My
opinion...not based on any scientific fact/research...
I think a lot of this depends on how the tires are used/stored. ANY tire that is subjected to the weather/ultraviolet rays is gonna deteriorate quickly, compared to tires that rarely get out of the shade. Sitting in one spot for long periods also contributes. High speed runs when cold effect them. Under/over inflation, products such as tire dressings/shiny stuff, grease-oil-brake fluid....you name it, it ALL contributes to the aging of the rubber.
I don't like buying tires...I also don't like blow-outs @ 70mph.
A good quality tire will obviously last/wear better than the "4 for $100" deal at Pep-Gurls.
The tire on the '74 have been on it since 1997...I put them on meself. They've got
maybe 5000 miles on them, and the car is always in the garage, and covered, with the exception of the few times it's been on road trips, or at local shows. The tires are still "new", treadwise, and have no sidewall cracking, or any other indication of deterioration. So I trust them to make a long road trip now? You betcha. That's just me.
The tires on the '85, however, are different...it sits outside all year, and even tho it is covered, the tires do get weather. I've replaced the '85 tires 3 times since I've had it, and I bought it in '98.
Don't take risks with your tires...if you have to ask "Are they still good?", then they prolly ain't...
______________
Joel Adams
C3VR Lifetime Member #56
My Link
(click for Texas-sized view!) NCRS
"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"