Volvo has a TSB that explains the AWD limitations. It is:

4460005 01/01/01 Wheels/Tires - AWD Information & Function Test

Some info from it (can't post it all since it has diagrams, etc. but
the dealer can pull it for you):


Note! To prevent deterioration in the function of the power transmission system on All-wheel drive (AWD) cars, it is important to follow the instructions below.

All Wheel Drive vehicles have special requirements for tires and wheels. It is very important that the tire replacement guidelines below are followed. Failure to do so can result in damage to the AWD components (angle gear, viscous coupling/freewheel unit).

Always drive on tires of identical brand, size, construction (radial), tread pattern, load-, speed-, traction-, temperature-, and treadwear rating.

Never drive on mixed tires, except for brief periods when the temporary spare tire is in use.

Always use properly inflated tires of correct dimensions. Tire size and inflation pressures are shown on the tire pressure label located inside the fuel filler door.

Caution! Failure to always drive on properly inflated, identical tires of correct dimensions may result in a circumference difference between tires on the front and rear axles. This will cause excessive tire wear and may damage the transmission and all wheel drive system.

Replacing the tires

When tire replacement is necessary, Volvo strongly recommends replacing all four tires at the same time with identical tires as explained above. Failure to do so can result in circumference differences that may damage the transmission and all wheel drive system.

If only one or two tires are replaced, the new tire(s) must be identical to the tires with which the car was built, and must be mounted on the FRONT AXLE ONLY! Failure to do this may damage the transmission and all wheel drive system.

Spare wheel Temporary spare

The temporary spare tire is for temporary, low-speed, short-distance use only Do not drive on the temporary spare at speeds above 50 mph (80km/h) or for distances greater than 50 miles (80 km) or transmission and all wheel drive system damage may result.

Snow chains all-wheel drive (AWD)

On all-wheel drive cars, (AWD), snow chains must only be mounted on the front wheels. Only snow chains intended for all-wheel drive (AWD) cars can be used. Never install snow chains on a temporary spare tire.