2005 XC90 2.5T: all tires need replacement when one is flat?

Post by **cn90** » 21 Oct 2014, 21:26

I understand this is an old topic but want to ask the AWD tire gurus around here...

I have tire issue with my 2005 XC90 2.5T with 85K miles.

- Goodyear Assurance tires with about 8K miles on them.

- Currently tread depth is 8/32 inches (vs new = 11/32 inches)

- LF tire has sidewall damage (hitting curb) and bulges slightly. This has to be replaced for safety reasons.

- Local Discount Tire shop told me that for 4x4 vehicles as long as the difference in tread depth is less than 4/32 inches, tires with small differences in tread depth can be used and the drive train is unlikely to be damaged.

- They recommend: the brand-new tire to the rear axle (so the REAR axle will have 11/32" and 8/32" tires), and move the "old" tires (with 8/32-inch depth) to the FRONT axles. Does this sound right?

Post by **jimmy57** » 21 Oct 2014, 22:13

Yes. Haldex AWD system is forgiving and your tire size range with that new tire is within its tolerance.
The research supports the best tires on rear for hydroplaning reduction on the axle you get the least feedback from and that also has the least direct of way of controlling if traction is lost.

Post by **cn90** » 22 Oct 2014, 06:49

Thanks jimmy!

Appreciate your expertise.

Post by **cn90** » 22 Oct 2014, 09:34

I am wondering my options (I have Haldex AOC system in my 2005 XC90):

a. Replace only 1 tire:
- FRONT axle: 8/32" and 8/32"
- REAR axle: 8/32" and 11/32" (one new tire)

b. Replace only 2 tires:
- FRONT axle: 11/32" and 11/32" (two new tires)
- REAR axle: 8/32" and 8/32"

Any suggestions?

Post by **jimmy57** » 22 Oct 2014, 13:24

Diff in either end will average the one tire replacement to be a very low value. Two tire replacement will make that a larger deviation and would turn AWD off once you get to 24 MPH or maybe less (I forget the critical speed, it is either 30KPH(18mph) or 40 kph(24mph).
Even when DEM signal dumps static clutch apply pressure you can still have a slow and reduced AWD engagement if wheel slip occurs.

Post by **jimmy57** » 22 Oct 2014, 13:26

Diff in either end will average the one tire replacement to be a very low value. Two tire replacement will make that a larger deviation and would turn AWD off once you get to 24 MPH or maybe less (I forget the critical speed, it is either 30KPH(18mph) or 40 kph(24mph).
Even when DEM signal dumps static clutch apply pressure you can still have a slow and reduced AWD engagement if wheel slip occurs.

One more option: one new tire and a shop that can shave tread. Not many doing that any more but it would be the least costly fix.

Post by **cn90** » 22 Oct 2014, 19:49

Per tire shop recommendation, I bought 1 brand-new tire (same brand and everything: Goodyear Assurance Fuelmax type):

---> FRONT axle: two "old" tires with 8/32" depth
---> REAR axle: 1 new tire 10/32" and 1 old tire 8/32".

Car drives fine.

The difference is 2/32" = 1.6mm, which I think is negligible for the REAR axle.

However, when I bought this vehicle (2005 XC90 2.5T AWD), I kind of had a plan B from reading forums: if and whenever the AWD takes a dump (bad transfer case, driveshaft, Haldex, AOC etc.) I was prepared to convert the vehicle to a FWD car.

So, having slightly mismatched tires in the REAR axle should be fine. In the worst-case scenario (which I think is very unlikely) of rear diff going banana, the car will be a FWD machine...lol.

Post by **SuperHerman** » 09 Jun 2015, 23:14

It is always best for all tires to be close in size. If only one new tire is required and the other 3 are fairly new you can always have the "new" tire shaved down to match the wear depth of the other tires. Granted you are throwing away good tread, but if you do not want to risk transmission problems, have the tire shaved to an appropriate depth. Not all shops can shave tires, but if you shop you shall find.