amolak

What PSI would you recommend for these tyres on my
S280 1998 UK W140?
As the wheels (18"x8.5") and tyres are larger than normal, I would think that the chart on the petrol cap does not apply.

thanks

Amo

PKMBZS500

I do have the exact same question regarding front and rear tire psi for 255/45/18 ( Dunlop sp 9000) on a '95 S500.

Thanks.

-patrick

Mark Pedersen

I run 36 psi in the same size tires on my 1995 S600 coupe.

PKMBZS500

Mmmmmm......interesting.
I was told by someone on the other MB board that since it's the air pressure that's supporting the car so it really doesn't matter what size tires you run. That is, regardless the size of your tires, as long as you keep the same PSI recommended by the factory (ie. figures on the sticker inside the fuel flap or owner's manual).

So who's correct???

Mark-- Running 36psi at all 4 corners? Does that give you any uneven wear...such as wearing the middle or the outter edge?

Still looking for the correct psi.......HELP

Mark Pedersen

Running 36 on all 4 corners. The tires are about gone now after 35,000 miles, Wear was a little higher in the middle and will try 35 all the way around this time.

ychachad

36 psi is high for all 4 wheels for MB. I think the correct pressure is somewhere around 30 F/30R, and 30F/36R for max load. When going to a wider tyre, the weight of the car remaining the same, one actually has to drop the tyre pressure slightly to compensate for the wider tyre. Really, drop the recommended pressures by about 1 or 2 psi. But I think 30 is good all round.
Y. Chachad

PKMBZS500

Boy..oh..boy. I'm really confused now. It seems like this psi figure is all over the place. Some suggested factory settings of 28F/29R ( for a W140 S500) while others recommended 36 all around. Perhaps any number between 28 and 36 would be a good guess then...?

Can any tech guru on this board please answer this simple question?...or does anybody know any tire expert that we can ask?

TIA.

///S320

Click on the link below:

http://benzworld.org/forums/messages...8&id=27&view=t

Mark Pedersen

I wouldn't want to hit a pothole with 30 psi in a 45 profile tire. I don't know anyone running that low a pressure.

ychachad

The higher the tyre pressure, the bigger the hit. 30 psi would dampen the blow more than 40 psi. Your theory is skewed.

PKMBZS500

I ran 29F and 30R for a couple of days last week and they were definitely WAY too low. Currently I'm running 33F and 34R...as a compromise. Unless someone can come up with figures directly from the factory. I remember back in '97 ( correct me if I'm wrong ) there was a so called "Grand Edition" of W140 S500 in the states and I believe they were shod with 255/45/18 stock tires.

Mark Pedersen

Dr. Chachad:

I beg to differ on the question of tire pressure and pot holes. Less pressure allows more compression and more likelyhood of rim damage. I checked with two tire people who concur. I have 35, 40 and 45 profile tires on 3 different cars and run minimum 35 lbs pressure. One car was wearing outside edges at 34, but wears evenly at 38 lbs.

Mark

MPM77

All this tire pressure stuff is a bit confusing. Isn't the factory recommended tire pressure based off the weight of the vehicle not the rim size? For example, a friend of mine had a 77 Eldorado (about 225 inches and 5,200lbs) with the same brand (MXV4) and size tires as a 00 Linc Continental (about 206 inches and much less than 5,200lbs). However, the factory recommended tire pressure was 24psi for the front in the Eldo compared to 29psi in the front for the Linc.

I can't say that I agree with the previous post. How can you say less pressure causes more compression and more likely rim damage? Compression is exactly what you want! An over-inflated tire will not have much compression over bumps and would be more prone to a blowout. On the other hand, too much compression (under inflated) would lead to rim damage.

Mark Pedersen

It's easy - less pressure allows more physical compression of the tire when the tire hits the edge of the pothole. Higher pressure does not allow as much distortion of the tire, protecting the rim better. I put new rears on the S600 tonight and am running 40 Lbs at the suggestion of the mechanic who installed them. Will adjust for best compromise of wear and comfort. I can say unequivocally that 30 Lbs will not work well in low profile tires for me.

ychachad

You are absolutely correct. Too low a tyre pressure, like 15 psi will lead to rim damage. Not a 30 psi. 30 psi will provide some cushion for the tyre to deform, and absorb shocks. Tyres absorb the shocks before the suspension does. Have you ever seen a long, long bridge that is absolutely stiff? the wind would break it. It has to flex a bit to provide the best performance. In the end, run 50 psi if you wish, who cares?

Mark Pedersen

Dr Chachad:

Run 30 lbs in low profile tires and tell me in the end what your wear pattern and rim condition are, I will be interested. One of my friends hit a pothole in his new sl500 with 32 lbs and will now be getting a new rim. No disrespect, I just think you are wrong.