I recently put 4 new tires on my 380 sl and I was wondering if the cold inflation should be what is stated on the new tires or should I keep them at the posted psi on my gas door? The posted says 32 in back and 36 in front. The new tires say 40 psi. I compromised and put them all at 36.
I put the exact same size tires on btw..
Panzer

The gas door is accurate for the same size tires, sidewall pressure is for max. rated load at max. rated speed.

More pressure usually doesn't hurt anything within the limits of the tire (sidewall max)other than ride quality, can help fuel mileage slightly. Handlling could suffer if the difference between axles isn't maintained, the pressures on the fuel flap probably keep the car at a mild understeer.

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- Jeff

Panzer, surprised to hear that the fuel filler door calls for a higher inflation pressure for the front tires. Any MB automobile that I have encountered calls for a higher rear tire pressure than the front tires. As long as you don't exceed the maximim inflation pressure indicated on the tire you should be fine. Realize that using the maximum pressure may cause the middle of the tread to wear faster than the edges. I typically run our tires about 4psi higher than the fuel filler door figures.

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Fred Hoelzle

I had my numbers inverted from front to back!! (On the post not on the car) The car has some extra play in the steering so I will leave it at 36, the last thing is need is oversteering! ZOOOOOM!

Max load capacity is achieved at 36psi for a standard load tire and at 42psi for an extra load tire not at the maximum air pressure branded on the sidewall. Adding more pressure beyond 36/42 will change the ride quality but, not the load capacity.

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My tires say 130psi, I guess Michelin doesn't know, I'll forward your information to Michelin's Engineers LOL.

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- Jeff

I've found that with every car I own, the vehicle MFG's recommended tire pressure is the way to go for best ride quality and performance. In fact, its become an annoyance of mine to have to adjust (lower) tire pressure everytime one of the cars goes in for service.

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1982 240 D, 308,000 - 321,127 miles (sold)
1982 300 TD,166,500 - 226,000 miles
1998 E 320, 120,000 - 144,000 miles
2005 C 230 K, 26,000 - 77,000 miles (sold)

x2.
Annoying to have to adjust the air pressure because so many service techs think that the sidewall pressure is what should be in the tires, ...

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Gone to the dark side

- Jeff

and they will agree with me ...

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Thank you everyone for the informative posts! I shall adjust my tire pressure to the recommended amount on my fuel door! THANKS! now for that pesky O2 sensor, and hot start problem...at least it will drive and handle well, WHEN I get it re-started and IF I don't run outta gas....still love this car!

Umm, I've worked with Michelin Engineers, they don't. You might try calling and talking to an Engineer, there is a reason that they mold the max. tire pressure on the sidewall and max. load & speed capacity, and it's not so that tire salesmen can challenge it.

There is a load and pressure chart available from Michelin for each tire.

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- Jeff

the facts are the facts

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and here you will see that load/inflation tables for p-metric and Euro Metric standard load tires do not exceed 36 psi because that is where a tire reaches it's maximum capacity

example:
Michelin item number 54947 is a 225/60-16 Michelin Energy MXV4 plus with a 102H service description and a maximum inflation pressure of 50 psi and a maximum load capacity of 1874 lbs.

As the load/ inflation table clearly shows the 102 index reaches maximum capacity at 36 psi so, putting 50 psi is not going to raise the tires maximum load capacity

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I don't see anything there from the manufacturer, only from Tire Rack, and I don't see anything that supports your statement that the tire pressure on the sidewall is not correct.

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- Jeff

right click the table to see the properties and you will find

http://www.falkentire.com/images/standard_table.gif

which obviously is directly from a tire manufacturer. All tire compnaies i.e. Michelin, Bridgestone, Yokohama, Goodyear, Pirelli, etc. all use the EXACT same tables

reread what I posted and you will see I never said that the max tire pressure branded on the sidewall is incorrect

here is a graph illustrating tire load capacity vs. air pressure (also from a tire manufacturer)

as it clearly shows a tire reaches maximum load capacity well before maximum inflation pressure

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