18

Two days ago I installed a new pair of Schwalbe Pro One Race Addix (tubeless setup) and went for a first ride yesterday. Today i saw that both tires had some (5 or 6) perfectly round little holes evenly distributed all around the tires tread which I didn't see when installing them. Are those holes meant to be there anf if so, what are they for? Or did I damage them on my first ride?

picture of holes

30

It is an increasingly common practice for manufacturers to add tire wear indicators, which are little divots like the ones on your tire. Otherwise, there is no objective measure of when to change a tire apart from your mileage log (and riders of different weights should be expected to wear out tires at different rates). Basically, once you can no longer see the holes, you should toss the tire.

Perhaps you already know this, but you can then rotate your front tire to the rear. One should not rotate tires as we do in cars, because our rear tires wear a lot faster. I always knew this in theory, but seeing this happen with the wear indicators really cemented the concept. In any case, you want the freshest rubber on the front for control. However, rotating a very lightly worn front tire to your rear wheel is perfectly fine.

In principle, this type of wear indicator could also be useful on rim brake rims. I have not seen them as often, however. The Pacenti SL23 rim definitely had them, but that was a bit of a niche rim. Otherwise, one has to estimate rim wear via calipers or by seeing if the brake track has become concave. The increasing adoption of disc brakes may mean that manufacturers won’t bother with these indicators, because disc rims don’t take wear per se.

Just in theory: what happens if you ride the tire after the wear indicators are gone? Remember that tires have a rubber tread, which is glued to a carcass made of rubber, cotton, or perhaps other materials I’m not aware of. (Illustration at Schwalbe tires.) If you wore off the tread entirely, you would now have either the puncture protection layer (if present; some racing tires may forego one) or the carcass itself in contact with the road. I am not an engineer. However, the carcass materials were designed to hold a shape, and not to contact tarmac. I would expect grip to go down substantially, and I would not expect the carcass to be durable in that manner. Once you wore out the carcass, you would presumably tear a hole in the tube. In any case, I don’t know how much tread is left once the holes are worn down. It could be possible to safely ride your rear tire once the wear indicators are gone, but not for long. Under no circumstances would I do this on the front tire.

Come to think of it, on the forums I used to frequent, I would sometimes hear about riders wearing their tires down to the threads. That was a reference to the threads of the tire carcass. Many higher end clinchers and tubulars in the 2000s had cotton carcasses, which could be very supple. Presumably (NB, I’m not an engineer) this was supposed to reduce energy loss due to hysteresis, which is a primary driver of tire rolling resistance.

| improve this answer | |
  • 3
    Regarding your last paragraph, all the brake-compatible rims I've dealt with made in about the last 20 years have had a wear indicating groove, except one set on a BSO from about 2002. But most of these were touring/MTB/utility rims, only one set on an entry-level road bike – Chris H May 8 at 5:58
  • 2
    It really depends on the rims you work with. To me it seems that most mid tier rims have the wear indicator groove, but high and low end don't. For example Mavic catalog, MA3 / Open Elite has the wear indicator but Open Pro and complete wheels don't. – ojs May 8 at 8:15
  • @ojs you could well be right. I wouldn't call any of my stuff high-end, but my newer bikes both have disc brakes. The wheel I had built compatible with disc and rim brake definitely had grooves. – Chris H May 9 at 20:58
23

It’s an intentional wear indicator.

There should be “TWI” (Tread Wear Indicator) and a small arrow printed on the sidewall where the dimple is. When the dimple is no longer visible your tread is almost gone and it’s about time to replace the tire.

| improve this answer | |
  • There acutally is! Good catch, thanks. – Gistiv May 8 at 6:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.