Your precise bike frame size needs will depend on your height. Regardless, the right size for you is one on which you can sit atop the saddle with your feet flat on the ground. It would help if you also didn’t have to stretch out your arms to reach the handlebars. If you can meet these basic requirements, then the bike is the right size for you.
If you’ve had a problem finding the right size mountain bike, then I think I can help. I’ve put together a few resources that helped me solve this problem. Now they can help you get the best-fit mountain bike for yourself.
Choosing the Right Size Mountain Bike
A mountain bike frame is smaller than that of a road bike. The smaller frame makes it more agile and able to negotiate the varied and tricky off-road terrain that riders inevitably face. You’ll also place your arms more widely apart and sit more upright. Choosing the right size is essential.
As I discovered, the first tool you need to use in your search is a size chart. These charts give you a general idea of what size frame you need according to your height. It might look something like this:
Frame Size (inches)
4’10” to 5’2”
5’3” to 5’6”
5’7” to 5’10”
5’11” to 6’1”
6’2” to 6’4”
6’5” to 6’6”
Choosing a frame size is one thing, but you’ll still have to position the saddle and align it with the handlebars. Usually, the saddle should be in line with the handlebars, but it can also be placed slightly below them if that’s more comfortable for you.
When you’ve positioned the saddle exactly where you want it, you should sit in the seat to try it out. As you’re sitting in the saddle, both of your feet should reach the ground. The balls of your feet should also be touching the ground.
Next, you should have enough flexibility in reach that you can sit comfortably upright or leaning forward to whichever degree you need while riding. Your arms should be slightly bent as you hold the handlebars, and you need the flexibility to move in support of your upper body as you fly through those mountain trails.
A bigger frame puts greater demand on your arm and leg reach. If you’re in the middle of the ranges above, then the recommended frame size is likely to be ideal. If you are at the borderline heights, then you might be better on a frame one size up or down. This is where trying bikes for size comes in. It’s important to sit on a bike with the saddle set to the right position and see how it feels.
There are pros and cons to getting a frame size, either one size too big or small for your height. Getting a larger frame gives you a longer wheelbase, which is great for traversing tricky rock obstacles. On the other hand, it also means the bike is a bit less nimble for fast mountain trail riding.
Conversely, a smaller frame gives you shorter reach, which allows you to sit more comfortably upright. It will also handle more nimbly but be less effective clambering over tough obstacles in your way.
How to Measure a Mountain Bike Size?
The key measurement for the bike’s size is how big the frame is in inches. This can be determined by measuring the length of the seat tube. First, you have to locate the top of the seat tube. In the diagram below, the tube is the part highlighted as red.
At the bottom of the frame, the lower end of the seat tube joins where the two crank arms come together. The frame size is the difference between point C and T mentioned, with C representing the center of the bottom and T showing the seat tube top. Now you have your frame size.
What Mountain Bike Wheel Size is Right for Me?
There are three main wheel sizes that you’ll find in the mountain bike market. They are as follows:
- 26” – used for dirt jumping, freeriding, and also kids’ bikes
- 27.5” – also known as 650b
- 29” – also known as 29ers
The measurements above refer to the diameter of the tire. A second measurement that is paired with the diameter is the tire width, also in inches. The sizes will then be written out as follows:
<diameter> x <width> - 29 x 2.8; 27.5 x 2.4, etc.
The wheel size that is right for you depends on how you’re going to use your mountain bike. From what I’ve found, 29ers are the best for a mountain bike being used for cross country and trail riding that is also more than 17.5” in frame size. Smaller bikes for the same purpose should be fitted with 27.5” wheels.
Wider tires provide greater traction, so the more your traction needs, the bigger that width number should be. The most challenging trails and obstacles will require a tire of about 3 inches in width. More easygoing terrain can handle 2.25.” For a standard mountain trail, anything from 2.25” to 2.4” is acceptable, but anywhere where the bike is undergoing more strain from rocks and possible drops, then 2.5” is the minimum width you should take.
What Size Mountain Bike Frame for Me?
As I mentioned further up, your first step should be to consult a sizing chart. This will put you on the right track to selecting the right frame. It will at least narrow it down to between 2 and 3 choices, especially those who fall on the height borderlines.
Another thing to think about with the frame is its geometry. If you’re a tall rider, for example, you’ll need to check the seat tube's specific length because this determines how high or low you’ll be able to adjust the seating to suit your height. You’ll also need a longer crank. Another key geometric form is the wheelbase created by the frame. A longer wheelbase is better for negotiating rocks and tough obstacles, but a shorter one is more agile for fast turning.
It would be best if you also looked at the seat angle, head angle of the fork’s steerer tube, handlebar height, width in relation to the frame, and more. The right size frame is one in which all of these things can be adjusted to the point where they become comfortable for you during any ride that you’re taking.