What's the Purpose of the Rim Groove in Your MTB Wheel

Groove in Bike Wheel Rim

You may have noticed some grooves on the rims of your mountain bike wheels.

Since it's easy for you to observe when the rubber brake pads in your V brakes are worn out, it's not as easy to notice when the wheel rims have gotten too thin. That's what the grooves tell you.

The bicycle wheel rim deteriorates just like any piece that is subjected to constant contact and friction with another piece (brake pad). This is true especially if you ride a lot on muddy singletracks - sand, mud and other abrasive materials caught between the brake pads and the rims accelerate wear and tear. Of course, if your MTB has disk brakes, you won't confront with these issues.

So what you need to do is to check the rims regularly as to see if the grooves are still visible. If the rim has gotten flat this means it's time to replace it with a new one (or buy a new wheel altogether). This will prevent the rim to get too thin (so thin that the tube becomes visible - it might even explode). Basically, the excess aluminum on the rim (in which the groove is carved) acts as a wear and tear meter. 

Groove in Bike Wheel Rim
Groove still visible in my rear wheel - OK!

Flat Bike Rim - No Groove
Front wheel needs to be replaced - the groove is no longer visible
 NOT OK! (the rim is worn out)

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  1. I never asked myself what's the purpose of that groove. I thought it was just for design , but now it seems right what you are saying, but i doubt that the tube could become visible and explode, because most of the wheels (and i think all of those that have that groove) have two layers of alloy in that area (just for structural resistance).

    Another reason i think it is kind of impossible to see the tube is because when the rim will get too thin it will lose all its structural resistance and it will bend when passing over a bump, so the regular user will be determined to change it way before he will have "consumed" the entire layer.

    Regarding the disk brakes, the disks also gets thinner but due to the material from which it's made, the amount that has been worn it's not visible just by looking at it.

    But in the case of disk brakes it is, again, impossible to wear all the disk, because when it will get thinner it will deform (especially when they are hot because of a long braking period and then you pass through water and mud making them get cold very fast), resulting in brake vibration and inefficiency. So the regular user will be determined to change the disks because of their improper behavior waaaay before total wear.

  2. The exploding tubes are just reported events - it is possible though.

    Good points on disk brakes issues!


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