I need new wheels (2006 xc70.) found a set, the offset is 40+. Most, if all aftermarket seem to be in that range. Volvo specs say 47-50. Also....width? 7, 7.5, 8? Will it matter? Darn... What happens when one uses wheels with lesser offset, etc?

Wheel offset begins at the center of the wheel plus or minus tells you either the wheel has the center of the rim mounted inside or outside this center.

If the offset is wrong by enough, the wheels will either be too close to the inside of the car and rub on the suspension, or too far from the inside of the car and rub on the fenders.

OK...Help me with my choices. Strictly by the #'s. I have plugged in the info to Tire Rack- 2006 OR 17". I'm still trying to understand offset, etc. I searched for Volvo wheels, but the two sets that I looked into were painted poorly and one was welded over a crack. I feel better buying new.
Here are the options:

Sport Tuning T-15 +42mm, 17x8
Enkei Performance J-10 +38 17x7
Sparko DRS +45 17x7.5
Platinum Prophecy +40 17x8
Voxx Vento +40 17x 7.5

You should be careful when using wider wheels.

What does an offset of 40+ mean? The offset is a specific number of millimeters.

you can find info on the internet on how to measure offset. The hard part is having a straight edge of the proper length to span the wheel edges if there are tires mounted on the wheels.

Wheels that are too wide may rub on something. On our 744 turbo, the hydra wheels that came with the car rubbed on the wire to the antilock sensor on one of the front wheels until the wire was worn to its center. On our '96 855R, the wheels were so wide that the car had special front fender liners that were cut away near the shock towers so that the tires would not rub.

Volvo actually built the car with wheels were too wide for the car without special parts! If you put those wheels on a regular 850, the wheels would rub all the time!

Also be aware that wide tires are much more sensitive to tire pressures. If your wheel or tires have a slow leak, the problem gets serious more quickly.