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?
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.
Here are some photos for reference. Below is a Continental Grand Prix 4000 near the end of its life; I think it had close to 5,000 miles as a rear tire. One of the two wear indicators was completely worn off. I electively changed it, because I was getting a number of punctures. (Albeit I had a few wet weather rides.)
This is a GP 5000 with 2-3,000 miles on it as a front tire. There is slight wear, and you can see both dimples. I rotated this tire to the rear after discarding the former rear tire.
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.
@A.Jahin asked a question where they posted a photo of a tire where the tread had been completely worn out in one spot due to emergency braking. This wore out the tread in one spot, and the threads of the carcass are visible and are abraded. This is roughly what it will look like if you are trying to wear the tire down to the carcass.
For reference, rim brake rims sometimes have wear indicators as well, usually a dimple or a groove. 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. This answer shows some examples of worn out alloy rims.
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.
