The warning or alert to correct tire pressure is based on it falling a bit below the point at which it was initially set. If I recall, when you display the tire pressure, regardless of what pressure you presently have in your tires, you can set that as your start point. For example, if you set all four tires at 37psi, you'll get an alert when it falls a bit below that. My guess is that you would get an alert when the cold pressure is 34psi or so. Anyway, that's what I recall.

My guess is that when they set your start point, your tires were probably around 35psi.

 

Again, the "pillar" info is nonsensical for all models Mercedes - on GL550's they come in from the factory shipped at 45 PSI - and out tech guys evacuate and do Nitrofill at 35 PSI a bit over fuel filler door recommendation.

The TPMS system is sensitive due to it's function to quickly detect any on-the-road punctures quickly - and usually will setoff when there is more than 1lb differential with any one/or-more tires - which can happen easily in such situations on sun hitting one side of the car over another - quick weather change - etc.

TPMS can be rest - after system is initialized - from the insturment cluster.

Yes - tire pressure is a personal choice - have fun with it - but the TPMS system should not be used to set tire pressure - use a quality gauge !

Keep the beat !

 

I brought up same question a few months ago in the 63 section. RENNtech recommended 40psi all the way around but, I found at that pressure and more, I had a bad chassis shutter. I'm currently running at 38 all around and seems good but the shutter rears it's ugly head over particularly rough railroad tracks or the like. I went as low as 33 all around but, didn't feel right to me..to mushy. I've also been as high as 47 and was just too rough and too much shutter.

 

Sounds about right, I ran 45psi in the rears with 20" wheels and was shuttering when braking. I'm running 36/38 psi now to see if there's a difference.

 

 

Tire pressure is a compromise. Anything above the lowest safe pressure for the weight carried and below the maximum on the tire sidewall.

 

32 PSI at all corners is the factory recommend pressure for normal loads in order to give the best ride and even tire wear all around.

 

I bet that on the compromise of 32 psi, tire wear took a back seat to ride comfort.
In general, tire wear is reduced with higher pressure, right up to the safe limit of the tires.

 

40 PSI at all corners to reduce tire squeal and wear. Even then the original set of Continentals wore out at 13,000 and the second set needs replacing at 12,000.

 

How did they wear out?
Center? Edges? Inner? Outer?

 

Both sets wore out at the inside and outside edges. The edges were not only worn, but also 'scalloped' so the tires got increasingly noisy. I had expected that maintaining higher tire pressure would prevent this, but no so,

Fortunately, the ride quality remained constant, which I attribute to the GL550 air suspension.

 

I am guessing the front wore the outside edges and the rear wore the inside.
Do you carry a lot of weight and/or tow?

 

I know the front tires wore the outside edge ... didn't check the rear tires, but I will. We neither tow nor carry a lot of weight ... usually two persons and occasional packages, but nothing heavy. It would be easier to accept this if we did!

 

You are wrong on all accounts.

 

Enlighten me.

Point by point, since I am wrong on all accounts.

 

I use my GL fairly hard, but don't drive it agressevly.
I know that heavy loads and towing will definitely wear the inner edges of the rear tires.
And, of course we all forget to rotate the tires as often as we should.

 

32 psi is not a "compromise". It is the manufacturer recommended pressure at all 4 corners for normal loads and maintained speed under 100 mph. It will ensure the longest tire life and even wear of tires that meet the load specs of MB for these rigs. Tire wear is not reduced when running higher than recommended pressure. In fact, the tires will wear out faster if over or under inflated. Over inflation causes the centers of the tires to wear prematurely. Under inflation will cause the inner and outer edges to wear out prematurely.

There are plenty of articles that you can reference online to explain this to you.

 

Do point out Front has only Toe directional adjustment.

No Camber or Caster to adjust tire contact angles to resolve costly, premature edge tire wear.

On rear there is Camber and Toe. K-MAC kit doubles the adjustment range.

Kits replace the 4 front highest wearing (expensive OEM) bushings at the same time -- Re instating from the early 90's full adjustment allowing for other than showroom height conditions encountered in day to day commuting - high cambered roads, fitting wide profile tires, altered height through load carrying or lowering. With ongoing adjustment for curb knock damage.


W166, X166, W251, C292
Front Camber & Caster P/N 504016 M $595
Rear Camber & Toe P/N 504026 K $480

Delivery Worldwide one kit $30 (F/R) $50

PayPay, Visa, M/Card

 

Sure, there is one magic number.

Everything in engineering is a compromise.
Optimum at empty is suboptimum when loaded normally
Optimum when loaded normally is suboptimum when empty or loaded heavy
The Optimum point also shifts with temperature, speed, and other factors.
That is why it is a compromise.

The biggest factor in tire pressure is safety.
Too low for the load and the tire generates excessive heat due to the flexing that occurs when the tire flattens out against the road surface and then returns to round when not in contact.
Too high and the tire is unable to flex sufficiently to withstand normal surface imperfections and minor impacts without damage.

After that (Now in the safe zone) we have two counter variables.
In general ride improves with lower pressure, and wear improves with higher pressure.
Not only edges wear at lower pressure but the greater the tire flex and squirm the more the tire wears. Both increase at lower pressures.
As for the increase in the center, that was quite common on bias ply tire and most prominent on wide tires.
Today with radial tires it would be very hard to wear out the center due to being at the high end of the safe range (distinctly different from being "over inflated")
You might see the center get to the tread bars first, but even in those cases (Mostly highway driving with a very well aligned car, and well rotated tires) you would still get more life than at lower pressures.

The next factor is handling, and this is a bit subjective. In general it improves with greater pressure up to the point you exceed the suspension's capability to maintain good road contact.
Some cars that is almost to the top safe pressure, and on other cars (usually when you are carrying a lot of unsprung weight, like our GLs) it is lower.
Too low and hard cornering will roll the tire over on the sidewall to far, too high and the edge tread is not compliant enough to be useful.
And off the races!

 

Thank you for that Bill Nye the Science Guy. I'll be sticking to the mfr recommended tire pressure so I can get even tire wear and the longest life out of my tires. I trust the MB engineers over conflicting info from non-Benz non-engineers on an internet forum. These heavy rigs chew up tires quickly no matter what you do....so squeezing an extra 3-5k miles out of a set and having them safer with even tread wear means I'll be keeping them at 32-34 psi all around. You are free to do whatever you can convince yourself is the right thing to do. It's your money and safety.

 

Maybe you should have just said you like the MFGs recommendation and like to follow it, instead of believing that it is "perfect" and what I posted was incorrect.

Did you know that hydroplaning speed is directly related to tire pressure and high pressure reduces the occurrence of hydroplaning, or that the tendency to sink into a soft surface (like sand and mud) is directly related to tire pressure and a lower pressure will reduce sinking and the chance of getting stuck.

Many compromises.

Here is a good one that directly relates to our MB recommendations.

If 32 is good enough for tooling around town, but 36 is needed for 100 MPH, what causes the sudden shift?
And while 32 is good for normal load, but you need 35 and 41 for maximum load, (again tooling around town)
And all those go up 4 PSI at 100, should they go up 2 PSI at 75?
Really, just what should be the minimum for pulling a trailer for extended periods (hours on end) over 75 MPH on a hot day?

 

Perhaps you should pose your questions to an MB engineer. They test these vehicles for hundreds of thousands of miles before they are ever allowed to be sold to the public. And they are the ones who set the recommendations. So I trust that they got it right since they are liable for safety issues and performance.

Did you know that you get the best traction at all speeds and driving conditions by following the mfr recommendations for tire pressure? That includes hot, cold, dry, wet, & snow. These are not serious off-roading vehicles. If they were, I'm sure MB would have different recommendations for those conditions. And they would likely entail some serious off-road tires and a lift kit....which would likely kill the Airmatic suspension.

Pulling a heavy trailer has a different rear tire air pressure recommendation. I think it's around 42-44 PSI IIRC. Look at the sticker on your gas cap door and it will tell you.

Like I mentioned, I really don't care how much air you run in your tires. It's your safety and money. I just don't want others who search the forum looking for answers (and may come across this thread) turning to bad advice and putting themselves at risk.

 

Don't take this the wrong way, but this is getting very interesting.

Yes, they set the recommendation based on a lot of compromises including their target customers expectation of ride comfort.

I trust they got it "about right" for the set of compromises they chose.

Then you think a little bit and you realize that they are setting what basically becomes the safe minimum, with almost every other road condition requiring an increase in pressure. (From their (god given) sticker; More load, more pressure, more speed more pressure)

Do you know what that word means.
I am confident that you believe that you get the best traction at all speeds and driving conditions by following the mfr recommendations for tire pressure. But I don't think you KNOW it.
I am actually pretty sure you don't.

You sure?

More serious than some and less serious than others. (My GL320 is 4WD #10, and I keep cars a long time)

You sure?
https://www.mbsugarland.com/the-on-off-road-package/
The non-US off-road package used to even include an extra 3" of airmatic lift (just like my air-suspension VW Touareg)

The sticker give me a good starting point. But again, I almost always go well above the compromised recommendation (but below the safe limit of the tires)

I would hope they have the ability to read and comprehend, but would love to understand of the lack of safety of my recommendation that you believe exists.

 

I just had my 450 serviced last week (service B) and they put all 4 tires at 41 psi. I agree it is confusing as none of the tire pressure recommendation placards seem to match. Anyway, I thought the truck drove and handled better when I had them set to 37.

 

It's obvious that you think you've got all of the answers and think MB engineers made all kinds of compromises when coming up with recommended tire pressures for different driving conditions. Instead of making all kinds of assumptions based on your vast knowledge from reading others opinions of different vehicles on different forums, it would be best to leave it up to the guys who actually built and tested the crap out of these trucks. Hint: those guys are A LOT smarter than you are when it comes to these trucks.

Your service adviser can likely point you in the right direction to get the real answers from MB.