chkMINUS

Bought a used '09 C300 a month ago.

It has brand new front tires.
Michelin 225/45r17 - Pilot sport a/s 3

Drivers rear is bald
Continental 245/40 r17 - Contiprocontact

Passengers Rear is in good shape
Pirelli 245/40 r 17 - Pzero nero


I'm replacing the back bald one asap. Do I want to leave the new Michelin's on the front? Are these directional tires/ do I rotate them? Best idea to get a matching Pirelli 245/40 r 17 - Pzero Nero? Thanks.

shotgun_banjo

Get matching tires (I mean match the front tires). Some people will say it is fine having 2 different tire brands but you have no idea what the car will do when you do emergency maneuvers. On the track people sometimes literally put different tire brands to make their car behave a specific way but for everyday use I think it is best to have them all the same.

edgalang

Personally I'd leave the front Pilot sport a/s 3's alone and get matching Pilot sport a/s 3 for the rear.

The AS3s are pretty good tires.

Atlas Grey

Minus,
First off you need to check the thread depth of your other tire. Any more than 2/32" difference may give you problems so unless your passenger rear tire is almost new you really should not just replace the one tire. Second as the two others have said the tires should match if possible. The tire compound, tread pattern etc all work together to create a stable, comfortable and quiet ride. Missmatching tires is not recommended if it can be avoided. The Michelins you have up front are a very aggressive compound that is great for aggressive driving. If you end up using a different possibly harder compound all season tire you may have instability in handling in cold or wet weather conditions and you will almost certainly have issues with oversteer with a harder compound on the rear in any type of aggressive handling situation. This is not something that you want and when it happens it is fast and there is nothing you will be able to do about it.

I work for a tire and service company and we install 4 million yes 4 million tires a year on customer's cars. Take your car in to a tire shop that carries Michelin tires. Have them check the tread depth on your passenger rear. If it's below 2/32" replace them both with the same Michelins you have up front. They are not inexpensive tires but are really a great premium quality tire and worth the extra $

chkMINUS

Yes sir! Good Advice! I'll be replacing the rear with the same Michelin's. I noticed the size difference between front and back. That's standard right? Am I supposed to rotate/swap the fronts with each other and the backs with each other at intervals?

myn8m3is8ndy

I recently got a flat on my rear passenger tire. Nail went straight into the sidewall. According to the shop who warranty my tire, they said i had 6/32 left. I opted to replace just that 1 tire. So according to their information, I have 6/32 of my rear driver and about 10/32 on my rear passenger. I asked about shaving the tire, they said that dont do that.
So my question is, what kind of problems are you talking about?

Atlas Grey

If you have a sport model of your car you almost certainly have what are referred to as Staggered Fitment. The fronts are smaller than the rear even though the Wheels themselves may be the same size. What I am saying is your Front Wheel could be 18 X 7" and your rear wheel 18 X 8.5". Clearly you would have wider tires on a wider wheel. My wifes c300 sport I believe runs 225 up front and 245 in the rears I think my C350 is 235 up front and 265 rears.

You cannot rotate these tires front to back and depending on your tires you may not be able to rotate them side to side. Look at your tire sidewall. If there is an arrow with the words DIRECTION typed in the arrow or around the arrow that means they are Directional tires so only a right front 225 tire would be on the right front. My old 911 has directional tires that are staggered so I wear through a set of tires very quickly as I can't rotate them. Hope that makes sense.

BTW some luxury MB models do not have staggered fitment. All cars have a tire placard on the driver's side door that says exactly what your car came with. Make sure you know what you have stock and then buy those as a replacement. If you have a luxury model and they are not rotational tires you should rotate the tires front to back etc.

We always put the newest tires in the rear of the car regardless if it's front/awd or RWD. That can't happen with staggered fitment obviously.
Tire rotations where possible should be done when you change your oil as a good rule of thumb.

Atlas Grey

The reason we typically don't want to put two tires with more than a 2/32" difference is due to the differential having to work harder. Think of it this way your tire's circumference is slightly different for each tire on the same axle. The more used tire rotates at a faster speed than the other tire which long term can cause issues with the differential.

In vehicles equipped with all-wheel drive (AWD) systems, the transfer case (gears that transfer power from the transmission to both the front and rear axles) and the car’s internal computer work together to send power out to each wheel. The amount of power-per-wheel can vary, depending on each wheel’s individual work load. For example, in a straight line each wheel carries a reasonably similar load. In a cornering situation the stress on each wheel is very different.

So the amount of power the internal computer sends to each wheel – based on what your AWD vehicle needs to go down the road – helps to manage how hard the transmission and transfer case are working.

With inconsistent outside diameters caused by different tire sizes, tread patterns or tread depths an AWD computer’s readings will fluctuate. Various wheels will receive inefficient or incorrect power loads. As a result the drivetrain (computer, transmission and transfer case) must constantly readjust, doing more work than necessary and eventually, may break down.


Hope that all makes sense
Caesar