My wife had a blowout on one of the Pirelli STR's that came with our 2005 XC70.
We have about 15,000 miles on the car and maintained regular service.
I had a Goodyear Assurance ComforTred put on because that was the closest tire store at 5 PM and didn't want her to be driving on the temporary spare.
Now that I have time to research, I learned that it may not be wise to have one different tire with the AWD XC. Goodyear Revolutions per mile = 774, Pirelli Revolutions per mile = 770. And the Goodyear has significantly longer wear life, so eventually I'll have an even more oddball tire. Otherwise, very similar tires as sold new.
I've browsed Tirerack.com and will call the dealer today.
Questions:
1) Will I damage the Haldex AWD system with a tire that may be slightly different than the rest? (If yes - why does Volvo provide a temporary spare that is three quarters the size of other tires??)

2) Can I replace the one tire with a new Pirelli or is the difference in tire wear enough to cause damage?

3) Any advice on replacement set of tires would be appreciated. The Pirelli's seemed to work fine for us. I'm concerned about the blowout after reading more about the trouble some people have with the Pirelli's. I can live with the wear life if these are the best tire for the vehicle. But I have a hard time convincing myself that I need V speed rated tires. Considering Michelin's or Goodyear Tripletred.

Thanks in advance.

I may have found the answer to my questions at 4x4abc.com.

Quoted from the website: "Please note, that newer Volvos with Haldex couplings do not suffer damage when the tire sizes are slightly unequal."

I would still like to learn if anyone has heard about this issue.

Performance issues aside, ideally you should replace all the tires in the same axle. Tires have different wet handling characteristics, rubber compound, etc which may cause the car to drift or veer to the side when brakes are applied suddenly. Some argue that even if the new tire was the same, both should be replaced (preferably with the same manufactured date) because the older tire would have had some wear and the rubber compound would have changed.

As poopbunny said, you want the same traction capabilities, especially in winter driving.

Hmmm. Ran into this problem with my 2000 V70r AWD. One expensive possibility is that you may need to replace your angle gear because of the difference in circumference in your tires. My bill would have been $2200.00 had I not had an extended warranty. The dealer was unsure of the solution to the problem, but the technical guy from Volvo diagnosed it as different circumferences.

Honestly, I don't know how it happened or whether he was blowing smoke. I rotate my tires every 5k and have a separate set of wheels and tires for winter and summer. I probably drive 20k (10 in winter and 10 in summer).

If you drive a lot in the snow in winter, consider a set of Michelin Arctic Alpin tires. Phenomenal grip and quite good wear. The Tire Rack did not stear me wrong on these tires.
Clay