Correct tire pressure
These are cold tire pressures.
1) Gas door flap which indicates
normal load: 30psi front 36psi rear
max load: 33 psi front 42 psi rear
2) Driver B door pillar which indicates 33 psi front 42 psi rear. There is no mention of load.
Is max load the norm? I figure I'd want to keep my tires tuned for 'normal' load.
What should I be keeping the tires at? I just got my car back from its 2nd A service and they pumped all four tires to ~40psi.
I go with the Gas Cap rating, and keep it at "Normal". I actually usually go to 32-33 F, and 35-37 R when I fill it up (then it naturally decreases over time).
I think the B-Pillar rating seems ridiculously high.
Last edited by listerone; Apr 26, 2011 at 09:56 PM.
So I guess the correct answer is -- it doesn't matter! Let's just say somewhere between 30 and 40ish with a bit more in the rear and even side-to-side.
Trending Topics
The Best of Mercedes & AMG
The pressures listed on the B Pillar are the cold settings for the max load/max speed. These are the maximum you should set the pressures on your car and should only be used when the car is fully loaded or if you plan to run at sustained high speeds (think Autobahn, so uncommon in America).
The pressures listed on the gas filler flap give you normal cold pressures and cold max load pressures. For regular driving when not running a full load of people/cargo, the normal cold pressures (lower numbers) should be what you run.
Side note, I'm quite sure the reason for this disparity has to do with lawyers and the old Ford Firestone Explorer debacle. It's easier for Mercedes to tell everyone to over inflate their tires so they're covered for all load conditions (with the negatives being possible increased tires wear, rougher ride, and possible tire/wheel damage from bad roads) compared to someone overloading their car at the lower pressures and having a blow-out due to an overheated tire. It's a shame that Mercedes doesn't list each wheel size setup with the normal and max load settings on the B Pillar or gas flap (or both). It's very nice info to have that info for changing wheel size for winter wheels/tires, etc. At least Mercedes should list every wheel size with normal and max load pressure settings in the owner's manual. BMW does this and it's very handy. They even list different pressures for a M+S tire versus Summer tires, as needed.
Mercedes has chosen to help drivers find the tire pressure they should use under normal driving conditions with the auxilliary label on the gas filler door.
That may be the case but the manufacturers are still free to set things up a few different ways. On a BMW B-Pillar, it lists the normal cold pressures for the wheels that came from the factory on that car and also has a yellow sticker next to that with "over 100 mph" pressures for the wheels that came on the car. The main sticker says to see the owner's manual for more pressure information. The owner's manual then lists the pressure for each and every version as well as wheel size, load type, etc.
Personally, I believe this setup is far better and clearer than the Mercedes setup. Just look at this thread.
List both the partial load and full load/high speed cold tire pressures for the wheels/tires that came from the factory clearly on the B-Pillar and the inside of the fuel filler door. Both places should have a clear note to reference the owner's manual for more information.
The owner's manual should then list every available factory wheel/tire size with the corresponding cold pressures for both partial and full load. The owner's manual should also list the cold pressure for the Mercedes recommended winter tires in the various sizes. The owners manual has all the wheel/tire combination listed already but it doesn't reference any recommended tire pressures other than for the spare. Crazy.
As noted, this setup vote is pretty much exactly how BMW does it (other than BMW doesn't have anything listed on the inside of the fuel filler door, it's only on the B-Pillar).




I use the lower figure and then add two lbs. to that. Periodically I measure tread wear and adjust pressures accordingly if needed. The + 2 lbs. seems to give even wear.
I use a hand pump to add air to my vehicles. That way I can measure when cold and get very precise TP.
BTW, the TPMS indicator in car is fairly reliable, but will often show different pressures per tire. Apparently this is normal and should not be used to determine how much air to add.
My dealer uses the lower figure for my car, probably because I complained about ride. Some may use the higher figure because it supposedly gives better MPG, but doubt it.
Check and set your tires, when cold, to the pressure you deem correct based on the gas filler door. Use your gauge to do it. IMO, humble as my opinion is, ignore the variety of of old-wives' tales, etc, on radical ideas about what tire pressures REALLY should be. Mercedes, and the tire companies know, and there are no big conspiracies out there. (And re: 9/11, either)
THEN, while still cold, reset the TPMS. TPMS will invariably give you numbers different from your gauge. That's expected, and OK . . . you know what they really are.
From that point on, ignore the pressures TPMS presents in COMAND. Just use it as a warning device. If any tire departs markedly from the setting you will get a warning. If you get a warning, use your gauge, while the tires are cold, to confirm that the pressure is different from that you set using the filler door settings. Again, ignore the numbers from TPMS except to get a feeling as to which direction things are going.
IOW, TPMs is not a precision tire pressure device, but it is a hell of a good variance warning device, and safety device, thus it is a great feature.
As for tire wear, the Central Tools 3S401 Digital Tire Tread Depth Gage is a great idea, although kind of expensive. (What are you going to do with all that money? Leave it to your kids?)
Last edited by Live Oak; Feb 21, 2012 at 09:21 PM.




