mistersir

So I checked my tire pressure for the first time since picking up my car last week. The dealer had the pressure set to 40 PSI. WTF? Why was the pressure set so high? I dropped it down to 36 in the front and 38 in the rear. (Door jamb says it should 30 in the front and 35 in the rear)

Anyone know why the dealer would set the pressures that high? If anything, I would assume that they would have followed whatever the manufacturer stated it should be.

sebydeleon

Maybe the dealer did not check pressure at all. If is a new car, is an usual procedure to overinflated tires because the vehicule will be in a ship and un stock for a while

Sportstick

Not sure where you live, but if the car was indoors for a while at the shop and the tires reached ambient temp in the heated garage, he may be allowing for effect of cold weather once you leave. 1 psi per 10 degrees loss. Where and when did you measure the pressure? Is your garage heated? Do you live in a cold weather climate now?

mistersir

I live in cold weather climate (Toronto). Currently about 1 degree celcius right now. My garage is unheated and is probably about 5 degrees celcius. So definitely was taken in the cold. (Also, car has been sitting idle for 7 hours).

I think the previous poster may be right. The dealer didn't check the tire pressure before releasing the vehicle to me. No wonder the ride was so harsh. And here I was blaming the OEM Continental tires. Ok, who are we kidding? The OEM tires still suck. LOL.

Glyn M Ruck

Dealer is either an idiot or did not perform the pre delivery check properly.

JimPap

I've also heard that tires are over inflated at the factory so that the tires won't develop a flat spot while in transet. It only takes a few miles for the tires to warm up and for the flat spot to work its way out. But think about it. You get into a car that's been sitting for a few weeks to do a test drive and due to these flat spots it rides like it has a flat. I think they'd rather you get a firm ride than a bad ride.

As far as tire pressures in general, my 2008 model C300 had always ridden too firm for my taste. This is following instructions and using what is thought of as a high end pressure gage. For whatever reason, I under inflated the tires and the ride improved substantially. I may have just gotten a defective tire pressure gage.

junsny777

I heard that tire pressure needs to follow the kind of tire being used. If your car is equipped with high performance tire. Their PSI usually needs to be higher than a standard all season tire. There should be a maximum PSI# on the sidewall of the tire. I have a Toyo T1R on my other car and the maximum PSI of 50, so the tire shop usually fills it up around 47psi. They said it will help the tire wear evenly and also give you the maximum traction.

Norm01

Ok I'll bite, if the door jam says 30/35 why did you inflate to 36/38.

mistersir

I feel it's too low. When I had my tires at 32 all around, the ride felt quite spongy. I currently have it at 38 all around. The ride seems a bit stiff, so I think I'll drop to 36 all around.

Another thing I found out is that all C-Classes list the tire pressure to be 30/35. So whether you have a C250 with 16"s or a C350 with 18"s, you have to run the same inflation pressure? Doesn't make sense to me at all.

I'm hoping 36 will give me a good balance of comfort, handling and fuel economy.

whiteongrey

Happens to me every time; dealer, tire store - does not matter. First thing I do is check pressure.