mjeagent

What psi are you guys running in your tires? I got my car back from the dealership and they had the psi at around 40. I brought it to my local tire shop because one of the tires had a nail in it. Asked them to but nitrogen in all the tires and when i got the car back all four were a little over 50psi. I feel shimmying in the back tires - not sure if that's because they are too inflated. Thoughts?

Terminator2029

The recommended tire pressure can be found on a label on the driver's door. The 20" tires are recommended to have 36 PSI (front) and 39 PSI (rear). Everything above cannot be easily justified.

mjeagent

I know but my label says 50psi front and 51psi rear in cold temp. Seems VERY high.

Terminator2029

Sorry, I just realized that your car is not a typical W222. The recommended PSI for the S65 (accordingly to the factory label) is 49 (front) and 51 (rear). That means that there is nothing wrong with having just a bit over 50 PSI on all tires.

hyperion667

I'm usually in the upper 40's, that's after they've warmed up, I have a 265/35/20 all around, I also think N is a big scam

Mitch Alsup

There are a couple of situations where Nitrogen is the better inflation gas.
1) Big trucks where tire temperatures are elevated for long periods of time and many many miles (100K miles+). The lack of oxygen in the gas retards the breakdown of the rubber of the carcass and allows it to be retreaded more times.

2) Race track use where tire temperatures near the boiling point of water (200dF). Here water vapor in the gas boils and dramatically increases tire pressures, making it harder to control the tire pressures, whereas Nitrogen is dry and does not suffer from this.

3) Seldom used cars where the car sits around forever, driven seldom. Here lack of oxygen slows the breakdown of the interior of the tire. Think 1924 Type 34 Bugatti Race (n.e. show) car that is driven twice a year for 5 miles each and the tires will never actually wear out.

Other than these cases, selling nitrogen as an inflation gas is a scam, however, giving nitrogen away for free actually has some benefits.

hyperion667

true Mitch, true

Mitch Alsup

Bringing this back up to actually answer the original question::
The placards on my S600 contain::

A) the drivers door B-pillar indicates 36 Front and 38 Rear is the correct cold tire pressures.

B) the placard in the fuel (gasoline) door indicates 33 Front and 35 Rear cold and 36/38 hot (==warm.)

So, my guess is that anything in the 33-38 range is acceptable tire pressures as long as high performance driving is not in the cards. If high performance driving is (IS) in the cards, the a probe tipped pyrometer to measure tire temperatures is a better indicator of tire performance than pressure any day.

But, I wonder if the sorry* performance of the run flats is a symptom of these higher tire pressures? (*) lousy comfort under normal S-class driving conditions.