OK - I've searched this forum and read and re-read my Owner's Manual looking for a definitive anwser on the restriction for replacing a single tire on the R wrt tire tread depth differential.<p>I found one posting from JRL that says the differential should not exceed 3/32", and if it does then replace all 4 tires.<p>My situation is this. My front passenger side P-Zero (stock tire) tire has developed a bubble/blister of approx 1.25" dia. All four tires have 15,000 miles on them and the wear bar has not been reached on any. The LF/RF both have about 6/32" remaining and the LR/RR have 5/32" remaining. Tires have been rotated front-to-back per Volvo's recommendation every 5000 miles.<p>So I have to replace the RF tire. A new tire has a tread depth of 10/32" to 11/32" (is this correct?). Thus this new tire will mean a tread depth differential of around 4/32" to 5/32" between it and the other three tires.<p>So, should I replace all 4 tires or can I safely replace just the RF tire? The cost difference is substantial at around $800.<p>I'm apt to want to replace all 4 tires but don't want to if it's not really necessary. I know I'll have to replace all four tires before next winter and wonder if tire prices vary such that they are cheaper in summer vs. winter time or at least with the onset of winter.<p>Thanks for any advice.