will have a very interesting blog post that you cycling enthusiasts will surely appreciate.