What Size Bicycle Do I Need - Bike Fit
Good fit defined
A rider pedaling a bicycle touches the bike in three places; pedals, saddle, and handlebars. For the bike to fit properly, these three points must interface with your body in a comfortable and functional way. In other words, if the saddle, pedals (and shoes), and handlebars (plus grips and controls) do not fit your feet, hands and seat, the bike won’t work its best for you.
The three points of contact must be oriented correctly for you to benefit. Properly oriented, your muscles will work at their optimum. No muscles, ligaments, or tendons will be strained. Aerodynamic drag will be at a minimum.
In addition to the relatively simple task of accommodating your body for comfort, the bike should ride better. Your center of mass should be positioned over the bike to accentuate your pedaling power while also balancing you over the wheels for the best bike handling.
Put more simply, good fit results in your feeling completely relaxed on the bike over long periods of time. If your bike fits well, you should not feel like you need to squirm around, nor should you have excess tension in your shoulders, arms, or anywhere else. Basically, you should be comfortable, first and foremost.
How performance effects fit
The higher the performance level of your riding, the greater the forces applied to the bike, and thus to you. Forceful riders press harder on the pedals. They corner harder, and when riding off road their extra speed generates higher forces when they hit bumps. The forces applied to you on the bike are the result of a Newtonian law that states all actions have equal and opposite reactions. When you are riding, higher forces demand better fitting if comfort is to be maintained.
However, in some cases greater forces may be found when your are riding less forcefully. If you are not pressing firmly on the pedals, you’re not lifted by the pedals. As a result, the casual rider often applies their entire body weight to the saddle.
Regardless of the level of your riding, our definition of good fit holds true. Every rider should use the least muscle energy possible to support themselves on the bike, to stabilize themselves on the saddle, and to apply power to the pedals. To be relaxed requires that you be as comfortable as possible.
Fit info in this Tech Manual
On the specifications page for each bike model, we have listed the Fit items for that model, including the lengths, angles, or widths of the handlebar, stem, crank, and seatpost.
In addition to the measurements of the hard parts, we list Rider Height. This dimension is the median height of the average rider who might fit this bike in an average way, with its handlebars at their highest position. That’s a lot of qualifiers, but the information can still be valuable in helping you quickly fit a given model. Some models do not include Rider Height, either because that model offers too much fit adjustment to be defined, or simply because it’s a one-size-fits-all. So here’s all those qualifiers explained.
Median Height- Different bikes offer different ranges of fit. Generally, the more bent over you are, the more noticeable a poor fit. Most bikes fit a range of heights.
Different bikes will have a different range. We have not attempted to define how wide the fit spread is on a given model; the variables are too many. Instead, we have listed the median, or middle. In other words, if we say a bike fits someone 70” tall it may fit someone from 69 to 71”, or possibly (depending on the model) with a wider range from 67 to 73”.
Average rider- When we design or spec a bike, we have a certain style of riding in mind. As an example, when we spec a 8500, we’re expecting that the bike will be either ridden by a racer, or someone who likes to ride like a racer. That doesn’t mean you can’t ride a 8500 on the bike path. But someone buying a 8500 exclusively for bike path riding isn’t riding in an average way for that model, and will likely want to tune the fit to their purposes.
Average Fit- We’ve studied a lot of riders over the years, and we can draw some conclusions about the way a bike fits the average person. But some folks aren’t average. Those with specific preferences, injury, or other abnormalities may require or prefer a nonaverage fit. As examples, consider two people of the same height but different weight. At 6’ tall, a 130 pound person will sit on a bike differently than someone also 6’ tall who weighs 260. Incidentally, neither of these folks would fit our definition of average.
Highest handlebar position- We made these fit estimations with the stem at its highest point. With Ahead stems, that means all the spacers were under the stem. With quill stems, the handlebars reach their maximum height with the stem pulled up to the minimum insertion line. With adjustable stems, it’s calculated with the stem at a 40 degree angle. Lowering the bars, or changing the parts, changes the fit of the bike as well as its Rider Height.