JimPap

I picked up my C300 Sport this past Friday and drove it home from the dealership approximately 90 miles away.

I know that a sports version should ride stiffer than a luxury car, but I really felt that it was too stiff.

Checking the cold tire tire pressure, I see that the front 225/45/R17s are at 33 psi, where the sticker says that they should be at 28psi. Rear tires 245/40/R17 were 32 and 33 with the sticker show 33.

Question, what air pressure do people generally run these tires at?

Edit: I adjusted the tire pressure on the front tires from 33 to the 28 that's on the sticker and the ride improved significantly. Now the question would have to be is that where I should leave it.

RLE

<<I adjusted the tire pressure on the front tires from 33 to the 28 that's on the sticker and the ride improved significantly. Now the question would have to be is that where I should leave it.>>

Yes.

JimPap

I can't help but question why the dealer or someone else upstream would have overinflated those front tires by 5 lbs.

Wonder if it has to do with the longevity of the tires or if they figure some nut (that be me) might push it over 100mph. The sticker on the gas filler cover does say to over inflate by 5 lbs if you're going over 100mph. But then, the rear tires weren't overinflated.

jrct9454

On our C300 Lux, without the sports suspension, we run the std 225/45x17s at 35 psi all around, and have had them as high as 37 psi when we were in Vegas at 100F....the ride has never been anything but superb. For me, this is a big reason I went with the Lux - the standard handling is so good, I think the sports mods are overkill.

[Part of the reason for the higher pressures in our case is that we were carrying a lot of weight on our recent trip - I estimate the total load at over 500 lbs, and it might have been closer to 600 at one point - we were carrying a couple of extra wheel/tire assemblies for a friend, plus all of our luggage, plus all of the junk I normally carry all of the time.]

JimPap

John,

What does the sticker in your door jam say about the inflation pressure?

By the way, my dealer told me today that these tires have nitrogen in them rather than air. Wonder if MB did that of if this was strickly the dealership.

jrct9454

Ours says 29/33, plus more for higher speeds, same as yours.

oblu

Your wheels better have a green cap on the valve then. No real harm should come from mixing since "air" is mostly nitrogen anyway, but still nitro filled tires should technically be labeled with a green cap.

JimPap

Yeah, I was reading about that. Green cap if its nitrogen. Mine aren't green. They're some kind of silver gray.


Now nitro in the tires, that would be something else. First good bump and ka boom.

Seems that opinion is split between nitrogen being of any real benefit.

Is there any kind of nitrogen processor/pump available at the consumer level. I don't really want to go to a tire place just to add a pound or two.

oblu

The point behind nitro is that you never (or so the theory goes) have to add a pound or two. The nitrogen molecules don't migrate through the rubber over time like "air" molecules, and they don't expand and contract in volume with heat like "air" does.

I know for race cars they want an inert gas in the tire to control heat, but in a passenger car it's always sounded a bit like muffler bearings to me.

RLE

<<I can't help but question why the dealer or someone else upstream would have overinflated those front tires by 5 lbs.>>

Nothing more than a careless mechanic with perhaps an iffy tire pressure gauge.

BenzRulez

I like my at 36 psi all round. Like firm feeling. minimum will be 34 psi.

mac911

I was upset about this last week.

Came home from dealer first time and in the morning front tires that are suppose to be 28 or whatever were 33.

Rear tires suppose to be 33 were 43!

I quickly lowered all to what was specified on the door, and the ride is significantly better.

I find it a bit ridiculous it was 10 pounds over in the back. Furthermore, I guess this would be the factory fault, but the oil is significantly over the max line. Any harm there you think?

JimPap

I wouldn't take any chances and reduce oil till it barely touches the top arrow on the dipstick. With these cars, you basically need to suck out the oil with a machine designed to do so. I don't think you can drain it from below. Since its going to be a hassel, you might op to take it to a dealership.


About the tire inflation pressure, who knows what they're doing?? Perhaps 3 lbs over....but 10lbs.