the question is: how much “older” would the tires without covers or with black covers be than tires that were covered with white covers?
tire a has a cover. so lets figure that as our control so there are 25 days times 6 months times 8 hours per day of solar heat exposure for a total of 1200 hours.
tire b has no cover, so it’s temperature is two times 18° hotter. remember the “aging” rate doubles (times 2) with each 18° increase so this tire spends 25 days times 6 months times 8 hours times 2 times 2 or 4,800 hours.
the difference is 3,600 hours which equals 150 days or almost 