Originally Posted by allgoo19
I used to buy tires showing cracks on the rubber(nothing wrong with the functionality) as soon as I put them on the wheel. I thought that was pretty norm, but lately, the tires I put on the wheel have no cracks. Is this because the change of rubber compound? Or I was just buying old outdated tires before? Newest tire I bought specifically saying silica compound. Is it the one helping from cracking?
Rubber, whether it is synthetic or natural, is an organic compound that is susceptible to oxidation. It's just like rust on steel. In some environments, ozone, produced by photocatalysis of nitrogen oxides from cars
will attack rubber compounds very aggressively. (Think of ozone as a super oxidizer.) This leads to "checking" or decay of the polymer that is used to make the tires. Here in Colorado the problem is particularly acute.
If the tire has been sitting on a shelf for a long period of time, especially in heat or sunlight, it can decay without any help at all. Don't worry since the checking problem is only on the surface although over a preiod of years it can go much deeper.
The silica compound that is added hardens the rubber and is added to help keep the oxidation down but it also helps make the tires have less rolling resistance. You can go
here for an ubertechnical explaination and a confusing graph. Since bicycles, especially road bikes have such thin tires with a small amount of rubber on them, silica will increase their durability as well.
Stuart Black