Mountain bike frames come in different sizes and knowing the essential measurements that make up the frame is key. If you are planning to buy or rent a mountain bike, this information is quite useful in ensuring you get a nice fitting bike that is comfortable to ride.
We will tackle the most important measurements that define the frame size of a mountain bike. The figures you will obtain will guide you choose a proper fitting mountain bike.
Ways on How to Measure a Mountain Bike Frame
We will explain the key measurements in the following key areas:
1. The Seat Tube Length and Angle:
• Seat tube length
This is the distance from the middle of the bottom bracket to the height of the seat tube.
Using a tape measure, place it at the center of the bottom bracket and run it to the top of the seat tube.
Record your measurements in metric units. The seat tube length is important because that is essentially the frame size of the bike.
•Seat tube angle
This is the angle in degrees between the seat tube and the ground. You can use a clinometer app to get the angle. This angle does not change significantly and it usually ranges from 71 to 75 degrees.
2.Top Tube Length:
This is the horizontal length from the center of the head tube to the center of the seat tube. The top tube length is achieved by measuring the effective top tube length/virtual top tube.
Use a spirit level and a tape measure to measure horizontally from the centerline of the seat tube to the center of the head tube. Effective top tube measurements are consistent even if the top tube is sloppy.
3. Bottom Bracket Height:
This is the length from the ground to the middle of the bottom bracket. This height affects the stability of a bike and an indicator of good clearance.
Ensure the bike is in an upright position and the tires are inflated. Use a tape measure to get the height in metric units. For stability, a low bracket height is ideal.it also improves bikes cornering ability.
The reach will guide you in knowing the horizontal length of a bike frame.
To measure the reach, you need a spirit level and a plump line. Attach the plump line to the edge of the spirit level, ensure it is in line with the center of the head tube.
Adjust the spirit level until you see that the plump line has intersected with the imaginary line that goes down to the center of the bottom bracket. Lastly, measure the head tube and the top of the plump line.
This is the distance between the bottom bracket and the top of the head tube.it indicates the vertical length of the bike frame.
Using a tape measure, take the height from the ground to the top of the head tube, and also the vertical length of the bottom bracket from the floor then subtract the two.
This is the length from the middle of the bottom bracket to the center of the rear axle. Simply use a ruler or a tape measure and measure from the side view of your bike. If your bike has horizontal dropouts, record the shortest distance.
Chainstay length is an important component of the wheelbase and also affects frame handling. A shorter chainstay will be more comfortable than a longer one.
On the other hand, a longer chainstay makes the bike more stable coming down. A 430mm-450mm on 29inch and 425mm-435mm n 27.5inch bikes are recommended.
This is the horizontal length between front and back axles. Ensure that the bike is upright and the bike fork is straight. Measure the length from the front to the back axle.
You will need to measure on both sides and do an average for accuracy. A longer wheelbase will make your bike more stable in terms of speed.
8.Stand Over Height:
This is the vertical length from the top tube frame to the ground. Most mountain bikes will have a slanting top tube hence varying measurements. To take the height, wear your riding shoes and stand in your best riding position. Mark the position, then take measurements from the top tube to the ground.
9.Head Tube Length:
This is the distance from the top to the bottom of the head tube. Just measure the length using a tape measure. A longer head tube will raise the front side placing you in an upright posture.
Frequently Asked Questions - FAQs
Q: What size of mountain bike should I get for my height?
Mountain bikes come with size charts that list different heights for different frame sizes. You need to measure your height and inseam. To get the inseam, stand with your legs apart then measure the height from the ground to the crotch.
Q: How are mountain bikes sized?
They are usually sized as small, medium, or large. The frame size is what differentiates them. Seat tube length will determine the frame size. However, mountain bikes have come in different shapes hence seat tube length less useful. Manufacturers will recommend a bike size basing on one's height.
Q: which MTB wheel size is best for me?
There is the larger size (29 inches) and the smaller wheel (27.5 inches). Each size has its advantages. For example, smaller wheels are strong and light hence well for changing speeds. They are also for smaller riders. Larger wheels on the other hand are good for rough terrain and perfect for racing. They are suitable for bigger riders.
Q: Are frame sizes different for women-specific mountain bikes?
Yes, women's frame sizes are smaller but the sizing is calculated the same way. Manufacturers will alter frame sizes to give women a good fit. On average, women tend to be shorter than men hence their bike will have a short stack height.
We have discussed the different measurements that should be considered and how to go about it. These measurements will help you in choosing a mountain bike that is comfortable and is perfect for the kind of riding you choose to do.
Hello Guys! I am John Reese, a professional biker and my hobby is biking! I have been biking for last 10 years and I love using bikes while outing as well. Based on my experiences with the different type of bikes (mountain bikes, road bikes and hybrid bikes); I am sharing my opinion about various bikes so that a beginner can get started right away. Happy reading!