I would be very surprised if Mercedes would say something in abracadabra.
This is not German (the words are).

Rob

There are Two Different Inflation Pressures for your tires.

1.The Tire Manufacturer's MAXIMUM Inflation Pressure.
(This is the "DO NOT EXCEED" pressure)
On the Sidewall of the Tire.

2. The Automobile Manufacturer's Recommended Tire Inflation Pressure.
(Some manufacturers [Like Mercedes] give three [or more] versions
of these Inflation Pressures,Based on the Load imposed on the
Vehicle [How Many 100 Lbs bags of sugar if you're a " 'Shiner"]
and/or the Speeds intended.)

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'84 300SD sold
124.128

"Recommended" tire pressure is always a compromise.

Fundamentally, the air pressure in the tire simply must support the load. If there is a 1000 lb. load on the tire and the pressure is 32 psi, the tire will flatten itself so that exactly 31.25 square inches of tread are in contact with the pavement. If the pressure is raised to say, 35 psi, the tire will stand up a bit and only 28.57 square inches will be in contact with the pavement.

Generally, the less tire contact, the less the friction between the tire and the pavement, and the better the fuel economy. However, this is offset by the fact that the round tire will begin to turn into an oval shape and the edges of the tire will begin to lift from the pavement when the pressure climbs to the maximum limits of the tire, simply because the load on the tire is insufficient to keep the width of the tread in contact with the pavement.

Take a look at the sidewall of any tire and you will find the maximum inflation pressure and you will find the maximum load. Most folks never push the tire to the maximum load, and, therefore, they don't ever require the maximum inflation pressure.

If they run maximum inflation pressures with 50% loads, they get fantastic fuel economy, but the shape of the tire under such pressure means that the wear in the middle of the tire will dramatically shorten the life of the tire.

For maximum possible life, there would be a specific inflation pressure for every possible load that the tire will see. If you pile five people in the vehicle, you increase tire pressure to compensate for the load, and vice-versa.

Naturally, nobody does this and the manufacturer of the vehicle must take an "average" load and apply it to the specific tire on the vehicle and make a judgment as to the required inflation pressure. It's hardly the perfect number for any specific driver or vehicle.

Most folks vary the stated pressures slightly to suit their own particular situation. Some folks like a firmer ride with better handling characteristics and they add four pounds to the recommendations. Some don't like the suspension behavior with just the driver aboard and they subtract 3 psi to give a softer ride. They accept the fuel economy penalty.

The "recommendation" is only the best place to begin. The preferred pressure for a specific tire/vehicle combination is always dependent on the combination of load and driver preference.

Good stuff Brian, in line with my practices, but I think you nailed it down a little more for me. With myself and no more than 1 passenger, being that I prefer a firmer ride and better handling, and MPG, without causing undue wear, sounds like the "plus 4" recommendation is the place to be.

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former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL

I find that the recommended tire pressure on the fuel door leads to a feeling like driving on marshmallows. I generally run 35 PSI front to rear. I've never had tire wear issues and the handling is fine.

You'll likely find that the tires have quite a bit of tolerance for pressure that is not perfect for the load. If the tire needs exactly 32 psi to have a perfect shape with a load of 1000 lb., increasing the pressure to 36 psi will change the perfect shape slightly but not significantly enough to affect the tire wear in a way that can be easily noticed by the casual observer. If all the threads are within 1/32", it would take a very accurate measurement for anyone to notice.

You'll find all kinds of people on this thread adjusting pressures to their personal taste. All will state that they don't suffer any undue tire wear. However, if checked very carefully, over a long period of time, I'm quite sure some slight additional wear can be observed in the center of the treads (for overinflation) or at the edges (for underinflation).

Pardon me guys.My tires look flat at max 44 psi.they are 225 60 16 stock size.The outsides are wearing but the insides still have paint.Bought them in Nov,at Wal Mart.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

Right. That's gibberish masquerading as German. No way that's an official MB pronouncement.

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

I figure the engineers have provided numbers for a reason.

I usually take the front/rear recommendations from inside the fuel door and add 2-3 PSI per tire which adds a bit to the fuel mileage. It also assures that if you are a little late in checking the tire pressure next time, you will be that much higher.

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1984 300 SD 384,000 Miles

the only true "gospel" to tire pressure is temperature

here's a picture of a race tire used for setup



you can see the temperature and durometer measurements they were using for alignment and pressure setups

while street tire usage is different it does follow the same parameters. The easiest way to determine what will work best for your use is pretty simple.

get some white shoe polish and mark the sidewall of all four tires

like this


start with a higher than normal pressure and drive around stopping periodically to reduce pressures on all of the tires. When you get to the point that the markings are rubbing off (like in the picture) that will be your base line. Fronts and rears will most likely be at different levels. Now, if you find the car understeering when driven aggressively add a couple of psi to the fronts or reduce by a couple psi in the rear. If you are experiencing oversteer at corner exit reduce pressure in the front or add pressure in the rear.

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