Replacing Damaged Tire on AWD XC70

[vooman82]

I have a 2004 XC70 and have a damaged tire. This is my first AWD vehicle and I have read that there are issues with making sure all tires are matched. I bought the car used and the spare is not the same manufacturer and type of tire that are on the rest of the car. I have not been able to find what the requirements are for a Volvo XC70, when it comes to matching/replacing tires. Does anyone have any information on this? How closely, does the tread depth have to match to avoid causing problems with the AWD? Can I match the tires in pairs, front and back or do all 4 tires have to be matched? Thanks,

[draser]

Not having an AWD I don't have direct experience, but I don't believe that all 4 have to be matched (as far as wear). If you don't have active chassis control - like the R version - there are no height sensors to trip. The diameter difference (which is like 1/8" to 1/4" = not significant) may influence the number of pulses that the wheel sensor sends out, however the antilock system - that works in conjunction with your AWD - does not count pulses but checks for their presence within a timeframe (on the low end when losing traction). As far as the torque differential between a new/used tire it should be negligible for any sensor to detect - if that weren't true you'd get all kinds of traction faults while driving on a road that has wet spots, sand, etc. So there's a safety range baked in there that allows for some torque differential.
Any other opinions?

[jimmy57]

The Haldex based system that car has is not hypersensitive like the viscous system but it still matters that they be within an inch in circumference.
There is a little torque transfer when the system is rolling down the road and too much speed difference is going to get the angle gear warmer and wear the haldex unit clutches.

[vooman82]

Thanks, for that info. I will check the wear on the remaining tires.