ccweiss on How to Determine the Correct Frame Size for a Bike

I’d never even waste a second on reading measurements or pulling out a tape measure to measure my anatomy. Maybe that works for some, but I think it’s pretty unnecessary.

 

The only way to measure, in my opinion, is to go to the shop and get a feel for the bike. You’re going to do this anyway, so just skip all the math and head there immediately. Like the shoe, regardless of how much math you have to justify your choice in frame size, it doesn’t mean a whole lot if you’re hunched over or crouched uncomfortably. Fit is all about comfort and comfort isn’t derived from a number. An aching back and sore legs don’t really care much about math. Plus with the amount of adjustability on most bikes today you’d have to be a complete absentee to purchase a bike that’s so wrongly sized it’s unrideable. This is how I’ve always approached buying a new bike and I can’t think of any problems that it’s caused.

My most recent purchase came just a few years ago. I had just moved out to Colorado and getting back into mountain biking for the first time in about five years. I noticed my old bike was in such bad condition that it would cost too much to make it worth repairing. It was also too small. This made reference quite easy. The bike was a 17-inch frame, so I figured I’d want to step it up to an 18 or 19 (all that without resorting to a single piece of measuring tape).

 

I went to a local bike shop and began scouting some bikes that I liked. I pulled them out and straddled the top tube. I like to have a few inches for the boys to clear, so I made sure that I wasn’t cutting it too close. It turned out that the 18-inch frame was just right leaving about 3 or 4 inches between the crotch and the tube.

 

With basic frame sizing out of the way, I focused on what was really important: the overall comfort, positioning and ride of the bike, not to mention components, design and all those other factors. I tried out a few bikes for comparison, adjusting the seat post and saddle position to provide the optimal position: knees bent ever-so-slightly when the pedals are all the way down, elbows bent equally slightly when holding the handle bars and a slight forward lean. Then I took the bike out for a ride to make sure it was comfortable to ride. I hopped off the saddle occasionally to make sure I could easily get a foot on the ground when needed without bonking the valuables. It was quickly clear if the bike size was correct for me.

 

The length of the top tube and stem are the most important measurements in my opinion, which is another factor that makes getting a numerical measurement (down tube) not very helpful. If you look at just how long seat posts are, it’s easy to adjust your seated height, but there’s not as much adjustment to the length of the frame. You can adjust the seat forward or backward to help a little, but it won’t necessarily make the bike more comfortable. When shopping for a new bike this is the main factor size factor I considered.  

While, I prefer a bike with a good forward lean that allows me to get a little additional weight on the front end, I ended up going in an opposite direction. I purchased a Kona, which had a more relaxed, upright positioning to it. While the position was slightly off for my preferences, it was difficult to pass up as the bike itself was the best overall buy in the price range. I adjusted the seat to compensate for the short length and this has been adequate to serve a comfortable ride.

 

I’ve been riding the bike for nearly two years and have taken it on many rides in the mountains and desert and it has served me well. The size has been perfect despite not verifying it with my calculator and the ride has been top notch. The only thing that has taken away from my biking experience is my own out-of-shape condition and my east-coast lungs meeting Rocky Mountain altitude. However, the size has been spot on.