Substance

I picked up the car about 10 days ago, its a brand new car. Tire pressure monitor shows 42 psi for all 4 tires. Recommended values in the fuel tank door shows much lower ratings. It did come from the factory with 42 on each though. What is the correct pressure which i should set my tires to?

Note: I rarely drive above 80m/h. Generally 2 people(incl. Driver) with very light load. The car came with bridgestone run on flats.

thefisch

have you checked the values with a pressure gauge also just to be sure? Not doubting the system since mine is pretty accurate, but just to be sure I normally check with a gauge. The tpms system on my car has typically been within 0-1psi of a gauge reading so I rely on it in between manual readings.

btw, what values are shown on your fuel door? My 11 e550 with NRF 245/45R17 tires shows 33F/35R for normal load (which I set them to) and 36F/39R for max load on the fuel door. Driver b pillar sticker shows 36F/39R - manual says b pillar sticker shows max load, not normal. curious to see if that is different for a my14 runflat BT.

I recall from the days of owning a Prius there were many online forums where folks professed running tires at higher inflation for better mpg. I kept them at 40/42psi for a while but became concerned about excessive wear. After that, I kept them at 35psi and barely noticed a drop in mpg considering all the other variables.

Live Oak

"It did come from the factory with 42 on each though."

Don't be so sure of that. New cars generally have the tires checked/filled at the dealership; part of the published make-ready routine.

My E550 was delivered to me with 45 pounds in each tire, measured with gauge --- wildly out of spec. Some techs have strange ideas about what tire pressures should be.

thefisch

45! - that could be close to max pressure depending on the tire. What pressure do you run your E550 at?

I have even had tire shops set the pressure wrong on my cars. Assuming the replacement tire size is the same as OEM, you can always follow what is on the door sticker. Last time we got new tires for my wife's car they set the pressure to 38psi when it should have been 32psi per door sticker. I don't think those guys check that sticker.

Arrie

The correct tire pressure depends on the tires you have. The sticker pressure RECOMMENDATIONS are for tires MB tested their cars on and my guess is they used Continental as their primary tire so if you have Contis on go with the stickers on the car. Not the one on the fuel door, the one on the door jamb.

As an example of pressure difference I had a set of Firestone Wide Oval tires and used 36 psi in front and rear. Tires wore thin in the middle of the thread.

I have Nokian zLine tires now. I emailed the manufacturer for the pressures and they told me 40 psi on all tires with minimum load as that is what I have in my car. Just checked the thread dept two days ago and the tires front and back wear very evenly across the tread.

With the 40 psi the Firestones would have worn to the wire in the middle of the tread.

Substance

They are bridgestone run on flats. I special ordered my car so I am pretty sure it came with bridgestones from the factory.

Fuel door says 35 for cold for under 100mph. Add +4 for warm. I will check the door sticker later.

Should i contact bridge stone or mercedes for correct values?

thefisch

MB will tell you to follow the driver door placard and what's on the fuel door - same thing the owner's manual tells you. Are they the same values on the placard - 35psi for front and rear?

According to the Bridgestone FAQ on their website, they are telling you the same thing:

Run-Flat Tires (RFTS)

What is the recommended inflation pressure for RFT tires? Follow your vehicle manufacturer’s recommendation for inflation pressure settings as indicated on the vehicle tire information placard and/or in the vehicle owner’s manual. Like other tires, RFT tires need proper inflation pressure maintenance for safe operation and to achieve maxim¬um tire life and performance. Check inflation pressures monthly and before long trips or carrying extra weight. Use an accurate tire gauge and check pressures when the tires are cold. Tires are considered “cold” when the vehicle has been parked for three hours or more, or if the vehicle has been driven less than a mile (1.6 km) at moderate speed.

If you have further questions concerning Tire Pressure please contact Technical Services at 1-800-847-3272.
Even Tire Rack which sells a bunch of different brands tells you to follow what's on the placard.

Does this mean there is one perfect setting - not necessarily. You still need to monitor the wear of the tread like Arrie pointed out. When you get to a rotation interval, check the wear or ask the tech and make adjustments if needed if wear appears due to over or under inflation.

sigx5

I have 30 psi all around (cold temperature); 34 psi after tires warm up; never have an issue (bmw & mb).

thefisch

After more thought about it, I decided to increase my psi to the max load (~900lb) psi noted on the door placard of 36F/39R. The sticker on the fuel door indicates I could use 33F/35R for normal loads or 36F/39R for max loads, but I don't want to have to increase the psi whenever the whole family and some luggage is in the car. Seems silly to me. Also, the extra pressure is needed when I decide to take if above 100 mph

Not sure why the fuel door sticker on my car gives two options for normal and max load others report only one recommended psi like on the door placard for max load. Does anyone have insight into that? Perhaps because it is the luxury version and higher pressure means a slightly harsher ride.

sigx5

Cold - 36F/39R
Warm - 39 (or 40)F/ 43 (or 44)R

as long as you don's feel "a slightly harsher"...

thefisch

So we have the same recommended settings. Do you have a staggered setup or is it the same size on all 4 tires (like mine)? Interesting that some models have different recommended pressures depending on the axle while others are the same all around.

sigx5

No, sorry if I confused you
I have 30 all around, it is perfectly fine to me (even though 265/35/18 - Rear)

If you have PSI as -Cold - 36F/39R; after tires warm up, the PSI will be - 39 (or 40)F/ 43 (or 44)R.
To me, it is to harsh, not good for suspension (strut. joint...etc).

thefisch

Thanks for clarifying. What does MB recommend for your car? I realize you prefer to run at 30 psi, but just curious what they recommend.

sigx5

Normal - 33 F/ 35 R
Max - 35 F/ 42 R

I had 30 all round with my previous BMW e60 530 for 10 years (w/ Michelin PS2), no issue at all; current 14 w212 E350, I use the same setup, happy with it (in South Cal).
Again, this is my personal preference "ONLY"; if you are not sure, go with Mfg suggested PSI, best and safest way to go.

Note,
I check PSI regularly (every two - Three weeks, have air compressor in the garage).

thefisch

Thanks for sharing. I may lower the pressure back down to 33/35 or midway between the norm and max load recommendations, especially if I find it too harsh or have to adjust for wear issues.

I still find it odd that they give two recommendations (norm and max) for some cars, but not all, and that they vary it by axle on some cars and not others.

Trancebolt

Ive been long pondering and playing with the tire pressure and the tpms on my mercedes'.

Today i went and bought a regular cheap tire pressure gauge to let out air, and a digital gauge that was expensive to actually read it.

Car is a e350 w212 2012 bluetec, and the tires came from a dealer at 39/41 ish. Not even equal on each side front or rear... like 38/39, 40/41, and fluctuating at speed/temp.

The measurement on the dash display always bothered me. Using the hand gauges, the reading was totally different from the tpms display. It was readiing 36.5/37.8 on front/back....After releasing a bit of pressure down to what you gents are saying for a 350 (35.5,36). Only drove 1 mile since i lowered the pressure but the roads are nasty enough that i got a potentially smoother feel. I have goodyear eagle runflats on my car.

Why would a car thats not staggered and on 17 inches, or any car setup using the same four tires on all side have uneven tire pressure front/back. Just seems against logic. I was concerned about the suspension/front shock/front strut as well as some other gentlemen here noted; when the PSI was higher. I have a feeling my drive home today will yield more results, however...

Turns out the TPMS rounds up. Anytime its x.5 or over, it rounds up the PSI. So my car was saying 36/37, when the digital gauge showed 35.5/36.1. Also the TPMS catches up to changes slowly.

El Cid

Regardless of the tire brand, MB recommendations are for ALL tires used on the cars. They will frequently change brands during production, so TP's are not specific to a brand but to the car itself.
check out the Operator's Manual and compare it to the placard. May also be a sticker on the "B" pillar, driver's side of your car. The OM will give more specifics on determining which TP is best for your driving.
I check mine with a gauge every couple of months when tires are cold. I run them about 2 lbs. over recommended and appear to be wearing evenly.

DerekACS

How difficult is it for owners to read the printed label found inside of the fuel filler door ?
This label gives tire pressures for front & rear, normal load and heavy load. It is very easy to understand, but maybe not for some ?

Trancebolt

Personally, my experience is telling me that runflats do not require the recommended tire pressure of the car. Their nature of being able to run empty and having a stiff sidewall continually makes me think the lower I get, closer to 32, the better feeling I get from the ride. Other drivers as well have commented on the factory 40 psi yielding terrible ride and bounce with runflats




The fuel filler door and b pillar suggestions are so played out. If we needed another reminder that its posted with three different numbers on every car we wouldn't have found our way to this forum.


Truth be told, despite the people refusing the delve deeper into this issue, many people including my own personal observations can state: tire pressure recommendations CANNOT POSSIBLY be universalized, and every change ive made away from the recorded numbers has only been positive.


Not every driver wishes to only maximize amount of tire life. That's a small portion of what tires do for me. 25000 vs 50000 miles is a tradeoff in someway shape or form. Wearing evenly is a good thing to see, but with the default factory pressure mine is wearing more in the center; neither here nor there. My goal is not in any way to maximize tire life, so those of you that have that goal, may look no further than the flap.


However, If I can give up 5k-10k miles of life off my tires to GREATLY improve handling, grip and ride comfort (or any of those three depending on the person) then it is worth it to continue this debate.

El Cid

If tires are wearing more in center, it means you have either too high or too low a TP in them. Not sure which. This means your tires are not only wearing out too early, you have less traction because mostly the center is touching the road. This affects handling and safety and MPG.
I check the depth of mine with the quarter method and adjust TP if needed. Generally have run 2 lbs. over recommended with great success. This may cause a slightly less comfortable ride, but improves handling, tire wear and MPG.
Also, I use a hand pump to add air to mine. If down only a few lbs., works great. I do this with three vehicles about every 2-3 months.

El Cid

The fuel door, "B" pillar and Operator's Manual for my 2010 had multiple different recommendations. There were two in fuel door. One stated for loaded, but the OM said that one was for driving 100 MPH!