When you first start mountain biking, you may not realize the importance of bike fit. The first bike you buy generally is one that is approximately the right size for your height and weight, but its measurements have not been completely dialed into your exact specifications. But once you’ve gotten comfortable on that bike, it’s likely time for an upgrade – and with that upgrade, you need to get more detailed with your bike measurements in order to get the optimal ride. But why exactly is bike fit so important?
There are many reasons why getting the right measurements for your bike is important, and some may surprise you. Perhaps the most important reason is for injury prevention. If you head out on the trails daily or go for intense, multi-hour rides even once a week, you may eventually experience an overuse injury. Overuse injuries like knee pain and lower back pain are common, but having an improper fit for your bike’s saddle will make those injuries even worse. Additionally, that problem will never go away even with time resting off the bike, since it’ll come right back the second you head back out on the trails. Another important reason to get a proper fit for your mountain bike is handling accuracy. If a bike’s frame and wheels are too large for your strength and body size, then there’s a good chance that you won’t be able to control its movements as precisely as you would like. This could lead to some dangerous trail situations, especially around tight corners or on steep ledges.
Though the two reasons above are critical for comfort and injury prevention, there are multiple other reasons that you should understand how to fit your bike properly. However, these measurements can be difficult to understand – especially if you’ve never gone through the process before. Here, you’ll find some easy-to-follow tips and tricks for fitting and sizing your ideal mountain bike. There are three main aspects of a bike to measure: handlebars, tires, and frames. Of these, the most important is the frame – and within that, there are even more areas that need measurement. You’ll find all of the necessary terminology and definitions for each of these areas below, as well as the underlying reasons for measuring each of these parts.
How to Measure a Mountain Bike Frame
The frame of a mountain bike is the central structure that holds all of the other parts together. It’s what keeps the bike’s wheels attached and spinning, and what allows suspension systems to properly absorb pressure when necessary. Mountain bike frames typically are made of one of four materials: carbon fiber, titanium, steel, and aluminum. Each of these materials has different pros and cons, primarily related to durability, weight, and price. The frame also needs to be properly proportioned for your body, as it keeps the handlebars and seat in position for you to accurately control the bike.
Finding the right proportions and measurements depends on the type of frame you’re using. If you’re using a hardtail mountain bike, then the front wheel has suspension but the back wheel does not. This forces the front wheel to angle out more to accommodate the suspension, therefore making the base arm of the frame lie at an exaggerated angle. This shouldn’t change anything about your bicycle sizing methodology unless you’re picking out a seriously wild technology that has a different frame size. In those cases, bike shop owners will let you know. With that in mind, here’s how to measure a mountain bike frame properly:
1. First, stand with your legs comfortably apart and your shoes off. You want them to be about as far apart as they would be while you’re biking.
2. Measure the distance from the ground to the inseam of your pants, right at crotch level. You should measure this in both inches and centimeters, as different bike frame manufacturers will use metric or imperial units.
3. Calculate the right size for your frame using the following formula:
Measurement (in cm) x 0.66
4. Compare this final frame size to a bike sizing chart. You can find many of these online, and these will help you find any discrepancies in your measurements prior to purchasing a frame. This sizing chart will also help with fine-tuning adjustments based on your total height and not just your leg height.
How To Measure Your Mountain Bike Axle
If your wheels are creaking or your bike is generally feeling unstable the longer you spend on technical terrain, you may want to consider measuring your axle size. The axle is a critical component of your bike frame, allowing force to be distributed from the wheel into the rest of the bike. If axles are too thin or are asymmetric, parts can break easily. If you’d like to know how to measure bike axle size, follow these steps:
1. Remove a wheel from your bike. If you’re curious about the axle size of both wheels, remove both wheels.
2. Remove the axle from the wheel by loosening any attached nuts and bolts.
3. Use a caliper to measure the diameter of the axle. Generally, mountain bike axles are either 12mm or 15mm in diameter.
4. Use a standard ruler to measure the total length of your axle. This is the most important step, as replacements must be the exact length for the wheel to be functional.
5. Measure the over locknut dimension (OLD), or the distance in between the two sides of your fork. This lets you know how wide the axle can be inside the fork.
How To Measure A Mountain Bike Head Tube Angle
Earlier, I mentioned the angle of the front wheel and front fork. It’s actually important to monitor this angle if you’re aiming to be as efficient as possible. The part of the bike frame that connects the front fork and the handlebars is known as the head tube, and the angle is most commonly known as the head tube angle.
Different head tube angles allow you to navigate differently on a mountain bike. At a slacker head angle (positioned closer to the seat), the front wheel will be farther from the back wheel. This means that there will be better stability and less noticeable bumpiness, but steering is far less responsive and turns can’t be performed as tightly. With a steep head angle (positioned farther from the seat), the front wheel may appear tucked in and the bike will have a sleeker profile. You’ll get great handling, and hill climbs will be easier. However, small bumps will definitely be felt and you have a higher chance of crashing over the handlebars if you aren’t used to the angle. Now that you know some of the pros and cons of different angles, here’s how to measure the head tube angle in a bike frame of your choosing.
1. Find the rearmost point of your frame. This should be where the rear gearshift connects to your frame.
2. Find the head tube.
3. Brace your frame up against the wall with the rear point of the frame against the base of the wall and the head tube facing up.
4. Use a protractor or an angle app on your phone to find the angle that the head tube is extended from the wall.
How to Measure Mountain Bike Handlebars
Many mountain bikers just use the standard handlebars that come with their bike, not giving much thought to optimal widths and diameters of mountain bike handlebars. But you may want to consider both handlebar width and handlebar rise when purchasing separate handlebars. Handlebar width allows you to distribute weight over a standard base, giving you stability and leaning confidence. Handlebar rise is the difference in height between the center of the handlebars and the farthest tip.
If you’re curious about how to measure mountain bike handlebars in terms of rise and width, it’s actually surprisingly easy. For handlebar rise, simply grab a ruler. Use the ruler to trace a flat line out from the center of the handlebars, then measure the distance from the end of the handlebars to where they would be if the handlebars were completely flat. That distance is the amount of rise on the handlebars. Most handlebars are flat, but a few sets can have up to 2 inches of rise to give more flexibility on the trails. Handlebar width can simply be measured as the distance from one end of the handlebars to the other. Most handlebar widths run between 750-800mm.
How to Measure Mountain Bike Tire Size
The final important component of a mountain bike that must be measured is tire size. Your tires dictate the speed you can go, the traction you can maintain, and the terrain you can conquer. Mountain bike tires come in three main sizes: 26-inch, 27.5-inch, and 29-inch. 26-inch tires are nimble but tend to get stuck on large rocks and roots. Top-of-the-line downhill mountain bikes will have 29-inch wheels to make even the largest bumps smooth. However, 27.5-inch tires are gaining in popularity as they offer the best of both worlds for most riders. If you want to know how to measure mountain bike tire size, it only takes a few steps:
1. Flip your bike over so it’s resting on its handlebars and seat. Alternatively, rest it against the wall or use a kickstand.
2. Use a ruler or tape measure to find the distance from the center axle (see above for details on axle measurements) to the outer edge of the tire.
3. Double this measurement to find the overall diameter of your tire.
4. Measure from the center axle to the inner edge of the tire, but in millimeters.
5. Double this measurement to find a different tire size known as the ISO measurement. This is an international standard that ensures more rigorous definitions of tire size are used.
6. Use the tape measure to carefully measure the tire’s tread width from one side of the flat part of the tire to the other side. You can measure in both inches and millimeters, depending on which measurement system you’d like to use.
7. If you’re measuring in inches, round to the nearest inch. Most tire sizes are in inch or half-inch increments, so measurements slightly above or below will be rounded up or down.
Finding the proper bike sizes may seem like a difficult process. There are quite a few different parts to measure, and even then those measurements can feel like they aren’t quite right. But properly fitting your bike will ensure that you’ll be comfortable and injury-free for years to come. Furthermore, trained professionals at bike shops will happily double-check your measurements if you provide a short list for them to go over. The more comfortable you get with active measurements, the better your bike will feel – and the better your trail rides will be.