It’s possible to install gravel tires on an MTB when the frame and fork support disc brakes and have clearance for 27.5″ or 28″ wheels.
Gravel Tire Size
Gravel tires come in two main sizes – 27.5″ and 28″. Therefore, the mountain bike that you would like to equip with gravel tires should have clearance for at least 27.5″ wheels.
Some 27.5″ MTBs will be able to accommodate a 28″ gravel tire, especially if it’s slimmer, but it’s best to match the original tire size of the MTB to that of the new gravel model to avoid compatibility issues.
FAQ: How will a 28″ gravel tire fit on a 29″ rim?
29″ MTB wheels and 700c/28″ gravel and road wheels use rims of the same diameter, namely 622mm.
In this case, 29″ describes the size of the overall wheel rather than the rim. And since MTBs have much wider tires than gravel and road bikes, the wheel diameter is larger too. The rim, however, remains the same size.
Brake Compatibility
If you want to use a wheel size that’s different from the original, the bike will have to answer the following criteria:
- Clearance. The fork and frame should have enough clearance if you’re going a size up.
- Disc brakes
Wheel size changes do not work well with rim brakes because the rim ends up below the brakes shoes when “downsizing” and above the brake shoes when going a size up. As a result, the brake can’t grab the rim.
That issue can be circumvented by moving the brake bosses up or down via adapters or by re-welding them to a different spot. However, in both cases, the procedure is expensive and in some situations, it may be wiser to sell the bike and purchase the one you really want.
For that reason, it’s recommended to change the wheel size only when the bike uses disc brakes.
Disc brakes do not create the aforementioned problem because the brake rotor always attaches at the same place (the hub) and thus the overall rim size is irrelevant from the perspective of the brake.
For more information on this topic, check out the following articles:
Can You Put 27.5” Wheels On a 29” Fork and Frame?
Can You Put 29-inch Wheels On a 27.5-inch Fork?
Rim Width
Gravel bike tires are narrower than the MTB models used on trails. Subsequently, in some extreme cases, the rim of an MTB wheel may end up being too wide for the gravel tire.
When the rim is too wide, the user won’t be able to properly secure the tire to the rim.
To avoid this problem, search for a label on the rim specifying the minimum tire width that the rim can accommodate. You could also search for the rim model online or contact the shop that you’ve bought it from.
Do You Really Need a Gravel Tire?
Before purchasing a gravel tire for an MTB one has to ask themselves whether such a switch is even necessary.
The main difference between standard MTB tires and gravel models is the tread.
The tread of most gravel tires is less aggressive because gravel terrain doesn’t benefit from extra-large knobs.
Contrary to popular belief, tire knobs do not always increase grip. Their usefulness diminishes as the smoothness of the road increases. Knobbies improve grip only when they can dig into the ground. For that reason, commuting bicycles and road bikes continue to rely on slick tires.
Slick tires provide more grip on smooth surfaces because the contact patch with the ground is greater. In different, when knobby tires are used on asphalt, only the knobbies touch the ground. The outcome is reduced grip and increased rolling resistance.
The downside of slick tires, on the other hand, is that they are very slippery on off-road terrain.
As one can imagine, gravel tires have to be somewhere in the middle. They have to provide some off-road grip coupled with decent rolling resistance.
That’s achieved by adding a light tread pattern to the middle of the tire and combining it with fairly aggressive edges meant to grip the gravel surfaces during cornering.
Having said that, such tires have been available for light cross country races since the beginning of the sport.
If the user puts XC tires with low rolling resistance on their MTB, one could count it as a legit gravel tire even though it isn’t officially labeled as such.
The Pros Of Adding Gravel Tires To an MTB
- Reduced Rolling Resistance
The main motivation to install gravel tires on an MTB is to reduce the rolling resistance of the tires when riding on gravel and smooth surfaces.
The lower rolling resistance makes it easier to reach and maintain a higher speed.
- Gravel Experience Without Getting a New Bike
n an MTB won’t turn it into an actual gravel bike, they will offer a partial feeling for the adventure.
- Potentially Lighter
Since gravel tires are narrower than MTB models, some of them are also lighter. That said, the weight savings aren’t spectacular and shouldn’t be an incentive to get new tires.
While a set of gravel tires on an MTB won’t turn it into an actual gravel bike, they will offer a partial feeling for the adventure.
- Potentially Lighter
Since gravel tires are narrower than MTB models, some of them are also lighter. That said, the weight savings aren’t spectacular and shouldn’t be an incentive to get new tires.
The Cons of Installing Gravel Tires On an MTB
- Questionable benefits
Truth be told, basic MTB tires will perform decently well on gravel, especially if they’re designed for cross-country riding. Sure, they may not be as fast as dedicated gravel models, but this wouldn’t matter to a recreational rider.
If you’re unsure whether the expense is worth it, simply take your bike to the local gravel trail and make a test run.
- Negative Changes to The Geometry
If you decide to switch to a different wheel size (not always recommended), the original geometry of the bike will change and so will the handling.
