troby

Can please any owners offer some help/advice with the required tire inflation pressure?

I am the new owner of the car, and the owner manual recommends to follow the labels on the car for the required pressure of the tires.

The tires on the car are: Continental 4x4 Contact 255/50R19 - 107H. On the driver's door pillar/sill there are 2 labels recommending 33 psi front and 39 psi for the rear tires.

Recently, during my third gas fill up, I noticed another plate on the inside of the gas cap, with different pressure requirements:

"Normal Load = 32 psi front, 32 psi rear
Full Load = 33 psi front, 39 psi rear "

(When I took delivery of the car all 4 tires had approx. 45 psi, which I lowered).

I want to thank in advance for the time and effort in responding to my silly question.

jon2002

Congrats on your new ml550...I am also a new owner of the same car and have wondered the same thing.

I have the 20" wheels with 265/45-20 Pirellis, and the door sticker says 32f/38r. On the other hand the gas tank reads 32f/32r normal load, and 32f/38r max load.

Personally I have been playing around with the pressures, and find the 32f/38r too firm. Makes the rear end a little skittish over bumpy corners. 32f/32r rides better, but makes the rear tires look very squished. Fronts look equally squished too, but its the "recommended" pressure. I've settled with 32f/35r.

My car also came delivered with too much psi in the tires.

troby

Dear jon2002,

Thank you for your reply & help, and congrats on your new car.
I was a little 'embarrassed' to post this question. But now I can understand that most ML owners will have to go through 'tough' decisions...

Right now I have the front tires at 33-34 psi and considered them 'squished'. Probably I will go also with 32f/35-36r.

Thank you again for the help.

jon2002

Play around with the psi's and let me know what you stick with. Seems to me 32psi is quite low for a 5000lbs vehicle, I imagen ride comfort was a big factor in that number.

For whatever it's worth, the ML63 with 295/40-20s or 295/35-21s recommends 36f/41r.

troby

I was never faced with this particular dilemma before. Every car manufacturer gives a psi number, and the car owner has to stick to that psi. Before posting the question here I did some research on the Internet. It seems that recommendations are in unanimity that is acceptable to have a higher psi, rather than a lower one.
Today I lowered mine to 33 psi front, and 37 psi rear. Wanted to see what shape the tires would take. A day of driving did not enhance the 'squished' look.
Tomorrow I will try to lower all with 1 psi.
I still have a hard time to accept the fact that a reputable company like MB leaves such a decision on the owner's shoulders.

Grau E350

i have a 350 w/ 20" wheels. i'm running suggested normal load 32 front, 32 rear per gas cover.

i did try 34 front, 34 rear and found while the ride was still good, it looked like i was getting some more wear on the outside of the wheels.

i did notice a little wiggle/vibration at the higher pressure, but at the lower pressure is is less or non-existant.

troby

Thank you very much for the help and consideration.

I puzzled by this issue with the tire pressure, and do not fully understand MB position on this. And can not comprehend why ML adds another "secret" label on the gas cap, in addition to the 2 on door sill (where all car manufacturers list the tires psi). But decided to move on.

Right now I have 33 psi front and 35 psi rear. Both tires look strange, like are badly under-inflated. Due to this concern I pay attention at the tires of the other cars on the street. For some reason I feel that my ML tires need some more air, and are begging me to spend 25 cents at an air pump...

Thank you again guys!!

troby

Hi Jonathan,

It feels as we are the founding members of an 'exploration team'.

I always liked to have on cars the same pressure on front & rear tires. 33f/35r seems as the lowest pressure I would go on this car, but with your assurance I would/will go also 35f/35r (or 36r).

Another thought would be the wear on each tire. We do have to do a recommendation for tire rotation as on any other car. But on the ML it seems that the weight distribution would make a different wear on the tires anyway.

Mostly I use public transportation in NYC, and drive in weekends, or evening. So my testing capabilities are somehow limited.

Thank you for the help and advice. (Since I am not alone with this ridiculous problem, now I am assured that I am not crazy.)

Please keep me posted

Robert

troby

Jonathan,

I'm still 'unsettled' on the pressure. Now I am with 33f/36r. Ride is OK, but I don't like the 'Under-inflated' look of the tires. After some time driving the pressure is approx. 37f/41r measured by, and listed on, the TPMS....

Robert

jon2002

Hi Robert,

Try 35f/35r and see what you think. I've been using that lately and i'm still undecided. Steering feels better and is less mushy vs 32f/35r, and the tires look less squashed. I'm not sure on the ride quality though, i wish the car rode smoother over bumpy roads.

If you're into frequent adjusting and playing around with tire pressures, consider picking up a small air compressor from Sears or Homedepot; it's a big convience. Saves you trips to the gas station, and you can tweek your car tires as often as you'd like from the comfort of your garage.

Just curious, but what tire pressure gauge do you use?

troby

Hi Jonathan,

Sorry for the delay in reply.

I never had a problem with the ride quality, just the "look" of the tires. I never got so 'squashed' tires at 'recommended pressure'.

Now I use 33f/36r. Ride is OK. As expected the pressure goes up 4-6 psi while driving in these hot days. I noticed that having the car parked outside in sun, the pressure on the sunny side is 2 psi higher than the side in shade.

The TPMS on the car seems accurate. The gauge I use is a mechanical "Slime" brass with black dial. It has also an air relief valve, which is very helpful to lower the psi to the desired value. I find it accurate and I'm happy with it. I tried couple other models and types, and this one was the one that worked the best for me. Personally I could not find a digital gauge to like, and could not get used with the 0.1 psi increments, despite high recommendations from other fellow drivers.

Thank you for the air compressor tip. I'm a big fan and I have in the trunk 2 portable models. One helped in a weekend to use a flat tire instead of replacing it with the spare. Just inflated the flat tire, took the car to Sears where I bought a new tire (could not find the cause of the leak), and another portable compressor. Ever since I have them with me.

Regarding the tires pressure, my understanding is that we do have different tires. I wonder if there is (are) some difference(s) between 20" and 19". Since it seems that already there are 'multiple personalities' within ML family members...

Cheers,
Robert

azzurribaggio

Does the air go out of these tires pretty frequently? I loaded my 20" tires with 34F-38R, let's see if the sensor still goes off.

troby

In my case the tires keep the pressure. In about 2-3 months, the pressure, in each tire, went down approx. 1 psi. (I think that maybe is possibe to have something to do with the envinronmental change in temperature outside, from summer to fall season ?)

I do not know what the TPMS sensors setting is, in psi, and where do they give a warning.

How is your ride with the 34 psi in front tires? On my 19" tires, the 'jump' fom 32psi to 34 psi makes a 'stiffer' difference in ride quality.

Cheers.

jon2002

I beleive the general rule is: for every drop/increase in 10 degrees of ambient tempurature, the tire psi drops/increases 1psi. I've been adjusting the tire pressures in my cars very frequantly this time of year due to the temperature changes in New england.

azzurribaggio

Haven't tried it out yet, I rarely drive my ML since it's the baby carrier and the babies just turned 3. So we aren't really going out much yet
Since buying the car in April I've had to fill the tank twice now.....but the last time I took the kids for a checkup I was getting "low air" in the tire warnings on the dash.

LOVEMYBS

I also have 20" Pirelii's and run them at 42psi. Cold inflation is 40psi. and max inflation is 50psi. I also use nitrogen vs. air. If you also have TPMS you're going to get sensor alerts at 32psi (I do). The 20" tires should be inflated to 40psi or more or else they are going to wear badly. The owners manual only discusses 19" wheels because they are stock. If you have 19" wheels run them at the recommended psi in the manual. You can also call Tire Rack to discuss this with them, I did.

venchka

Want to know the answer? Ask my wife. She reads the tire pressure for 3 different vehicles from the chart on the GAS FILLER DOOR. Light and full loads. Right there. When you fill up. Assuming you do fill up. Twice since April? My 4 year old granddaughter was already in pre-school, dance class, etc. at 3. Y'all need to get out more.

The door pillar information is for maximum load only. Or trailer towing. Or carpooling with several large football players.

Wayne

roadrutz

Sorry, but I have to disagree with you.

Running your Pirellis at 40 psi is too high. The fronts are significantly over-inflated and will wear quickly. Mercedes recommends 33 front and 39 rear for 20 and 21 inch wheels. While I have every respect for Tire Rack, I would tend to believe Mercedes' engineers first.

Regarding nitrogen ("racing air"): The nitrogen you use is actually 95% nitrogen, as opposed to 78% nitrogen in normal air. If you get it free, it is worth using as it typically contains fractionally less water vapor than does compressed air, but if you have to pay for it the benefits are so small that it really isn't worth it. Most tire places near me charge $5 to $10 a tire to inflate with nitrogen, which is really nothing more than a nice profit centre for them. (You won't find many at Bridgestone dealers, however, as Bridgestone is "officially neutral" about its use. In other words, they think it is a bit of a scam.) I read about a new car dealership that is filling their tires with nitrogen -- or so they say -- and adding $199 to the price of the vehicle! Do you have to go back there every time you top up your tire pressures?

roadrutz

I won't swear to this if you line me up in front of a firing squad, but I believe the pressures on the driver's door are for the actual tires you have installed, while the sticker on the gas filler cap is for generic pressures for 'normal' 17 and 18 inch wheels. On my 550, the door sticker specifically says it is for 21-inch wheels and tires, which is what the vehicle came with, and the pressures are completely different from those on the gas cap.

venchka

That is possible. We are running factory stock wheels & tires on 2 of the 3 vehicles. I will double check vehicle 3 tonight.

However, that still doesn't explain why the door pillar may list the correct tires & wheels, but lists the inflation numbers for maximum load and/or trailer towing. How is an owner supposed to know what the light load inflation pressures are?

Wayne
Content to run 35 psi in his 16" & 20" Scorpions in East Texas.

LOVEMYBS

Thanks for your input. My local indy fills my tires for free so it's not a cost issue. However, if I had to pay for nitrogen I wouldn't as I see no benefit to it. I base this on several AMG track sessions with nitrogen filled tires.

troby

Jonathan,

Thank you for the clarification on the tire pressure drop/increase with ambient temperature. This car is my first MB. In all cars there is one clear recommended pressure, i.e. 33 psi, and the owner keeps the tires aroung that value with the only concern of a consistency in value for all 4 tires.

In ML the process it seems to be more complex. From the recent posts I am getting another challenging scenario: that of tires pressure when an owner wants to change the wheels ...



I am almost sure that on my car, the pressures listed inside the gas cap, and that on the door sill, are for the tires installed on the car. Maybe if the wheels/tires are changed at a dealership as an option, the configuration & pressures will not match.

troby

From the discussions above I just noticed something interesting. According to the owners' statements, the same ML550 model is equipped with different wheels & tires - 19", 20" and 21".
Please correct me if I'm wrong, but I recall that at the time of my purchase, the standard wheels on all M-Class models (except ML63) are 19", with an individual ML550 option for 20" AMG 5-spoke wheels. I do not recall seeing a 21" option.
Also when I got my car, the wheel/tire size choice was limited to just what was fitted on each car at the time of purchase, with an option, for the entire car, to take it or leave it.
Does anyone know what the reasoning behind the diversity of tires sizes offering is? Also how MB advertised all tire options and if potential customers had a possibility of choosing the tires size at the time of purchase? I'm just curious.

jon2002

If i'm am not mistaken, the canadian market ML550's offered a 5 spoke 21" wheel option...I beleive it is a 21x9", with a 265/40-21 tire. I am curious what particular tire was used for that wheel size.

In the interest of ride comfort, I've been sticking to the gas cap psi recommendation of 32f/32r for my normal load and every day driving with my oem 20"s. The tires seem to absorb bumps better. Seems that the car does steer better at high speeds on long highway trips at 35f/35r, and gets a little better mpg, at the sacrifice of a slightly bumpier ride.

Jonathan

Moto One

Something for all to consider. The recommended tire pressure has to do with not only tire wear, but also how the suspension is tuned (i.e. high speed shock damping primarily ) The tire pressure is a very important part in ride control. Too high of pressure and you will feel what is called "Tramlining" its a double/triple bounce of the suspension upon hitting small sharp inputs (bumps/ridges). In effect it's causing the tire to loose contact with the road surface thus limiting traction on ruff surfaces, and will cause early activation of the ABS system under hard or sometimes normal braking. This is even more important with low profile tire on larger (more mass sometime) wheels.
If you really dig deep, you will find out that there are certain tires that are recommended not to be used, because of side wall construction that causes the same effect to the suspension operation when inflated to recommended pressures.

Mark