How to Measure a Mountain Bike Frame
Whether you are buying or selling a mountain bike, it is important to be able to determine the frame size. The frame size is one of the ways that one can determine the size of a bike and whether it is a suitable fit for them. it is therefore crucial for you to be able to determine the size of a frame. Otherwise a bad fit may result to bad posture and consequently pains, energy and speed inefficiency.
The heart of a good mountain bike is a good frame. The frame is the skeleton that holds together the other parts of a mountain bike.
There are numerous mountain bike models and styles in the market. Although there are standard mountain bike frame sizes, all mountain bikes are not equal. Knowing how to measure a mountain bike frame is key to choosing the right bike for you. Different frames are made from different materials including carbon fiber, aluminum, alloy and steel. Frame materials determine the sturdiness of the bike frame.
There are various charts that are used to compare frame size against a cyclist’s body measurements to determine an appropriate mountain bike. In addition, you can use frame geometry to determine the size of a mountain bike.
Here is how to measure a mountain bike frame
To determine the size of a mountain bike frame, there are key dimensions that you should be able to determine. These measurements are seat tube length, top tube length, slopping top tube length, top tube length and head tube length.
The measurements can be in either centimeters or inches depending on what works for you. Before beginning to take your measurements ensure that the bicycle is level so that the front and rear wheels are elevated to the same level.
Seat tube length
Seat tube length is basically the length of the seat tube. it is the distance between the center of the crank and the joint of the seat tube and the top tube.
Top tube length
The top tube length is the length of the top tube. The top tube is the main tube connecting the seat tube and the head tube. To measure, place a tape measure at the center of the tube joining the head tube to the top tube. Extend the tape measure until the joint of the top tube and the seat tube. Record the measurement in cm or inches.
Head tube length
Head tube length is the length of the head tube. Using your tape measure take the measurement between the joint joining the top tube and the head tube; and the joint where the front fork meets the head tube.The head tube length determines how high or low a cyclist is on the handlebars. The head tube length is the same whether your mountain bike has a sloppy frame or a traditional frame.
Sloping top tube length and sloping seat tube
If you have a sloping top tube you will need a spirit lever and a tape measure. Ensure that the front and back wheel are elevated to the same level. Using the spirit lever, determine a straight line from the joint at the head tube and the front fork to the seat post. Mark the seat post for where the straight line meets it. Use a tape measure to measure the distance between the head tube and front fork joint and the mark on the seat tube.
Similarly, to measure the slopping seat tube, use a tape measure to measure the distance between the center of the crank bolt to the mark on the seat tube made previously when measuring the sloping top tube.
Using frame size chart
Once you have the above measurements, you can use a frame size chart to determine what frame size is suitable for you depending on your length.
| Rider Height | Traditional | Semi Compact | Compact | |||||||
| Feet & Inches | Centimeters | Top tube | Seat tube | Top tube | Slopping Top tube | Seat tube | Top tube | Slopping Top tube | Seat tube | |
| 5’3’’-5’5’’ | 160-165 | 52.5 | 51.5 | 51.5 | 52.5 | 50.0 | 48.0 | 52.0 | 42.0 | |
| 5’5’’-5’7’’ | 165-170 | 54.0 | 53.0 | 53.0 | 54.0 | 51.5 | 51.0 | 53.0 | 46.0 | |
| 5’7’’-5’9’’ | 170-175 | 55.5 | 54.0 | 54.0 | 55.5 | 53.0 | 54.0 | 56.5 | 50.0 | |
| 5’9’’-5’11’’ | 175-180 | 57.0 | 55.5 | 55.5 | 57.0 | 55.5 | 56.0 | 58.5 | 54.0 | |
| 5’11’’-6’2’’ | 180-185 | 58.5 | 58.0 | 57.0 | 58.5 | 57.5 | 59.0 | 60.0 | 58.0 | |
Medium, small and large frame sizes
The most common mountain bike frames are 15-inc, 17-inch and 19inch sizes which are normally small, medium and large respectively. Other sizes include extra small and extra large. More details on the denotations of frame size are provided in the chart above.
Different manufacturers have different frame size sizing systems. Generally, round up your frame measurement to the nearest inch and compare to the manufacturer listing. Frames sizes are usually in 2-inch increments. In regards to the various frame measurements, while one manufacturer may quote say 17-inch frame with a 22-inch top tube another manufacturer may have a 17-inch frame with a 23-inch top tube.
The key to finding your suitable frame size is to test drive the mountain bike. Now you know how to measure a mountain bike frame for your next purchase or sale.
