How to Choose Mountain Bike Fender Width Properly – Tips & Tricks

If you would love your clothes and your bike to be kept clean during and after cycling then you need to install mountain bike fenders on the rear and front of your bike. They save you the stress of having to wash your dirt-stained clothes and bike after each riding session. That’s why some people only ride on dry trails. But with fenders, you don’t have to worry about the condition of the road, as long as you are able to match the mountain bike fender width with your mountain bike tires

Choose mountain bike fenders that are 10-12 mm wider than the tire to prevent water and mud splashing. Fender tire clearance should be 10 mm for road riding and 15-20mm for trail riding.

To match a mountain bike fender width with the right mountain bike tires, first, determine the fender width on the specifications document, and then match the fender width with the mountain bike tire width printed on the side of the tire. 

Whether dry or wet, cycling will always be enjoyable. A fender protects you from the splashes and sprays of water, mud, or grime whenever you ride through a puddle or on wet trails. Fenders not only protect you, but they also prevent parts of your bike like the chains, derailleur, and brakes. To learn more about the benefits of using fenders and how to extend them to add extra coverage read our article about tips for choosing mountain bike fender extensions

Your mountain bike fender width should protect you from mud and other debris being flung up
MTB fenders protect your clothes and bike frame from water and mud splashes when riding. Image source: Carousell.

How Wide Should Bicycle Fenders Be?

Your bicycle fender needs to be wide enough to allow good clearance between the fender and the tire.  Tire clearances basically refer to the spaces between the tire and any other non-wheel component of your bike. 

Bicycle fenders should be 0.3-0.4 inches or 10 -12 mm wider than the tire's width to shield any radial water or mud sprays from striking the rider while also preventing the tires' sides from rubbing against the fenders.

Your fender needs to be wide enough to prevent the chances of any object getting stuck in between the tire and fender as well as prevent the tire from rubbing against the fender when the path gets bouncy. As this article from SAE International explains, you also want to install a  fender that won’t negatively affect the aerodynamic drag of the bicycle.  A rule of thumb in fender fitting is to make sure the fender is at least 8mm wider than the tire. Having a fender that’s 10-12mm wider than the tire is usually ideal. 

Let’s say you’re using a 40mm tire, you will need to install a 50-52mm fender. The wider the clearance provided by the fender, the less the chances of you having to constantly remove sticks, stones, or other debris which may be stuck in the wheel of your bike, and the better the protection. Full-length, close-fitting fenders like these clip-on fenders offer full protection of your clothes and shoes from spraying water and other debris that gets flung up from your bike tire. If maximum coverage and protection are what you’re looking for, they are a good pick that will protect you well. This article from IOP Conference Series on Materials Science and Engineering discusses the innovative design of mountain bike fenders and how they aid in riding safety. 

List of Mountain Bike Tire Sizes and Their Matching Fender Width:

Mountain bike tire size Matching mountain bike fender width Example of fender
700c × 35mm tires 45mm wide Planet bike cascadia bike fenders
26 inches × 2.1-2.35 inches tires 65mm wide SKS P65 silver chromoplastic longboard
700c × 38-47mm tires 53mm wide SK B53 commuter 2 bicycle fender set
24-29 inches × 1.50-2.35 inches tires 50-88mm wide RBRL Bike mudguard bicycle fender
650B × 48mm tires 75mm wide SKS Bluemels 75 U Fahrrad-Schutzblech
650B × 38mm tires 59mm wide Mucky Nutz, MugGuard

You might also find interest in learning about these five key mountain bike fender parts, along with their functions and pictures. So be sure to check that related article out too.

How to Match a Mountain Bike Fender with a Mountain Bike Tire before Installing

The width of your mountain bike tire is usually printed on the side of the tire. The fender should be at least 10-12mm wider than your mountain bike tire in order to prevent it from rubbing against the tire and to also give you maximum coverage and protection from mud, stones, and other debris that might be flung up by the tire onto the rider.

To match a mountain bike fender with a mountain bike tire, ensure the fender length is long enough to extend down the tire size to the 3 o'clock position, and the bike tire and fork clearance are wide enough to accommodate the fender width. For fat-tire bikes, the shape and width of the rear fender should match the width of the bike tire. Most importantly, make sure that the fender is 8-12mm wider than the width of the tire.

To properly match a mountain bike fender with a mountain bike tire, you need to ensure that the fender is long enough to extend down the tire size to the 3 o’clock position. You can find the radius of your tire written on the side. This gives you the proper coverage and protection from splashing water, mud, and grime.  There also needs to be enough fork and tire clearances for the fender to fit properly without rubbing any part of the bike. Our article about how to install mountain bike fenders will help you position the fenders so that they don’t catch on the tires.

Check the walls of your tires for their size so that you can match the correct mountain bike fender width with them.
The diameter and width of the bicycle tire are indicated on the wall of the tire and measured in mm. Image source: mybiked.

Tip 1. Ensure the Fender Length Is Sufficiently Long Compared with Tire Size

There are some important factors that should be taken into consideration when selecting the fender that will be the best fit for your bike. We have talked about one of them; the width of the fender. Another important factor is the length of the fender.  The greater the length of your fender, the better the coverage. The long length of this bolt-on fender for example is what makes it the most durable, most secure, and cleanest option against grime, mud, and debris.

A long fender will be more effective at directing the water away from the bike toward the ground—preventing your legs, feet, and lower back from being soaked by water or getting muddied. Since a long fender provides more deflection of water, grime, and debris, your bicycle components like the chain and drive-train that are exposed will be protected. This increases the durability of these bike components and lowers the cost of maintaining and replacing worn-out bike parts as we explain in our article that explains how to replace a chain on a mountain bike. You may however not like the new look a longer fender will be giving your bicycle, if this is the case, then mudflaps or mudguards like these are a good option.

Mudflaps also catch dirt that flings up with your tire rotation, preventing it from splashing on the rider. They can be attached to both the front and rear tires. While you’re ensuring that the length of your fender provides you maximum protection, do not forget to check the radius of your tire. Check the side of the tire for this. 

Many bikes such as road, gravel, and commuter bikes use 650b and 700c to indicate their tire radius size while mountain bikes use the following tire radius sizes: 26-inch, 27.5-inch, or 29-inch. Read our article about choosing mountain bike tires for maximum grip to learn more about the vast variety of tires available. It’s true that long fenders provide better protection, but the length of the fender will matter less if the tire is wider than the fender. Always remember the basic rule of fender fitting, your fender must be at least 8-12mm wider than the tire.

Fender stays are used to attach bolt-on fenders to your bike so that they are secured with enough space between the tire and the fender.
A bolt-on fender uses fender stays to ensure there is sufficient tire clearance. Image source: Bicycling.

Tip 2. Ensure That the Brakes and Crown Provide Enough Space to Attach Wide Fenders

A bicycle fork is made up of two pipes that are joined at the top by means of a fork crown. The main function of your bicycle fork is to attach the front wheel of your bicycle to the frame. The tire and fork clearance is the most important factor that determines whether a fender can be fixed on your bike or not. This is because, without sufficient clearance, you’ll encounter a lot of problems, some of which can have a direct impact on rider safety. Our article about adjusting fender offset discusses how to ensure your fender is properly positioned to enjoy a safe ride. 

Ensure you have enough fork clearance to attach a mountain bike fender.
To have sufficient clearance to attach a mountain bike fender, ensure you have at least 10-15 mm between your tire and your crown. Image source: Singletracks.

Firstly, you need to determine what the best clearance for your bicycle is but this article by Sim-works recommends 10-15mm depending on the type of bike. This tells you that you can install a fender. Next, you have to figure out the fender width.  

To determine the fender width, you will have to check the clearance at the brakes, in the fork crown, and between the seat stays. To check for the brakes, press the brake lever so that the pads touch the rims. Then measure the width between the arms, and ensure that you have at least 9-10mm spaced vertically from the tire to the brakes. Short-reach brakes normally fit 35-37mm fenders while long-reach brakes can fit 43-45mm fenders. 

Next check the height and width of the fork crown. You also need to ensure that the seat stays are a suitable distance apart and that the brakes bridge is at least 10mm above the tire. A distance of about 20mm is ideal between the tire bridges and fork crowns. Since you don’t have any bolt head extending inside the fender at the sides of the tire, a distance of about 6mm-10mm will be okay. Our article that provides tips and tricks to choose clip-on bike fenders for mountain bikes is an excellent resource for learning more about fender spacing on mountain bikes. 

Though fenders with tighter clearances can still be installed, they would produce a rubbing effect between the tires and fenders which will wear down your tires more quickly. And if during the course of riding, objects like stones, sticks, and pebbles are picked up by the tire, they could damage the fender, causing it to collapse which may cause you to crash. If the clearance gap is not enough, the size or width of the tire can still be reduced to create more room for the fender to be installed.

Ramp up your safety by matching your fender widths with your mountain bike tire sizes for optimum protection.
MTB fenders with good tire clearance and adequate coverage against water and mud ensure a safer ride. Image Source: Amazon.

Tip 3. Rear Tires Are Narrow. Make Sure The Bike Tire Is Narrower Than the Width of the Rear Bike Fender

The rear tire of mountain bikes is often narrower than the front tires. This is to allow the tire to roll faster and accelerate quicker because it reduces rolling resistance. Since the rear tire is most likely to cause your buttocks and lower back to be stained with mud and water, you need fenders that would be wider than the rear tire. Ideally, your rear fender like this one should be 8-12mm wider than your tire in order to enjoy maximum coverage.

Tip 4. Front Tires Are Wider. Match the Front Bike Tire and Crown Clearance with the Fender Width

The front tires are often wider. The increased width provides the rider with more traction for turning, which improves the steering and maneuverability of the bike. 

While a fat front tire can help in traction and movement in rough terrain, you want to make sure the tires aren’t too wide or they will start rubbing against the frame. That is why you need to check the user manual to know the maximum tire size that’s going to be compatible with your bike.

When the gap between the tire and the fender (or fender clearance) isn’t constant throughout the tire circumference as a result of the tire being fatter than normal, it will not only affect the bike’s appearance but also make it difficult for you to get the right fender that will fit your bike and hamper safe handling on rougher terrain. Our article on common mountain bike grip upgrades & how to choose the ones you need has a helpful section about recommended tire upgrades for particular types of terrain. 

How Much Clearance Should There Be Between Bike Fenders and Tires?

For your fenders to do what they are supposed to do it is important that you check the clearance between your bike fenders and your tires.

The clearance between a mountain bike fender and the tire should be 10 millimeters. For a muddy trail, the best clearance is 15 – 20mm because a larger fender clearance prevents mud from getting stuck between the fender and tire. 

Here we break down what clearances you will need for different riding conditions:

Riding Conditions Clearance Between Bike Fenders and Tires
Commuting on a Sunny day without mud 10 mm
Commuting on a rainy day on tarred roads 10 mm
Downhill riding on muddy trails after rain 15-20 mm
Riding on uneven trails with rocky paths 15-20 mm

Minimum Spacing Needed When Fitting Mountain Bike Fenders   

There are other parts of the bike that need particular spacing for the bicycle to provide a comfortable and safe ride.

When matching mountain bike fender width, ensure that the minimum spacing between the tires and fork is at least 5 mm. The minimum spacing between the brake caliper and wheel should be 23 mm. 

Here we break down mountain bike spacing areas that need to be checked:

Mountain Bike Spacing Areas to Check Minimum Spacing
Spacing between tires and fork 5 mm
Spacing between the brake caliper and wheel 23 mm

How to Adjust Mountain Bike Fenders - Front Fenders

With properly installed MTB fenders, you can enjoy riding in any condition. You don’t have to worry about the wetness or dampness of the road because with fenders you’re sure of having a pleasurable cycling session. With the detailed practical steps outlined in this article, you can certainly choose the fenders that will perfectly match your bike tire and give you the best cycling experience.

To adjust a mountain bike's front fender first loosen the screw on the crown of the fork. Next loosen the screws that fasten the side of the fender to the fork sides. Finally, adjust the fender so there is adequate clearance of at least 12mm and fasten the fender in this position by tightening all three screws. 

Here we list the steps to reposition your fenders so that they don’t touch your mountain bike’s tires:

Step 1. Loosen the Screws on the Front Fender

This is the first step of the adjustment process where you loosen the screws that are holding the front fender to the fender strut by turning the Phillips screwdriver in an anti-clockwise direction. When adjusting the fender it isn’t necessary to completely remove the screws, simply loosening them will allow the fender to be maneuvered into the correct position.  

Step 2. Reposition the Front Fender

Once the screws have been loosened, gently reposition the front fender until it is properly positioned over the tire.

Step 3. Reattach the Fender

When the fender has been properly positioned, tighten the fender screws by turning them in a clockwise direction using the Phillips screwdriver. Ensure the screws are tightened well to prevent the fender from moving during the ride, or possible accidents that may occur as a result of loose screws.

How to Adjust Mountain Bike Rear Fenders

To adjust mountain bike rear fenders so that they don’t rub on the tires first use a Phillips screwdriver to loosen the screw that attaches the fender to the back seat stays. Next, reposition the rear fender so that there is at least a 12mm gap between the fender and the tire, and tighten the screw to keep the fender in this new position. 

Step 1. Loosen the Screws on the Rear Fender

To adjust the rear fender of your bike, you first have to unscrew the screws, turning them in an anticlockwise direction.

Step 2. Adjust the Rear Fender

When the screws are loose, reposition the fender in a way that would prevent it from rubbing against the tire. Some rear fenders are longer than front fenders, so you have to make sure the rear fenders are properly aligned.

Step 3. Fasten the Rear Fender in Position

When you are sure that the rear fender has been properly positioned, tighten the screws holding the fender to the fender strut by turning it in a clockwise direction. Ensure the screws are well-tightened. Ensure that there is enough fork, tire, and fender clearance.

Front and rear fenders on your mountain bike will ensure that your bike has less wear and tear and that you stay clean and safe on your cycling adventures.
Rear and front fenders not only protect the rider and bike against mud and water but also add a sport and adventurous look to a mountain bike. Image Source: Amazon.

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