Mountain Bike Frame Size: How to Know if it Fits you Properly
One of the most important things to consider is the mountain bike frame size. The size of the mountain bike frame and how well it fits you are determined by many factors, including the length of the seat tube and the length of the top tube.
A Seat Tube
B Top Tube
C Effective Top Tube Length
D Standover Height
E Head Tube
The bicycle seat tube (A) is the tube that goes from the seat post to the bottom bracket. The length of the seat tube determines the mountain bike frame size. Some manufacturers provide bike sizes in inches, while others use small, medium, large, and extra large.
The seat tube also helps determine your bicycle standover height (D), which is the amount of space you have between the top tube and your crotch when you are standing over the mountain bike with the seat poking into your lower back. If you are trying out a mountain bike in a store, you can determine its standover height by straddling the bicycle, lifting it straight up, and measuring the distance between the wheels and the floor.
For cross country mountain bikes, you want 2 to 4 inches of standover height, or even more if you plan to ride aggressively. For downhill and freeride mountain bikes, you want 6 to 8 inches of standover height.
When sizing a mountain bike, the top tube length (B) is also important. The top tube runs from the head tube to the seat tube, which determines the distance between your seat and handlebars. The distance should allow you to ride comfortably with just a slight bend in your elbows as you grip the handlebars.
If you are buying a mountain bike frame online, be aware that manufacturers measure mountain bike frame size in different ways. For example, sometimes the seat tube is measured from the middle of the bottom bracket to the middle of the top tube and sometimes it is measured from the middle of the bottom bracket to the top of the seat tube. Because of this, a size 18 mountain bike from one manufacturer may not be the same as a size 18 from another manufacturer.
Often, manufacturers that sell mountain bike frames online provide information on how the bike is measured, as well as fitting charts. Some also provide measurements of standover height, so if you know your inseam length (which is the length from your crotch to floor) it is easy to determine if the height of the frame will work for you.
Another thing to be aware of when looking at mountain bike frames online is that the angle of the top tube affects the distance from the saddle to the handlebars, so this measurement is not consistent from one bike to another. Rather than using the measurement of the top tube, the effective top tube length (C) can be used, which is the horizontal distance from the center of the head tube (E) to the center of the seat post (A). This is a more reliable measurement Since it can be compared from bike to bike and it is often provided by online manufacturers.
Your mountain bike seat, handlebars, and shocks should also be adjusted to fine tune how well your bicycle fits you. For more information on how to make these adjustments, please visit our page on Mountain Bike Fit
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