Lower profile tire in the rear?

A friend just picked up a 2010 Mercedes C300 from a used car dealer. I noticed that her car has 225/45 r17 in the front (proper recommended size for the car), but 225/40 r17 in the rear. What kind of problems would creep up because of this? I think she should return to the dealer and have them put the recommended tires all the way around.

The tire size in the rear should be 245/40R17. What is shown on the tire information label in the door jam?

Is it the AWD version? Then there could be damage to the AWD system. If RWD, the difference might set off the traction control/ABS improperly. Time to get all 4 tires the same size.

Look again at the rear tires to see if you may have mis read the 245.

On many cars with different fron/rear, the objective is to have a wider rear, but not shorter ( closer to the ground )
If hers is the sport trim the fronts are in fact the 225/45r17 and the rears, like neveada said, are 245…245/40r17
IF hers actually has the 225 on the rear …it’s those that are wrong.
if hers has the luxury trim then all four should be the 225/45r17.
How to tell ?
The rim bead WIDTH…ie; how wide are the rims ? The type with the different rears truly has wider wheels back there with the fronts being slightly narrower.
The other has all four wheels the same , ergo, all four tires the same.

Great information, everyone. The best tip was to look at the information on the door pillar. (Thanks, Nevada-545). I’d never seen this before, but the front tires are supposed to be 225/45 and the rears are supposed to be 245/40. I misread the tire and thought both tires were 225s, but upon detailed inspection, they are correct. So I’ve made my friend stress out for no reason and I think I owe her a Coke. But we both learned something. Thanks, all!

Sounds like buying a new set of tires will involve shelling out some serious cash…But that’s one of the many joys of owning a Benz…

You were right to be concerned. Especially with newer cars with the high-tech suspension systems, it’s wise to stick with the exact tire size recommended by the manufacturer.