Dear Sportstick: You're wrong. The 2012 owner's manual (yes, I've read it as I have every car manual I've ever had for 45+ years) has two tire pressure information options: the B pillar AND the inside of the gas filler cover. If I followed the B piller label the rear pressure would be 41 PSA, which is nuts unless you're on the autobahn or carrying three NFL linemen in the back seat as an earlier person said on this thread. This is my fourth Mercedes and the inside gas cover has always listed tire pressure. I've also had three Audis and they've done the same. I'm curious, what pressure do you set the rear tires on your c class? My questioin remains unanswered, probably because the 2012 models haven't been out long enough.

I set my 17" staggered rear tires to 33psi, as the label on the B-pillar advises 28/33 f/r. Interestingly, the values are the same on the fuel door. I looked at my E Class, and the situation is the same...matching values front and rear of 31/35, although the fuel door advises +4 psi for 100mph+.

However, look at this link, which is the closest I could find to the subject at this time. Scroll down about a third of the way to Section IV, Para B. starting with "Vehicle Placard". This describes the label required by NHTSA regs on the B-pillar. The issue may be that the values do include the full load, as you stated, which is more of an issue with lower profile tires having less sidewall to absorb compression. For the 17" tire, the recommended setting provides capability as my loads vary and a good ride/handling balance. If you want to assume only light loads, you could likely run lower, also assuming US highway speeds. This would also provide more ride comfort, as would changing to 17" wheels.

http://www.nhtsa.gov/cars/rules/ruli..._petitions.htm

My 2012 C300 Lux shows just the opposite. The pressures from filler cap are lower (33/38), while the door jam label shows 36/41.

I tried both setting and think 36/41 is too hard for me. Mine now runs 33/36.

The question that seems to be developing is the real intent of the "special circumstances" label (MB's words) on the fuel door. The universally required primary label is on the B-pillar, as noted in the NHTSA document in the above post. Perhaps, a motivated party might contact MBUSA and ask for the definition of "special circumstances".

I think it is important to note that optimal tire pressures depend on a mutitude of variables.

1. Tire manufacturer, size, and compound
2. Load
3. Driving style
4. Driving speeds
5. Weather/climate
6. Road surface
7. ride, fuel economy, handling preferences

No one here can tell you the EXACT recommended pressure for your tires unless they know all of the above. Even in the exact same size of matched staggered 225/40/18 and 255/35/18 tires the recommended pressures could be different whether running an all season 80,000 mile touring tire versus a max performance barely DOT tire.

Even in the same manufacturer and specification, you may live in middle ohio with zero turns and all highway driving and I may live in the mountain of Tennessee and take the "tail of the dragon" home from work every day. The tire pressures will be vastly different.

Like an all season tire, the general recommendations on the B pillar will capture a great majority of drivers and conditions but may not be perfectly optimal to your specific conditions.

Learn to use the little triangles you will find on the sidewalls of your tire. I look at max inflation recommendations of the tire manufacturer and back it down 10 psi or so (in my case 51psi is max recommended pressure). I then experiment with that psi to see if I need to go up or down from there using wear indicators.

I drive agrressively and use wear indicators to see if I am scrubbing over them when cornering aggressively. If I am, I up my pressure a bit. I have ended up running 40 psi F and R in my 225/40/18 and 225/35/18 combo of BS RE760 sports. But that psi gives me even wear, firm ride (you can use tire pressure as added spring rate), and good handling for my driving style. If I drive less aggressively, I may lower it. I also look at my tread patterns for the change in color from dark black to lighter gray to indicate how much of the tread I'm riding on. If you notice it is only the middle 4 or 5 inches in your tread, you are probably over inflated.

cheers! Mike

Considering the fact that your tire pressure gauge has a between 1.2 and 2psi +/- and that the b-pillar is rated at max load and no one stops to let air in/out depending on who becomes a passenger for the day I'd just split the difference. If you're even close to either suggestion (gas cap/b-pillar), you're way ahead of most people anyhow...

2012C350, you are correct. These gauges are not the best unless you get a very expensive one with a cable, etc. The inside filler cap on my 2012 C350 shows 30F, 38(!)R, but in small lettering at the bottom it says "maximum load." My 2008 C350 was consistently set at 30 F and R. M-B service guy I trust suggested a 3 lb. differential, 30F and 33R, and "experiment." 2012C350, when you get the new car check it out and let us know your findings, if you have the time. P.S. Pittsburgh is my hometown. Great city. Best regards.

Oh I'll have time! I'll be talking everyone's ears off about the car when it gets here....

--John

I've asked MBUSA to define "special circumstances", per the owner's manual, in regard to the fuel door pressure values. When I get an answer, I'll post it here. My question went in on the MBAdvisors community website, so I expect to get a response shortly.

Thanks, my first posted reply #2 has been verified.

.

Sportstick,

Hope you don't mind but I wanted to post the response from MBUSA on the MBAdvisors community website :

Here is the clarification directly from our engineers here at MBUSA: The tire pressure indicated on the B-Pillar is the maximum tire pressure under maximum load. Further instructions on vehicle maximum loading can be found within your owner's manual.

The tire pressure range indicated on your fuel filler flap accounts for all other driving situations. The reason optimal tire pressures differ among owners is because driving situations may differ - you may typically have passengers and cargo, whereas another owner may not. "Special circumstances" describes all other load situations except maximum load.

Nick

Nick,
You beat me to it! I was going to share when I got home tonight, but thanks for being proactive. The bottom line is that "special" means "ordinary" to MBUSA, and the b-pillar label is "special" . Seems well thought-out to me!

I've noticed the same thing (I found this thread b/c I was looking for info about tire pressure for the 2012 C-class). My father's 2010 (or 2011) C-class recommends significantly lower pressure. Can't recall if they're using the same tire brands. I've also noticed that the ride in my 2012 is SIGNIFICANTLY bouncier than the our 2011 car (my mom rode in the new car today and said, "You might want to check the tire pressure; it's kind of rough back here..."). Oddly enough, the car seems to be less sensitive to small road irregularities (but more bouncy on things like speed bumps).

I've been tempted to reduce the tire pressure in the rear but worry about safety issues. My understanding is that the suspension was tweaked for 2012, so maybe that's the issue (the little reading I've done suggests that the changes were made to smooth out the ride, although I think the car handles better....)? The steering also feels a touch different....

My 2012 C350 Coupe says 32/32 normal load, 33/42 max load, on the gas flap. It says 33/42 cold on the pillar. My experience with 18" low profile tires with much lighter cars is around 36/39 cold for even tire wear. I can't imagine 33 lbs. on 18" with this weight car. With my 18" wheels, I plan to start around 38/40 cold and see how the shoulder rollover and contact area looks. When I up to 19", the pressure will up also.

FWIW I'm at 36/38 cold. They even out at around 38/40 or 39/41 at highway speeds. I'm happy with them that way - IMO a nice compromise of vehicle dynamics.. economy, comfort and steering feel.

Oh yeah almost forgot these are the AMG 18" sport wheels on factory Continentals.

Cheers,

My C350 with Factory 18's has the same recommendation on both the B pillar and the fuel door: 33F / 38 R. I can't go lower or the TPMRS picks it up.

It doesn't make the back twitchy but I had the same initial thought about the recommendations.

These cars have a good weight distribution so perhaps those recommendations are designed for maximum trunk loading conditions? Whatever it is there is quite a bit of engineering work that went into them. So I'm sure the specs are optimal.

I have 18 inch AMG wheels on my car. I run 32 front. 36 rear per what is in gas flap. Car drives great.

How come? My old 18AMG's required 39 fronts 42 rear.

Are you running yours at normal load or max load?

They have 17" and 18" wheels, depending on model and options

Interesting that this question just came up for me too in my 2014 C250 with 18" wheels. My TPMS kept going off and I thought something was wrong, turns out I wasn't inflating them enough. The dealer was also somewhat confused that the B-pillar sticker and the fuel door sticker being different, but said they always follow what is on the fuel door.

My 2014 C350 says on the B-pillar "EXTRA LOAD" by both, and 39F 42R. On the fuel filler door it says "MAXIMUM LOAD" and 36F 39R. +3 for 100+mph

I am usually the only passenger, so I don't know. I run them at 36F 39R