I'm looking at a used CPO GS 350 AWD. I've always been told that its bad to use tires of different tread depth on all wheel drive cars as the difference in diameter is bad for the differential. However, this particular GS was equipped with standard tires and a compact spare - I would think that if different tread depths make a difference, then use of a compact spare would be even more detrimental to the car. Can anyone confirm that compact spare usage is OK?

 

Compact spares are meant as temporary solutions to get you to a shop to get your tire repaired/replaced. Driving a few miles on a donut isn't going to destroy anything. You're definitely not supposed to go finish the rest of your cross country road trip on the donut.

 

BinaryJay is correct.

Additionally, some GS350s have runflat tires which (like the donut) should provide you with a way to drive a minimal amount of miles in order to get a repair/replacement.

 

yup, BinaryJay hit it. it's only meant for temp driving, just a few miles to get your tire fixed

 

The problem is not thread depth, but an overall diameter of the tire. So the spare is closely matched to the diameter of our stock sized wheels - enough so you can drive a few miles to the shop

 

How about those emergency tire repair kits - the ones where you squit a compound into the tire that plugs the hole (like this - http://www.amazon.com/Slime-70005-Sa...3744139&sr=1-3), would that screw something up, particularily the pressure sensors?

 

Yeah it will mess up TPMS. The way it works is the tire is full of air and you inject this "goo" that goes all around the tire looking for the "hole" to patch. Well the goo goes everywhere searching for it. I've seen tires unmounted with it and its a mess.

If you don't have a TPMS, these fix a flat systems work great. As a matter of fact BMW and I think a couple other brands put them in their cars instead of a spare (for some models)