The main causes of tyre cracking are attack by ozone from the atmosphere, lack of use and strain and overheating, particularly from under inflation
and UV as mentioned. Tyre compounds contain carbon black (C) which is basically incompletely burnt oil soot. The C molecules are added to stabilise the rubber, transfer heat and reduce rolling resistance and is what makes tyres black. When a tyre is used the molecules in the compound are agitated maintaining the chemical bonds helping to resist cracking. When tyres are not used for a while Ozone attacks the surface of the tyre loosening the molecular bonds in the material, but cracks will not form until the tyre is subjected to stress and strain. So an old tyre that hasn't been used for a while can look fine but will suddenly develop cracks when used again. The cracks develop at the surface where the Ozone has been at work but are not actually a safety issue unless the ply is exposed or the tread is in danger of separating, which is a biggie on our cars and would be the main concern.
I had a perfect example of this when I bought a 14 month old car that had been driven for 300 miles and garaged. The tyres were obviously as new, but within a few months started cracking horribly and had to be changed. This is why buying old tyre stock may be a false economy and I always ask for tyre dates when buying
In a previous life I helped design parts of the old Sevalco carbon black plant near Bristol which supplied C to many makers around Europe. Different makers are now using various additives and formulations of C to improve performance and some will resist cracking better than others, but there is little you can do to prevent cracking other than using the tyre and keeping it properly inflated
. Six years is the industry standard for tyre life although I've had tyres way older than that that have been fine, I've also had tyres with micro surface cracks that never got much worse and were used until worn out.
Interestingly solvents, detergents and other chemicals found in some 'detailing' products may actually degrade the chemical composition of the tyre surface, you would need to check out the exact formulations and do a bit of research but my guess is a lot of them will make tyres look nice but do more harm than good in the long run. I open the floor for informed debate on that one......
2003 2.5 SE, low miles, Sterling Grey, 108's & Eagles, no stubby here! Unmolested.
2018 Cooper S Countryman