I had the bad luck of having a flat on my 98 V70 AWD. This is the model
with the viscous coupling that can be damaged by mismatches in tire
diameter.

I am using 205/55/16 Michelin MXV4s, and have taken the following
action so far:

i) the flat (passenger front) was replaced with the exact same tire,
brand new, having 10/32" of tread depth.
the driver's front was at 13/64" of tread depth, and the two rear tires
at 7/32" of tread depth.

ii) I have rotated the two rear tires up front, so that both passenger
front and driver's front are at 7/32", and rotated the two front tires
back so the rear driver's tire is 13/64" and rear passenger's 10/32".
All tires are inflated to the same PSI.

To summarize the tire diameters:
driver's front 7/32" (formerly driver's rear)
passenger's front 7/32" (formerly passenger's rear)
driver's rear 13/64" (formerly driver's front)
passenger's rear 10/32" (new tire).

I understand that the system is very sensitive to differences in tire
diameter and asking the dealer, they indicated that the tolerance is
within 3/32" of wear. My concern is that the new tire, at 10/32" is
7/64" larger than the smallest tire (13/64"), which is 1/64" (0.5/32")
over the recommended tolerance.

Do you think that the difference in diameter is severe enough to damage
the viscous coupling in the car?

What would your recommended tire placement be based on the diameters
listed?

Thank you for your help.

"theo.chan@gmail.com" wrote:
>
> I had the bad luck of having a flat on my 98 V70 AWD. This is the model
> with the viscous coupling that can be damaged by mismatches in tire
> diameter.
>
> I am using 205/55/16 Michelin MXV4s, and have taken the following
> action so far:
>
> i) the flat (passenger front) was replaced with the exact same tire,
> brand new, having 10/32" of tread depth.
> the driver's front was at 13/64" of tread depth, and the two rear tires
> at 7/32" of tread depth.
>
> ii) I have rotated the two rear tires up front, so that both passenger
> front and driver's front are at 7/32", and rotated the two front tires
> back so the rear driver's tire is 13/64" and rear passenger's 10/32".
> All tires are inflated to the same PSI.
>
> To summarize the tire diameters:
> driver's front 7/32" (formerly driver's rear)
> passenger's front 7/32" (formerly passenger's rear)
> driver's rear 13/64" (formerly driver's front)
> passenger's rear 10/32" (new tire).
>
> I understand that the system is very sensitive to differences in tire
> diameter and asking the dealer, they indicated that the tolerance is
> within 3/32" of wear. My concern is that the new tire, at 10/32" is
> 7/64" larger than the smallest tire (13/64"), which is 1/64" (0.5/32")
> over the recommended tolerance.
>
> Do you think that the difference in diameter is severe enough to damage
> the viscous coupling in the car?
>
> What would your recommended tire placement be based on the diameters
> listed?
>
> Thank you for your help.

This seems to be too great a difference. Also, the larger tires should
be on the front. Try to find a shop that specializes in high
performance tires, they'll have the equipment to shave down your new
tire.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

Mike F wrote:

>"theo.chan@gmail.com" wrote:
>
>
>>I had the bad luck of having a flat on my 98 V70 AWD. This is the model
>>with the viscous coupling that can be damaged by mismatches in tire
>>diameter.
>>
>>I am using 205/55/16 Michelin MXV4s, and have taken the following
>>action so far:
>>
>>i) the flat (passenger front) was replaced with the exact same tire,
>>brand new, having 10/32" of tread depth.
>>the driver's front was at 13/64" of tread depth, and the two rear tires
>>at 7/32" of tread depth.
>>
>>ii) I have rotated the two rear tires up front, so that both passenger
>>front and driver's front are at 7/32", and rotated the two front tires
>>back so the rear driver's tire is 13/64" and rear passenger's 10/32".
>>All tires are inflated to the same PSI.
>>
>>To summarize the tire diameters:
>>driver's front 7/32" (formerly driver's rear)
>>passenger's front 7/32" (formerly passenger's rear)
>>driver's rear 13/64" (formerly driver's front)
>>passenger's rear 10/32" (new tire).
>>
>>I understand that the system is very sensitive to differences in tire
>>diameter and asking the dealer, they indicated that the tolerance is
>>within 3/32" of wear. My concern is that the new tire, at 10/32" is
>>7/64" larger than the smallest tire (13/64"), which is 1/64" (0.5/32")
>>over the recommended tolerance.
>>
>>Do you think that the difference in diameter is severe enough to damage
>>the viscous coupling in the car?
>>
>>What would your recommended tire placement be based on the diameters
>>listed?
>>
>>Thank you for your help.
>>
>>
>
>This seems to be too great a difference. Also, the larger tires should
>be on the front. Try to find a shop that specializes in high
>performance tires, they'll have the equipment to shave down your new
>tire.
>
>
from a recent posting here:

>Capta1n wrote:
>
>
>>>
>>> My son was driving his 1999 V70 XC & noticed smoke coming from rear of car.
>>> Pulled over and lifted hear and saw small flame and doused with water-put
>>> it out. Car would start but would not move. Car came to normal start and
>>> accelerated fine prior to stopping. Tow truck arrived and front axle would
>>> not turn. Dealership reported axial gear needs to be replaced($2,980) &
>>> then see if transmission affected. Aware of recalls or tech bulletins
>>> about this? Diagnosis sound reasonable?
>>
>>
>
>This is commonly called the angle gear. This takes power to the
>driveshaft for the rear wheels. It is the most (by far) common failure
>in the early AWD system. Usually, a tire size difference is to blame -
>the different axle speeds front and rear cause the viscous coupling to
>start to lock up. This causes driveline windup which stresses all the
>driveline parts. The weak link is the oil in the angle gear, which
>overheats. This can cause fires and/or angle gear failure. There are
>many tech bulletins about this.
>
twice i've had a tire go out and had to buy a new one. i got a fierce
lecture from a service writer when i had replaced only two (the bad plus
its mate) that i needed to replace all four. i don't know how close the
rules really are but the email above puts the fear in me. a whole new
set of tires was 4500 or so and a lot less than $2980 or more!

besides 7/32 is about 60% or more worn. buy three more and ask for the
set price!