New tire matched with old tire: issue or no issue?
Stelvio Quadrifoglio with 10,000mi. I got a screw in the center tread of rear tire. Have road hazard insurance. Vehicle in for 10,000mi service at dealer. I ask dealer to sort out the tire. I figure they will just patch it (center tread). Dealer calls back: "good news, hazard insurance giving you a new tire." (These are 285/40R20 Pirelli P Zero). "I say OK, what's the other tire look like?" My understanding (cell phone reception) is other tire has 6/32 wear (6/32 remaining). Half tread left, but guessing another 5000mi +/- on it. This puts the old tire 3/8" smaller in diameter than the new tire, 1.2" smaller in circumference. New tire dia. 29", circ. 91".
So my question is: Is this amount of tire size difference problematic?
From what I've read in various auto blogs, rule of thumb is to replace the tires in pairs, but if less than 2% difference, not a problem. (About 1.3% diff). But it's a little confusion on the topic as some people answer this type question as understanding you have two slightly different tires on the same axle and others weigh in opinions on whether you simple have slightly different tires between the axles. (Which is the case in the Stelvio any way as the front and rear tires are different sizes to begin with). And other blogs, people are weighing in on deviating from manufactures supplied tire size. So sometimes the answers are confusing if you don't understand the assumptions of the commentor.
FYI: dealer quote for new tire mounted, $550.