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Just took delivery in the USA of a 2020 GLC 300 AWD, 2.0 turbo, 18" wheels.
Trying to understand the correct tire pressure, but there are three separate tire pressure placards: two on the B pillar, one on the fuel filler door, and they are all different. Which of these three do people normally follow?
dealer said: use the placard from the fuel filler door
My dealer said to use the fuel filler door placard
after looking a little closer:
B pillar placard #1 = maximum load from the fuel filler door + 4 psi for driving over 100 mph
B pillar placard #2 = maximum load from the fuel filler door
From my perspective, this is confusing. But now I have what I need.
Yes, fuel door reading is the correct pressure — 32 psi all around, year round. You must adjust pressure for seasonal temperature fluctuations. My Michelin dealer doubted the 32 psi recommendation thinking it is too low, but after evaluating my tire wear at tire rotation intervals, he admits that 32 psi provides a comfortable ride with an even wear pattern.
On Feb.16 upon taking delivery of a GLC myself and many other GLC drivers were confused with regard to tire pressure. And I see today the situation has not changed. The number of posts here concerning tire pressure is too numerous to count. Why is it taking so long for M-B to correct a simple issue as elimination of confusing data on a decal
The tire pressure data on the inside of the fuel filler door is what drivers should follow.
There is no one definitive answer to which is the correct or best pressure.
There is a broad range which is safe and individual requirements and environments may dictate which is 'best'!
You can partly thank the US DOT and your fellow citizens for part of this confusion. All three placards are valid, you just have to understand what they are saying. The white placard is mandated by the US DOT to show the absolute maximum recommended tire pressure, which is the max load recommended tire pressure from the fuel door sticker +4 psi for driving over 100 mph. Ever since the Firestone debacle in the 90s, the DOT requires that the white sticker indicates the safest recommended pressure, which is always the highest recommended and in this case assumes that one might indeed drive over 100 mph occasionally with a fully loaded car whether legal or not. While this is the safest pressure, it'll lead to a poor ride quality. Max load recommended tire pressure means maximum number of passengers in the car plus fully loaded with cargo. For normal daily driving with little or no cargo and 2-3 passengers you should use the normal load recommended tire pressure as indicated on the fuel door. Looks like the fuel door sticker of the GLC is a bit light in information. For comparison, below is the one from my C63S Coupe. You can see better under which conditions the recommended tire pressures apply, but it's always the same. It's a function of load and speed. The heavier the car, the higher the tire pressure should be and same for the faster you intend to drive as the forces put on the tires at those very high speeds increase. The reality is that you should always adjust the tire pressure regularly based on ambient temperature and load of the car. Unfortunately, very few people in North America understand this concept and it is what has lead to all those accidents with SUVs and Firestone tires where they flipped over and people got killed as a consequence. Since Americans in particular apparently can't be trusted with understanding when they need to adjust the tire pressure and which one to use, the DOT has decided to put a white sticker on the B-pillar with a single recommended tire pressure that's safe under any condition and those who don't understand this will just have to live with an unnecessarily harsh ride. Ultimately, there's zero actual confusing information here. The problem is rather that driver education in this country is a joke, and nobody is being taught this.
Last edited by superswiss; 04-12-2020 at 05:16 AM.
You can partly thank the US DOT and your fellow citizens for part of this confusion. All three placards are valid, you just have to understand what they are saying. The white placard is mandated by the US DOT to show the absolute maximum recommended tire pressure, which is the max load recommended tire pressure from the fuel door sticker +4 psi for driving over 100 mph. Ever since the Firestone debacle in the 90s, the DOT requires that the white sticker indicates the safest recommended pressure, which is always the highest recommended and in this case assumes that one might indeed drive over 100 mph occasionally with a fully loaded car whether legal or not. While this is the safest pressure, it'll lead to a poor ride quality. Max load recommended tire pressure means maximum number of passengers in the car plus fully loaded with cargo. For normal daily driving with little or no cargo and 2-3 passengers you should use the normal load recommended tire pressure as indicated on the fuel door. Looks like the fuel door sticker of the GLC is a bit light in information. For comparison, below is the one from my C63S Coupe. You can see better under which conditions the recommended tire pressures apply, but it's always the same. It's a function of load and speed. The heavier the car, the higher the tire pressure should be and same for the faster you intend to drive as the forces put on the tires at those very high speeds increase. The reality is that you should always adjust the tire pressure regularly based on ambient temperature and load of the car. Unfortunately, very few people in North America understand this concept and it is what has lead to all those accidents with SUVs and Firestone tires where they flipped over and people got killed as a consequence. Since Americans in particular apparently can't be trusted with understanding when they need to adjust the tire pressure and which one to use, the DOT has decided to put a white sticker on the B-pillar with a single recommended tire pressure that's safe under any condition and those who don't understand this will just have to live with an unnecessarily harsh ride. Ultimately, there's zero actual confusing information here. The problem is rather that driver education in this country is a joke, and nobody is being taught this.
Brilliant reply, both informative and concise. Thank you
Just want to throw out there that the three values don't even reconcile on my car, a 2019 GLE400, so I don't think the reasoning we decided here is necessarily correct but could just be a coincidence. In fact, in my case, both stickers in the front match, but those values are not the same as the maximum psi displayed at the fuel filler. Furthermore, it seems like even the selling MB dealer believed the front ones to be correct!
In my case (on a GLE):
B pillar placard #1 Front (white): 45 psi, Rear: 48 psi, Spare: 60 psi (cold psi)
B pillar placard #2 Front (black): 45 psi, rear: 48 psi (cold psi)
Fuel filler door:
normal load: front 32 psi, rear 33 psi (cold psi)
maximum load: front 40 psi, rear 44 psi (cold psi)
warm tires: Up to +4 psi
driving over 100mph: +4 psi
The only values that make reasonable sense for a car under normal use, of course, are the ones listed on the fuel filler door. The Mercedes Me app, which reports tire pressures remotely, also says to use the pressures listed on the fuel filler door.
P.S. I think the reason my TPMS warning came on even though tire pressures hadn't changed and had been at the door psi's since I got the car from the dealer, is instead the spare tire must also be monitored even though it isn't displayed on the screen and it had gotten low.
Well after spending over an hour on Google, there is only one consensus answer. That is using the Fuel Door label. Mine says 32-32 normal load for my 2020 GLE 350 4 matic. The dealer delivered the car with the max load PSI settings. I lowered them to 33-33 and have been happy with ride. I did just change the original Bridgestone runflats to Michelin Lattitude Tour HP. Both 250/55 R19 H tire size. Costco set the PSI to max load settings. I lowered them to 33-33. The Michelin's are not run flats and are quieter and ride softer than the Bridgestones. The confusion regarding this is incredible. Every website I go to has a different answer. Tirepressure.com seems to have a very exhaustive listing for various sizes and trims. Their numbers are 34-39 on the low end. Running the proper tire pressure is a pretty important thing and it seems that nobody really agrees on the correct numbers. For now I am going by the fuel filler door label until someone can be more definitive.
Hello, I have a question about these tire pressures. My 2022 GLC300 has the same 3 different pressure recommendations. However I have a warning now stating pressure problems and all the tires read 36psi which is higher than the 32 on all 4 on the fuel door. Should I be lowering the PSI to 32 on all 4? I just want to make sure I run the right pressures. I have the pirelli scorpion verde 255/45/R20 tires on it.
You should set the pressure to your desired pressure, whatever that may be. You then need to reset the TMPS so that it knows what the 'normal' pressure is and your warning should go away.
The issue with that is my desired pressure might not be the best pressure for the tire. I called a dealer and said 40psi on all tires, which seems too high in my limited knowledge, another service tech said 32psi on all 4 but when I told him that my tires were reading 36 he said that it was fine and that I could reset the setting to 36, which again seems like an answer to get out of the issue. I'll wait till the morning and reset the tires to 32 psi cold. that seems to be the correct psi for the tire and car combo.. I'm hoping.
I had the very same issue this summer with my 2021 GLC300 AWD. After getting a low tire pressure warning, I used the higher end values and set all my tires to the recommended 40 PSI. I did notice subsequently that my ride immediately improved significantly: fewer jarring bumps on pothole-riddled roads and a smoother drive overall.
however, when I brought the car in for its first year service, the dealer lowered the pressure in all tires, stating that the pressure on the fuel tank door is the correct pressure. My smooth ride went away, but I guess that’s the preferred pressure for these factory run flats tires.
QUOTE=XMZ XCZ;8019820]Just took delivery in the USA of a 2020 GLC 300 AWD, 2.0 turbo, 18" wheels.
Trying to understand the correct tire pressure, but there are three separate tire pressure placards: two on the B pillar, one on the fuel filler door, and they are all different. Which of these three do people normally follow?
Ahh, a tire pressure thread. Goody! (Not quite as exciting as an 'Oil Thread of Death'. I've seen those go 100 pages easy. LOL)
The pressure on the sidewall is generally the "Max Load" of the tire, not max pressure. I.E., the pressure at which the tire manufacturer has determined the tire will safely handle the most vehicle weight. That pressure is rarely ever within 10 or 12 psi of the correct pressure for your particular car.
The weight on each axle, v.s the tire sidewall stiffness is mostly what determines correct tire pressure.
Drive a car hard and then measure the temps across the tire with a tire pyrometer, and if the center blocks of thread are warmer than the blocks an inch from the edge, then it's is over-inflated. Center colder than the sides and it's under inflated.
With motorcycles, you inflate the cold tires to the manufacturer specs, then ride the bike hard down a twisty road, then stop and measure the tire pressures again. They should have grown in pressure by 10% (I.E. from 33 to 36.3 psi). If they grew less than 10%, you were OVER inflated to begin with. Start off tomorrow with 31. And visa-versa.
This is because an underinflated tire gets worked harder (flexes more as it rolls), and so will gain more heat, and therefore pressure. Overinflated does not flex nearly as much, so less heat/pressure gain.
With cars it's better just to use a probing style tire pyrometer across the tread, and see if the center of the tire is the average of the sides. Or,... you can note the wear on your tires over a few years and see if they are wearing more at the sides than the center. More wear at the center means you are generally running over-inflated, and visa versa.
I tend to run a couple pounds under-inflated in modern cars, as the fashion of huge rims makes for a poor ride, and I'm willing to trade a few thousand miles of tire life for a slightly better ride.
Usually the pressures in a cars door jamb are real close to correct (and I run 1-2 psi under that). For some reason these Mercs though also have stickers in the fuel door, which seem more on the mark.
My E550 will run different pressures than most of the cars here, and of course non-stock tire sizes changes the required pressures by a couple pounds usually.
03-31-2020, 08:49 AM
