We don’t need to tell you how important wheels are for any bike. Having the right wheelset for your mountain bike will allow you to deliver your best performance. It will also let you enjoy your time on the trail even more than you already do. There is a lot more technical information to consider for wheels compared to other bike components. In this article, we have tried to provide you, as simply as possible, all the things that matter when buying new wheels.
Bike Wheel Components
Before you think about buying a new set of wheels, you should become familiar with the different parts that make up a wheel. There are other smaller components as well, but the following are the main ones.
- Rim: This is the outer part of the wheel which runs around the circumference. Its main function is to hold the tire in place.
- Hub: This is the centerpiece of the wheel around which the wheel rotates. The wheel axle passes through the hub. It contains attachments for a rotor if it is a disc brake wheel. The rear hub also has an attachment for the freehub.
- Bearings: The bearings allow the hub to rotate freely on the axle of the wheel. There mainly two types of bearings – cup and cone bearings, and cartridge bearings.
- Spokes: These are the rods connecting the rim to the hub. The number of spokes and the arrangement pattern may vary to instill different properties. Spokes are almost always kept in tension.
- Nipples: These are small nuts that attach the spokes to the rim. They can be turned to adjust the tension in the spokes.
Mountain Bike Wheel Buying Considerations
There are a bunch of factors that you need to take into account before getting some new wheels for your mountain bike. In general, you should look for lightweight wheels if you are into cross-country racing. For downhill riding or dirt jumping, your main focus should be strong over low weight. All-mountain or trail riders should look for wheels that provide a good combination of low weight and strength.
The size refers to the diameter of the wheel. When it comes to mountain biking, most wheels come in one of three sizes – 26”, 27.5” (650b), or 29” (29ers). There are also smaller and larger MTB wheels but they are far less common. Wheels with a smaller diameter are lighter and have a lower rotational mass. This allows for quick acceleration and better cornering. They are also stiffer than larger wheels.
The bigger a wheel gets, the larger the contact area of the tire with the ground. This leads to better traction for loose and muddy ground. The ability to handle bumpy terrain is also improved with larger wheels. Take these and your riding style into account to decide which size is best for you.
On mountain bikes, you will find two types of rims according to what kind of tires they can fit. The first is a standard rim which is meant to be used with a clincher type tire. Here, an inner tube is used which is inflated inside the tire. This is a simple design and allows for easy fitting and replacement. Clincher tires are run at higher pressures to reduce the likelihood of pinch flats. The higher pressure reduces rolling resistance but does not provide as much traction as might be required on some trails.
Nowadays, most wheels use tubeless or tubeless-ready rims which can accommodate both clinchers and tubeless tires. Tubeless tires are the better option for mountain bikes in most cases. This is because they do not have an inner tube and so pinch flats do not occur. And small puncture flats are taken care of by a liquid sealant poured inside the tire at the time of setup. Additionally, they can be run at lower pressures which offer better traction. The initial setup is a bit more complicated with tubeless tires but changing tires is a lot faster.
Recently, the trend has been for tires and consequently rims to get wider. Even though a narrow rim is lighter, it has less grip on the ground than a wide rim. A rim can actually fit a wide range of tire widths. However, it is better to not pair a narrow rim with a wide tire. Doing so will reduce cornering traction because the outer knobs sit too high up the sides. Also, wider rims produce a flat square base which is more stable and has improved traction. The following table will give a rough idea about how to pair up tire widths with rim widths.
|Rim Width||Tire Width|
|23 - 25 mm||2 - 2.25 inches|
|25 - 30 mm||2.25 - 2.4 inches|
|30 - 35 mm||2.4 - 2.6 inches|
|35 - 40 mm||2.6 - 3 inches|
Bike wheel rims can be made out of either aluminum or carbon fiber. Aluminum, also known as alloy, is the more common and cheaper option out of the two. They are great for entry and mid-level riders. Carbon rims have a premium price tag but this is gradually decreasing. The structure of carbon makes the rim stronger and lighter at the same time. This is why they are increasing in popularity. Other than the high cost, the downside of carbon rims is that they are stiffer and hence, slightly less comfortable over rough ground.
Axle Types and Sizes
Traditionally, most bike wheels made use of quick-release (QR) skewers. They have a 9 mm diameter at the front and a 10 mm diameter at the rear. All bikes with a QR have the same sizing for the axle.
If your mountain bike’s model is not too old, then it is likely to have thru-axles instead of a QR skewer. Thru-axles are preferred due to the better strength and control that they provide to the wheels. On the front wheel, the axle width is usually 100 mm with a 15 or 20 mm diameter. On the rear wheel, the axle has a diameter of 12 mm and a width of 142 mm.
Modern high-end mountain bikes now have even wider axles called the Boost standard. These impart even more stiffness to the wheels. They measure 110 mm on the front and 148 mm on the rear. You can also get Super Boost rear axles which can have a width of more than 150 mm. To find out what axle width you need, simply measure the width of the wheel’s hub.
When it comes to spokes, the number, pattern, and even the profile of each spoke can vary from wheel to wheel. Each variation imparts slightly different properties to the wheels. There is no standard spoke pattern but three-cross and two-cross patterns are the most common. There are also radial spokes that reduce weight but also reduce strength. Spokes attach to the hub in either a straight pull pattern or, more commonly, a J-bend pattern. There is not much difference between the two.
The number of spokes can vary between 24, 28, 32, and even 36 in some mountain bikes. A higher number of spokes translates to enhanced strength and durability of the wheel. But it comes at the cost of more weight. The profile of the spokes can be of two types – circular or aero. Circular spokes are either butted, meaning it has variable diameter along the length, or it could straight gauge (of a single diameter). Aero spokes, aka flat or bladed spokes, have better aerodynamics as they cut through the air better.
Brake Type and Attachment
Rim brakes are now rarely used on mountain bikes. But if you do use it, make sure that you have the right brake pad type for the right rim material. Disc brakes have now become the mainstay on MTBs. The rotor of a disc brake attaches to the hub in one of two ways – six-bolt or center lock. Ensure that your wheel hub and disc brakes are compatible with each other.
Freehub and Engagement Speed
The freehub is a splined metal component to which the cassette is attached. It itself is mounted onto the rear wheel hub. The freehub also allows you to stop pedaling without having to bring the bike to a halt (coasting). You cannot just use any freehub with any cassette/drivetrain. You must check the compatibility which will be mentioned by the manufacturer.
The engagement speed refers to the number of degrees traveled by the pedal crank before the freehub engages to rotate the wheel forward. Faster engagement means more points of engagement and faster transfer of power. Slower engagement or fewer points of engagement mean better durability as the teeth are bigger. Whether you use faster engagement or slower is completely up to personal choice.
Frequently Asked Questions
Q1. What is a ‘true’ wheel?
Ans.: A wheel is said to be true when it rotates straight without any wobble. A wheel can become out of true when there is unequal tension among the spokes. This causes the wheels to wobble and greatly hampers control of the bike. The wheel can be brought back to true by adjusting the tension in the spokes. This is done by tuning the nipples.
Q2. Does the amount of tension in the spokes matter?
Ans.: There is a safe range within which the spokes’ tension should remain. If it is too low, the spokes might get ejected or the wheel might collapse. Too high and the wheel gets stiffer than usual. The most important thing to keep in mind for tensions in the spokes is that they should always be equal. Otherwise, the wheel gets out of true as discussed before.
Q3. Which type of bearings is the best for a wheel?
Ans.: There are two main types of bearings. Cartridge bearings have small needles or balls that are sealed inside. These bearings are found in more expensive bikes. They are quite easy to replace when worn out. The cheaper option is a cup and cone-bearing. This type can be serviced at home quite easily. However, the adjustment can be more difficult. Bearings also come in two different materials – steel and ceramic. Ceramic bearings are pricier but they are also stronger and have less friction. If you want the best performing option, it would have to be ceramic cartridge bearings.
Wheels are a bit more complicated compared to most other components of a bike. There are plenty of considerations before buying one. However, the time that you spend now will be worth it in the long run. If you are facing any trouble, don’t be shy to ask for help such as from your nearest bike shop. Getting the right set of wheels can greatly enhance your riding experience and significantly improve your performance.