gussy81

Hi,

This may seem like a silly question but I've always just put the max psi allowed for tyre into my previous cars. So if tyre said psi max was 40 I would put that in..

So I now have the e class w212 model. 2013.

Tyres I have are : 245/45ZR1799W

The tyre states max psi: 50.

I have checked tyre code on sticker on fuel door and matched with my load of generally 1-2 people and got a result of 32psi for my particular tyre.
​​​​​​
Does this sound right or am I massively under inflating my tyre.

Thanks in advanceG

pierrejoliat

I believe the fuel door calls for 36 psi, with tires inflated to 32 psi you get a nice soft ride but you run more of a risk of bending or cracking a rim on chuckholes. I think the pressure should be increased in the back if you have a trunk full of luggage and people in the back seat to 42 psi, but I don't have a full carload usually and if it's just my wife and I, with a trunkload of luggage, I use 38 psi in the back for road trips.

DFWdude

Here we go again...

Opinions on tire pressure vary here as much as opinions on how many fairies live on the head of a straight pin.

Whether to read what's in the fuel door as gospel.. or what's printed in the manual... or what's molded onto the tire itself.

Because tire manufacturers have an (educated) opinion on how their tires are designed, manufactured, and should be used, I start by reading what is molded on the tire itself.

As you noted, the tire reads "50 PSI Max" This is the upper limit (measured while COLD) that the manufacturer knows will work safely with the particular tire as manufactured, in all load conditions, derived from hours and hours and miles upon miles of testing. From this, I subtract 10-15% for the unladen condition of my car (usually just me). I've learned this provides enough pressure to insure good traction and even wear across the tire. So, for a 50 PSI Max, I would inflate to 42-45 PSI. 40 PSI Max = 34-36 PSI, etc.

A car manufacturer has no earthly idea what tires you will install on your car. Back in my youth, we used to inflate rear drag slicks to 16-20 PSI. You won't find that printed on any fuel flap. And you will never find tire pressure printed on the frame of a bicycle, or motorcycle.

pierrejoliat

Yes, I thought I knew better than all the Mercedes engineers as well, I ran 32 psi for three or four years, until I hit a chuckhole on two separate occasions and bent two rims, since I can't say if I would have bent that rim at 36 psi or not, I just decided to hedge my bet and run 36 psi and luckily haven't bent one since.

Would or does it matter? you be the judge.

Fliplegend

Regardless of what the door sticker says, I've pretty much ran 34-36 psi on all of my cars.

DFWdude

I used to think that, too, until I started running into OEM tires with a great deal more pressure. The Pirelli P6s that came on my C320 were rated 50PSI on the sidewall, and 34-36psi I used initially was well underinflated, wearing each shoulder tread in short order. I bumped them to 45psi and the wear evened out across the tread.

Not to mention that the gas flap says (to this day) 28-32psi... nowhere near the PSI ranges on the P6s delivered with the car as new. I would have burned through those P6s in less than 10,000 miles if I adopted the gas flap note.

Bhopkins

I have always used a similar logic, but opposite. My thought has always been that the tire manufacturers have only a general idea which cars their tires may be going on. The tire manufacturer's label is only a safety/liability maximum pressure statement. The car manufacturer has a greater understanding of the weight of the car, wheelbase, suspension tuning, etc.

BenzV12

I was running MAX COLD on the label just following the Mercedes-Benz not the tire manufacturer's .However, I had an uneven tire wear out in the rears and I was told that my tire pressures were higher than normal .
DFWdude is what I would recommend as well

S-Prihadi

I reference my tire pressure to my activity and the brand/type of the tire too.

Michelin Pilost Sport 4 : If I am in the city 32 front 33 psi rear is my usual. If I do long distance run and has 3-4 total person + luggage, I usually set 34 front ,max 36 psi rear.
When I bent my BBS wheel and while waiting for its arrival, I use on my original AMG wheels with GT Radial Champiro SX2 I have zero experience with, I need to 34/34 psi to have better sidewall firmness Mic PS4 offered at 32psi.

In the long run, if your front tire worn out well and the tire gave you the feel/response you want in terms of comfort and agility if spirited driving .... at your choosen pressure ( surely 30> psi ), that is what matter most.
The rear tires surely can't wear-out as well as front tire at its pre-set camber.

nightspd

If you don't mine me asking @DFWdude , what tires and pressure are you running these days?

degeja

I carefully checked wear with a tire measurement tool and wear for first 10000 miles-- with 2 people and empty trunk--- tires wore in midlle for first few thousand miles. Finally settled on 31 psi for all 4 tores. I use tire label pressures when loading car in trunk and people in back seat.

The door label makes sense when car is fully loaded.

DFWdude

I have a mixed set of tires at present... When I bought the car off-lease in Mar, 2018, all four Continental ContiProContacts had different tread depths... The MB dealer had replaced 3 tires at different times for the previous owner, without regard to having similar tire treads on the same axle. So much for replacing tires in pairs.

In late 2019, I moved the less-worn Contis to the front axle (still slightly miss-matched tread depths), and added two brand new tires on the rear. All sizes 245/40x18.

Front: Continental ContiProContact... MAX pressure molded on tirewall: 51psi I inflate these to 36psi cold -- well under my advocated 42-43psi -- to wear them out sooner rather than later... so when I replace them, the new tires will be closer to matching the tread depth on the keepers at the rear. It's working, as the shoulders on both tires are 2/32" less than the centers. I need to bump these to 40psi or so if I want to get the most mileage from them. Probably won't.

Rear: Yokohama AVID Ascent GT... MAX pressure molded on the tirewall: 50psi. I inflate these to 38psi cold. Only 2/32" of treadwear since new (18,000 miles), a little more on the shoulders again. So I need to bump the pressure to 41-42psi. I really like Yokohama tires.

Average number of potholes here in Texas, but so far, no bent rims in 4 years (knock on wood). Due to the pressures? I don't know.

As I get older, I like the slightly softer ride, even though the pressures are well above the 32psi printed on the gas flap. After an hour at interstate speeds, the pressures rise 3psi, still well under the MAX tirewall pressure, even with a full trunk.

juanmor40

My understanding of the side wall MAX is a safety label, nothing to do with ride quality, nor tire durability. As long as the ride is safe, and comfortable to your driving habits, that is the correct pressure.
Do those settings reduce mileage on the tires? That is a conversation between your wallet and your brain. Reduce comfort and pleasure to safe a few bucks is your car, and nobody else's. The values suggested in the door label are a good start to tune it to your likes.

I set mine at 35 front, 36 rear, and I like the ride from 30->120mph. Done 39 by mistake after tire rotation , and the car was bouncing all over the place after 90mph. Not my cup of tea at those speeds

You can monitor your tire pressures in the cluster as you drive. I usually see around 3 or 4 psu higher than cold settings as they warm up. If your start cold @40 you will be driving 43/44 when hot, i.e. four basketballs

Left Coast Geek

The MAX pressure on the sidewall is for the MAXIMUM LOAD RATING on the same sidewall. The car manufacturers specified tire pressures are for the vehicles actual load front and rear with 2-up and full load conditions given the stock tire size. the front usually doesn't change much (engine, being the main load in front) while the rear axle takes the brunt of the difference between light and full.

there are tables that give various tire sizes and pressures at various loads. For a given size tire, these are the same regardless of tire make/model, the difference between tire models is their MAX pressure and therefore MAX load.

CaliBenzDriver

The tire types and pressure depend on many options: size, weight, trim, AWD...

My car is a comfort trim ... not sport
all 4 identical... non-staggered tires
​​​​​​RWD only ... not 4M AWD
M276 modest power... not TT V8

I ride 35/40 with Michelins 245/45/17 Pri.MXM4Tall sidewalls are a bit softer than a sport shorter sidewalls.

I figured this these pressures by increasing 1psi at the time until I eliminated all "chewing-gum looseness" from both axles.

The funny thing is the rear wheels are really what is keeping the car going straight, not really the front wheels... If the rear is soft, the car gets sloppy all over. We have no control over the rear other than pressure. I find that keeping my RWD stiffer is what I like.
When over inflated you may get a bit of "basketball bounces" at Hwy speed, then simply back down 2 or 3psi, always referenced cold. Softness/hardness depends of many factors that's why you learn the handles to desired results.

For my setup: 35/40 and not equals (40/40) is to let the rear wheels win over the fronts! Try the opposite (40/35) you'll see the difference in handling...
play around and test drive 'till you get the pressure you like.

Left Coast Geek

FWIW, my wife's 2016 wagon says 35 front, 41 rear for 'normal' load, and 48 rear for maximum load.

CaliBenzDriver

OMG... 48psi, scary my sidewalls read Max:50Psi

Yeah, they've got lots of numbers in the owners manual, at door frame, at gas trap, on the tires themselves... all dissimilar numbers thus a bit overwhelming to understand at first


driver door sticker


gas trap sticker

Being a RWD only vehicle I was fascinated to realize the work difference between the Left vs. Right wheel. My right heats up about 2x more than left.
I guess my rear differential is the ultra-basic type that mostly work one single wheel. A fancier LSD would have been a bit more serious...

Left Coast Geek

2016 E350 4matic wagon...

gas cap:


door frame:

juanmor40

which reminded me that the sticker is for speeds @100 MPH, , and there is usually 2 passengers on mine; otherwise, nothing above 80MPH

CaliBenzDriver

Good point Juan, if we decipher the meaning of this sticker: a single driver in the US should inflate at 30/32 Psi an extremely low "recommended pressure"

Even a small Honda Civic needs higher minimum pressure to save gas

Arrie

Every tire model/make has its own “right” pressure to use. Tires are different and the difference mostly comes from the side wall stiffness/strength so some tires require higher pressure for even wear across the width of the tire.

Left Coast Geek

I completely disagree with this. a stronger sidewall enables a higher max pressure, but its the PRESSURE that holds the car up, not the sidewall, the sidewall just holds the pressure in. at the same pressure, the same tire size will have the same load rating. a tire with a higher max pressure will have a higher load rating simply because it can hold more air to support that greater weight.

let the air out, and the vehicle sits on its rims no matter HOW stiff those sidewalls are.

Arrie

And they make Run Flat tires too...

You are so wrong with this you have no glue...

Left Coast Geek

A run flat is a whole other thing, but when they don't have pressure in them, you can only drive a rather short distance rather slowly... And for normal use, they need the same pressure as any other tire that size with the same load.

juanmor40

https://www.tirerack.com/tires/tiret....jsp?techid=21

https://coopertire.com/en-us/tire-ed.../tire-pressure

As long as I have the pressures within safety limits of the manufacturer, i.e. not underinflated (damage to side walls), or overinflated (above max pressure), the tire pressure I set is around the car manufacturer's recommendation that gives me the ride I like: cornering, stopping distance, and reasonable comfort. I do not worry about extending the life of the tire, just buy another set as needed. I rather replace 4 tires than renew the suspension or replace damaged wheels.
What is the point of driving these cars under someone else's specification (as long as not violating anyone else's rights)? Right?