What is the recommended PSI on 225/40 18" tires?

 

I would start out with 30 front and 28 rear if you are the only one in it. The more load you add the more you'll need to adjust. To get it correct for your use drive the tires thru a puddle of water and then look at the tread spacing and compare it to the tires. Make sure the spacing is the even from one to another and you should be good to go in terms of mileage and traction.

 

That is the funniest technical data acquisition method I have ever heard of, LOL. Ironically it'll work to give you a decent idea. If you drive hard, the scuf marks on the shoulders will also indicate if you are too low.

But the best thing to do is measure tread wear on the left, middle and right of each tire. Take the readings write them down. If the centers are wearing, your PSI is too high, if the outside is wearing faster, you are too low. It is also a good way to watch your allignment. Tire selection, driving style, and roads may also have an impact on what will work best for street driving.

 

I personally would run higher than 30-28 with that setup. For one thing, MB's recommended pressures are higher in back than front. So I raise these pressures, but usually keep the back higher than the front. With my C7's, I set mine to 35 front and 38 rear about 3 weeks ago. Temps were mild that day, so on some warmer days, I am probably running a few more psi than that. But I find that the car handles quite well with these pressures.

 

I would never go below 33psi on either axle with 18" wheels. The sidewall is too short to risk your [expensive] rims, especially after the past winter, which left enormous number of potholes on the roads. I prefer firm and controllable ride, and my settings (stock C7 17" Mich Pilot Sport) are 38 rear /33 front.

 

On every Benz Ive driven and had, the front tires always would wear out on the edges. I counter acted this by always putting the front a few pounds more. This does increase understeer in wet weather tho.

But my tires now wear evenly, my clk, the coupe and the old S class we had all wore out the front edges prematurely at the manufacture reccomended pressures. None of the cars were lowered.

When you drop the front, you get more negative camber and this definately makes the tire wear less on that edge.

I drive rough tho, so that could be why I eat edges of tires.

 

I think you're right. 33 - 35 would be dangerously low for the 18"

I do the inverse here though, C7 wheels and S-03's, I run 36F and 34 rear.

Vadim, have your centers on the rears been wearing faster?

 

I never measured the tread wear, but they seem to be wearing fairly evenly across. That said, I drive mostly highway/city, almost no twisties and no track.

 

I got 7 k to the rear conti's from the C7 package. I constantly ran 35 psi in the rear, and this was obviously too much because the centers were definatly worn more than the outer by far.

My fronts are always run at 38 and there is great even wear, I know for next time not to run so high in the rear tho, maybe the overinflation causes the esp to come on when I accelerate hard?

Im talkin whenever I take a corner and punch it they would come loose, my new tires dont have this problem. They are cheap ones too, there called Nankang's.

Only ran me 78 bucks each A rated traction and temp, and 340 treadwear. It looks like a copy of the P7000 Pirelli, but I am definately more satisfied with the wear and grip with these over the stock continentals. I even got 2 bubbles in the sidewalls' of the stock conti's probably from hitting potholes, but the sidewalls are only 1 ply not even reinforced to begin with

Live and learn.