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Summer tires front, all season rear, dangerous?

I have a 2004 CLK320 coupe with sport package, 245/40/17 91Y rear, 225/45/17 91Y front that I bought ~6 months ago. All 4 were Continental ContiSportContact2 (a summer tire). Now the rear tires are worn out but the front have more than 3/4 of tread left. The dealer said to put 2 new SportContact tires on the rear. However, after some research on tirerack and similar, and not wanting to have 2 sets of tires (winter and summer), I chose a pair of Michelin Pilot Sport A/S 245/40/17 91Y for the rear, exactly the same specs as the existing ones except for 2 parameters:

a) tread pattern is very different (all season)

b) wear time is longer (400 vs 200)

I had them installed at a local tire center and after they put them on, they said, check with the dealer to be sure that you don’t have to change the front ones also to the same tread. So now I am concerned.

Since longer wear time = less “stickyness”, even though the rear ones are new and the front ones are older, could it be that because the front are summer tires they will have more traction than the rear and this situation be dangerous in an emergency? Or will the fact that the rear are newer mean more traction in rear and I am ok? I would hate to have to buy another front set when they are perfectly fine now.

Tough question, the handling will certainly be a bit different, but having stock tire sizes, both pairs radials, should lessen the potential for dangerous handling. Anywhere you can test it out (parking lot, that kind of thing)?

I think it’ll be fine-- you’ve got the better tires on the back so you shouldn’t have too much trouble keeping the car under control in an emergency. I might not want to drive it like this in a snowy winter, but you shouldn’t have the summer tires on anyways.

I have a feeling the rear tires WILL have less traction than the fronts, as you suspect. This is a recipe for oversteer, especially since this vehicle is by nature (with OE tires) a fairly well-balanced handler. How much of a problem this will be remains to be seen, but I wouldn’t risk it. A quick trip into the weeds on a high speed turn isn’t pretty.

You have a premium car that unfortunately requires premium treatment. Replace the front tires with ones to match the rears.

Now the rear tires are worn out but the front have more than 3/4 of tread left.

This is a sure sign you didn’t rotate the tires in a timely manner. All four of your tires should wear out in a relatively uniform fashion. I hope you learned your lesson for future reference.

I agree with NYBo. On a car this expensive, spring for the other two tires so the front tires match the rear tires, and then get them rotated each time you get an oil change to keep this from happening again.

He can’t rotate, they’re different sizes front to back. Another disadvantage of the high-performance cars with “sport packages”…

Not many people rotate tires anymore anyhow. two different tire sizes, plus directional tires = no rotation possible unless you want to unmount and remount from the rim on the other side.

Even directional tires can be rotated, even if they can’t be rotated to the opposite side. With same-sized directional tires, you just swap the front and rear wheels.

The sportcontact are not directional, but the car has different size front to back so they can’t be swapped. Both front are evenly worn much less than rear. Not sure if that is just because the rear really wears out that much faster or the previous owner only changed the front at some prior point in time.

Thanks for the thoughts, replacing the front ones for the winter even if they are not fully worn sounds like a reasonable scenario.

Too many burnouts, maybe?