Re: 1991 ranger brake problem

On 13/11/2024 22:09, Snag wrote:

   I thought it was exposure to sunlight/UV that caused most of the sidewall degradation ... or are those aftermarket tire covers (in particular for RV's and campers) just another scam ?

It's usually the UV which does the damage, though ozone cracking can also occur. Mostly tyres rely only on the carbon black for UV protection - I don't know of any other anti-UV additives which are widely used in tyres. Better tyres may however contain (more or better) antiozonants (yes, a real word, and thing).
I haven't come across aftermarket tire covers, but if a tyre is going to be exposed outside for long periods, like RVs and campers, on a first look just to prevent UV exposure they would make sense. They might also slow exposure to ozone by providing a physical boundary, or be lined with something which is more reactive with ozone than tyres - likely, as ozone reacts with most plastics and fibers.
Tyres are made to last for 5 to 7 years, because on a normal car they would need replacing due to wear after this time. However a RV or camper might not need type replacement due to wear for decades, so protection from UV and ozone could save a lot of money.
Whitewall tyres were originally made using zinc oxide as pigment, but they use titanium dioxide nowadays. White rubber is more susceptible to UV than black, because the lampblack or carbon black which makes tyres black also helps protect the rubber against UV.
The carbon black does several other things. It decreases susceptibility to attack by oxygen, increases the thermal conductivity - important to prevent parts of the tyre from getting too hot -, strengthens the vulcanisation, increases the tensile strength of the rubber, and increases abrasion resistance. Whew, good stuff!
Peter Fairbrother