I have a set of Mercedes OEM double 10-spoke wheels.

Front: 18x8.5 et38
Rear: 18x9 et39

Instead of putting 245/40/18 front and 265/35/18 rear. Can I put 245/40/18 all around? I have a E350 4matic.

 

You would be stretching the 245s in the rear, while they are perfect for a 8.5 in the front 9 is too wide. The range for a 9 inch wide wheel is about 265 to 285 but it all depends on the manufacturer. If you want to go square all around get a matching set of 8.5s for the back or a new set of wheels.

My concern is that you are driving a 4-Matic. I suggest you search the forum as I actually asked about a staggered setup on 4-Matic a while back and got some very good technical answers. The short explanation is that while yes you can run staggered, you need to be within 1/10th of an inch (I think) of rolling diameters between wheels and tires front to back. However, I've also been told that it will affect handling a bit on rougher roads and therefore isn't the best idea. You could probably do that staggered setup but my recommendation is to get 8.5s all around then run square 245s

 

Actually found that discussion https://mbworld.org/forums/e-class-w...ml#post5276601

 

I understand putting 18x8.5 on all four corners would be ideal, but I couldn’t find them. I am not an expert, but I think they should work from reading online.

According to information found on Tirerack, 245/40/18 can be mounted on 8-9.5” wheels. Reading the following Tirerack article. I understand that the tire contact patch might be approximately 2/10” different, but the diameter of the tires would be very close (if not the same).

“The width of the rim will influence the width of the tire. A tire mounted on a narrow rim would be "narrower" than if the same size tire was mounted on a wide rim. NOTE: Because the overall diameter of a steel-belted radial is essentially determined by the steel belts, there is little, if any, change to the overall diameter of the tire due to differences in rim width.”

http://www.tirerack.com/tires/tirete...jsp?techid=198

 

Answer from Tirerack, "You can run the 245/40R18 all the way around, but that sort of defeats the purpose of having the staggered wheels. What I would suggest looking at would be the 245/40R18 and 275/35R18 for the rear. That will keep the overall diameter of 25.7" fronts and rear so it would not affect the all-wheel drive system."

 

I don't think you understand what I am getting at. Yes you can run 245s all around on 8.5 front and 9 rear. But you will be stretching the sidewalls on the rear wheels to the point where they start to look ridiculous and could compromise safety - yes it can be done but it's not a very informed decision.

Yes you can run staggered width wheels on a 4-Matic, but for my reasons stated above the car is not tuned to run them. So you may actually end up inducing more understeer or have worse handling especially on rough roads - who knows, I've never done this before and not many people have for that reason.

Either get a new proper set of wheels, or run a staggered setup and just BE CAREFUL as Tirerack said. They may be good with wheels and tires but I'm absolutely sure they are not experts when it comes to the handling characteristics of a W211 when fitted with non specification width tires. You own a Mercedes, either spend the money to do it right or don't do it at all.