You don’t just get a bike you want and ride it. You need to consider many things. And one of the most important is the size of the frame.
You can do this by measuring the frame size. This ensures that it’s the right fit for you. This is also very important because this is where your balancing depends on.
Having the right frame size also makes it easier to maneuver your bike. It also avoids crashing and makes your ride more comfortable.
In this article, we’ll teach you how to measure a mountain bike frame. Remember that it’s all about getting the right size so you can maximize your rides.
Measuring your Top Tube Length
The first thing to do is to first measure your top tube length. Mountain bikes have a top tube that lies horizontally and has a slight slope. This is also called the virtual top tube or effective top tube length.
It’s the horizontal distance from your head tube’s centerline to the seat post’s centerline. The top tube length is also the main factor when naming the frame’s size. They come in different sizes like small, medium, large, and extra large.
Most small frames measure around 50 cm to 60 cm. Meanwhile, large frames measure around 70 to 90 cm. But this depends on the bike brand. Take for example Santa Cruz bicycles which are known for their small sizing. The opposite goes for Nukeproof which has larger sizing.
How to Measure your Seat Tube Length
The seat tube is the tube that runs from your bottom bracket’s center to the start of the seat post. Seat tube length is important because shorter riders need a shorter seat tube. Having a very high seat tube makes pedaling difficult.
Measure starting from the bottom bracket until the uppermost portion of the seat tube. This gives you the total seat tube length. But be careful because most mountain bikes have a kink on their tube. This can alter the measurement and make it inaccurate.
How to Measure Stack and Reach
Measuring the stack and reach depends on frame design because there are multiple linkage systems. Take for example Santa Cruz’s VPP suspension and Trek’s conservative four-bar linkages. You can measure this by getting the length measurement from the bottom bracket to the head tube.
The frame’s reach is where your maneuverability depends on. Having a very high reach makes it harder to shred corners and tackle technical sections.
Meanwhile, having short reach makes your bike more playful. It’s also the preferred choice of dirt jumpers. But this compromises stability on high-speed sections.
The latest bikes with modern geometries have a reach of around 400 mm to 550 mm. Again, this depends on the brand because some manufacture smaller-sized frames than others.
You can align the head tube’s center line with the top edge. Then slowly adjust the level backward and forward until it intersects with the spindle’s center. Measure the distance from the plumb line to the head tube and you have your reach.
How to Measure Your Bike’s Wheelbase
Then there’s the wheelbase which is where your bike’s stability depends on. Longer wheelbases are more stable than the shorter ones. But this compromises the maneuverability because they become harder to turn.
This is especially true on tight corners where your rear wheel would most likely go outside your line choice. Every frame size also has its own wheelbase. The wheelbase measurement is around 1,000 mm to 1,300 mm, depending on the size.
Measure your frame’s wheelbase between the two axles. You can start from the rear wheel axle and go all the way to the fork axle. We also recommend you measure from both sides to ensure accuracy.
How to Measure Your Bike’s Chainstay
The chainstay is the rear-most section of your frame. Frames with short chainstays are more playful than those with longer measurements.
You can easily flick them around and do whips and tricks on jumps and drops. But they aren’t very stable on high-speed sections compared to frames with longer chainstays.
Measure the chainstay length from the center of your bottom bracket axle. And then go all the way to your rear dropout’s center section. The average chainstay length of mountain bikes is around 420 mm to 500 mm.
Measuring your Mountain Bike’s Head Tube and Seat Tube Angles
Your frame’s head tube angle depends on your mountain bike discipline.
Here are the major mountain bike disciplines:
Downhill bikes have a head tube angle of around 63 degrees. Freeride or park bikes have 62 degrees. Meanwhile, enduro bikes have around 65 to 66 degrees. These are considered slack.
The opposite then goes for cross-country bikes which have steep head angles. This makes it easier to climb uphill. Their usual head tube angle is around 68 degrees to 70 degrees. The head tube is the small tube that covers your fork’s trunk.
Meanwhile, seat tube angles for cross-country frames are around 74 to 75 degrees. Enduro bikes have 75 to 76 degrees. And downhill bikes have 76 to 77 degrees seat angle.
Measure your head tube and seat tube angle by downloading an angle app such as Angle Meter. Just tilt it and make it parallel with your head tube and seat tube. It will then automatically get the angle.
How to Measure Bottom Bracket Height
Then there’s the bottom bracket. It might come as the last, but it isn’t the least important aspect. In fact, this is very important to measure because it’s where your ground clearance depends on.
A higher bottom bracket height means better ground clearance. Meanwhile, a low bottom bracket gives you smaller ground clearance. This also means your frame’s lower portion is more likely to hit large protruding rocks and roots.
But note that high BB height compromises control. It also makes your bike less stable on high-speed sections. The opposite happens with a low BB height because you can have more control over high-speed sections.
This happens because your center of gravity is lower. You can measure the bottom bracket height by starting from the BB center to the ground. The average bottom bracket height is around 300 mm to 400 mm.
Learning how to measure a mountain bike frame is important. This ensures that you get the right bike size for you so you don’t compromise safety, comfort, and ride performance.
Just be sure the measurements you take are all accurate so you won’t get the wrong frame size. Note that sizing is a major factor in your skill progression. So, make sure to get the right size. You’ll surely be better, faster, and safer on your mountain bike when you do.
A writer by day, a tech enthusiast by night, and a mountain biker at the weekends.
After four years in business school and working for multinational clients, Jomar believes he can improve the world through his writings.
Jomar has six years of experience as a writer and has a degree in entrepreneurial marketing. Some of his works have been published on Blokt, Clutch Points, and iTech.