frankj9000

Any idea on what correct tire pressure should be?

I have a 2017 e300 sedan, sport, with 19" AMG Rims, and 245/40R19 Continental Pro Contact Gx SSR MOE tires.

The b pillar shows 37 psi front 43 psi rear for those tires. The fuel filler cap shows 33 psi all around. The owners manual says look at the b pillar and fuel filler cap.

The car came from the dealer 35 front 37 rear. Called the dealer, no clue.

Any help would be great.

Thanks

shortspark

I owned a 2012 MB ML350 4-matic. I currently own a 2017 CLS550 so although I do not have the E class, I have struggled with this question for a long time and it periodically comes up at this forum. You are right, dealers don't have a clue - go to one and you get an answer, go to another and you get a different answer.

Here is the bottom line. For normal, general purpose driving use the gas filler cap recommended psi. For autobahn type driving (fast and long) or heavy load or towing, use the psi on the pillar. Having said that, you may want to adjust a pound or two for size and type of tire and/or individual ride and comfort.

Here is an article that explains it better: http://www.tirerack.com/tires/tirete....jsp?techid=72

c4004matic

This seems to be a constant issue with MB, inconsistent labeling of tire pressure. One is the European version the other the US version. The fact is one is for high speed use (higher pressure) the other for low speed. If you want the most comfort and never drive over 100mph use the lower recommended one. If you don't mind a little more stiffness and drive a little more enthusiastically use the higher pressures. Your choice! I use the higher pressure on my summer tires and the lower one on my winter set. Another consideration is your wheels, 19's and 20's should always be inflated to the higher pressure for them to function appropriately, not only does this allow the tire to perform its best it also protects the wheel from damage.

frankj9000

Many thanks. First mercedes, always had BMW, They judt lust USA pressure reccommendations.

NOMRW8NG

Here's a link to a table where you can figure out what pressure to use if you change wheel or tire size from what's on car's label.

http://static1.1.sqspcdn.com/static/...+inflation.pdf

You can see from this table that the lower profile tires do need to be run at higher pressure in order to carry the load.

thefisch

Go with gas cap flap pressures for normal driving. Door placard pressure is for max load which is sometimes, not always, also listed on gas cap flap.

jadatis

Tirepressure-advice is all about to give the tire a deflection that wont give to much heat at any spot of the rubber of tire.
For that load on tire and speed is important.

On the car is advice that high that its impossible to be to low pressure in any condition people are able to use the car, for responcibility reasons .

In the book of car is a more reasonable advice .

I am able to calculate it for you if you give 100% acurate determined loads on seperate tires , and maximum speed you wont go over for even a minute.
This is impossible , so we always have to use as much possible reserve.

To much reserve though gives that less deflection that comfort and gripp get unaceptable, so we have to find the right balance .

But to low pressure gives tiredamage , and can cource in the short or long run blowing tire and accidents with the missery that goes with it.
And so pressure should never be to low, better to high with discomfort then to low with chanche on accident.

Greatings from a Pigheaded Dutch Selfdeclared Tirepressure-Specialist.
Peter

Dashoto

Just to echo a lot of whats been said already, there are several combinations of tire pressure suitable based on your max speed and your max cargo load. The B pillar, from what I understand, is suitable for max vehicle speed and max vehicle cargo load (5 passengers and trunk full of luggage). The back tires are higher pressure to accommodate three large adults in the back seat with a hundred plus pounds of luggage in the truck.

For my everyday driving in the US with very little cargo and at max 2 passengers 99% of the time, the gas cap is sufficient for the best ride according to Mercedes. But I go 35 / 35 to make sure at cold the tires do not rest below 33 / 33

mercnewbie2

Hey guys, I been reading about PSIs for over an hour and I'm still confused. I have 19" Pirelli run flats on my 2017 E300. The gas cap says 32 psi front and back, but is that for run flats? I'm always at normal load and speed, so I just want the "default" settings for most comfort. I read another post that said run flats run better with higher PSI. Do you agree with this? They came from the dealership (CPO, put on new tires) at like 38 psi, but not sure if I should go higher or lower.

JTK44

Just my $.02:

I use the gas tank pressure plus 10%: 33/33 normal load: 35/40 maximum load: I have stock 18 inch wheels on my E450. Most of my driving is myself or with my wife, or myself and my ski gear so I am always less than 5 people so I use 33/33 plus 10% 36/36.

I find that 10% plus, at cold, i.e., sitting overnight, gives me better handling, better fuel economy and the ride is still silky smooth.

Note that a drop or of even 10 degrees will change the tire pressure 2 or 3 lbs. So in the fall and winter I have to add air to keep the pressure at 36/36.

I have air compressor at home and a digital tire gauge. BTW, the pressure reading on the information screen is withing one pound of my digital gauge which confirms it is accurate.

mercnewbie2

That's helpful, thanks. And to confirm, you're talking about stock run flats? And are 19" wheels typically filled to higher PSI than 18" or is that not a thing?

JTK44

Yes I have stock 18 inch wheels with Pirelli 7 run flat tires.

Do not know about whether or not 19 inch wheels need higher pressure.

What does the recommended pressure on the fuel tank say - more or less than what it says on my car with 18 inch wheels?

Use that as a guide.

ua549

I use the recommended tire pressures of 33 psi cold. After driving a mile to the grocery, the tire pressure is 40 psi with tire temps near 120° F.

smoldr

My dealer said to go with the fuel filler specs

DFWdude

No car manufacturer can anticipate what tire you mount on their cars. So, the numbers printed on the fuel filler door are just suggestions, assuming the most likely range of tire you will use.

I examine the sidewall of the actual tire. It will have the maximum, fully loaded pressure recommended for the tire from the tire manufacturer. Whatever that value is, I subtract 10-15% and fill to that pressure.

rraisley

Uh, they kinda can. It's specified as a 245/40R19 XL load rated. Which is 1653 max pounds per tire. For tires I've checked max pressure is 50 or 51 pounds. I'd say use their recommendation, possibly a bit more as others have said.
Assuming 50 pounds less 10-15% and you get 42-45 psi. I would /not/ go with that.

DFWdude

If the tire is rated 51psi max (cold), and you inflate it to just 32psi (as specified on the gas flap) your tires will wear out on the shoulders with tread remaining in the center. Hardly desirable. I observed the "gas flap" standard (28/32) with the Pirelli P6s that came with my C320. (52psi cold max) This wore down the shoulders in no time. At mid life, I upped the pressure, which evened out the wear, but the damage had already been done. I got barely 20,000 miles on that set before the shoulders went completely bald. A pity since they were nice tires.

The wider the tire, the more pressure is needed to keep the center tread inflated and even out the treadwear. This is not rocket science.

I've observed the tire sidewall PSI less 15% for many years, and I get the most even treadwear with zero problems. The ride is less dull... still smooth but more lively, I'd describe it. Better fuel mileage, too. YMMV

JTK44

Just my $.02:

Inflating to maximum 51 psi less 10 to 15% imo, may not be the most prudent thing to do. (personally I think it is a dumb idea)..

10% to 15% less than 51 psi would be 44 to 46 psi. Not only would the ride be rock hard your tires would wear unevenly: the center would wear out way before the sides. Your contact patch would also be diminished and in rain when braking that could be fatal. You also increase the risk of a blowout and bent rims.

Also in warm climates when you drive at high speed you can expect the pressure in your tire to go up by 6 to 8 psi. When that happens you would be exceeding the maximum psi on your tires which would be dangerous.

As I posted, I use the tire pressure recommended on the fuel flap, 33 psi (normal load) plus 10%, 36 psi. The ride is still silky smooth, the handling more precise and both tread wear and fuel economy are improved.

For detailed analysis about the dangers of over inflating tires see: https://blog.firestonecompleteautoca...ate-car-tires/

ncdoc

I believe the maximum pressure listed on the tire sidewall is a COLD pressure, so max - 10% would be fine though tire wear and comfort might not necessarily be best. My CLS 53 recommends a rear pressure of 47 PSI for full load/high speed which is quite close to the max cold pressure.

DFWdude

Thanks, ncdoc, for being curious enough to do some homework. Others just accept tradition or what they are told.

As noted previously, Tire Manufacturers know what is best for their tires... better than any car manufacturer. And Mercedes-Benz wants it's customers coddled in comfort, so a $1200 set of tires every 18-24 months is no consideration on an $80,000 car.

ua549

I keep tire temperature and pressure readings in the leftmost display panel. I use the MB recommended pressures. After driving 3 to 5 miles, the temperatures have increased by about 40° F and pressure is up more than 10 psi. It makes me wonder what the readings would be when driving at high speed for an extended period of time. I often run my BMW road car non-stop for > 400 miles but tire data isn't available.

JTK44

In the summer I start at 36 psi. After driving at high speed when outside temperature is above 85/90 the psi as per the gauge will be about 41/42 with temperature about 115 degrees.

That is why I posted that starting with 44/46 psi would be dangerous.

DFWdude

Let's try this again... after driving on the Interstate at 70mph for 1/2 hour, my "dangerous" tires read 44-46psi HOT, well under the recommended maximum COLD tire pressure that the tire manufacturer notes on the sidewall.

I've put 9,000 miles on some new Conti Contacts, and the treadwear depth measurements are identical -- groove to groove -- across the entire tread patch. You will NOT get that on Contis inflated only to 32psi cold. Take it to the bank.

Most MB "owners" don't care, because they will return their "rented" car after 2 years, only to be zapped the cost of new tires because the old set wore unevenly.

JTK44

Last post to DFWDUDE:

If you start at 44/46 psi cold (10% to 15% less than max 51 psi) after driving an hour on the interstate when the ambient temperature is 85 degrees or higher, the temperature in the tires will be above 115 degrees and the psi will increase by 6 to 8 resulting in a psi above 51 the maximum. This will be dangerous.

Your ride at 44/46 psi will be rock hard, and the chances for a blowout or rim damage will be increased. At this high pressure there is little to no give in the sidewalls: hence the rock hard ride and increased potential for blowouts and rim damage.

But the real problem, regardless of what you say, is that your contact area at 44/46 psi will be diminished and in the rain when braking the results can be disastrous

I have an accurate tire gauge and periodically check my tires for wear: at 36 psi my tires, front and back wear evenly, across the tread and I usually get between 35,000 and 40,000 miles tread life.

ncdoc

JTK44: How can you explain that MB recommends a cold tire pressure of 47 PSI in the rear on my CLS53 for high speed driving? You can argue about tire wear and ride comfort, but it is not a safety issue if cold pressure is kept below the max pressure.