94 E420

I was just wondering what would be the correct tire PSI for my car with my current tires? 215/45YR-17 Goodyear Eagle F1 GS-D3 XL

CDP

It doesn't tell you on the sidewall?

MTI

Usually the sidewall only gives the max pressure. Mercedes usually has the tire pressures labled on the fuel door or elsewhere on the body. If it's not there, a call to the tire shop should do it, since they're supposed to have the inflation info on hand.

AMG_Eric

i had some goof fill my z rated tires to 32 psi because he said that is what the manufacturer recommends. needless to say that person no longer works on my car. one should only go with the mbz recommend when u are running STOCK rims and tires. otherwise go with what the tire says on the sidewall. if you dont go with the sidewall you risk uneven wear which basically means you will be buying tires sooner.

MTI

How does the sidewall number know how much the car weighs? The number on the sidewall designates the maximum psi the tire is designed for, not the optimum psi.

In the directions from AMG when fitting larger wheels to the W124, their recommendation is:

The tire inflation pressure is to be adjusted in
accordance with the production tire inflation
pressure plate in the gas tank flap.

AMG_Eric

i am sure that was the theory 15 years ago when 1) mbz didnt own them and 2 tires were not made the way they are now.

you must ask yourself when were "Z" rated tires made and to what specifications. also when did the rim sizes go above 17"?

just think for a second. if you put on lets say super low pressure tires on a 4wd truck and took it in the sand; however you exceeded the max pressure becuase you went with fords tire pressure then the tire blows. is it fords fault or the tire manu's fault?

an even better example would be you put large tires on your car (not stock) then you fill them to 32psi even though the tire says 55psi warm and you end up driving on the sidewalls. a tire is not meant to drive on the sidewall neither is it designed to drive with a cup in the middle of the tire.

basically what i am trying to say is dont inflate beyond a tires spec; however you must inflate it to compensate for tire wear.

the ntsb wrote this in regards to tire pressure
http://www.nhtsa.dot.gov/cars/rules/...ty.html#secV_A

so it begs the ? of what do you do when u install 20's on your benz when mbz doesnt recommend 20's?

MTI

Being quite famiilar with NHTSA's regs . . . . and the regs verify this, the number on the tire is the MAXimum psi, not the optimum for the specific vehicle. The number is a warning regarding overinflation, so your comment about going by the number on the sidewall made no sense whatsoever.

Therefore, the best action by the consumer is to check with the tire retailer, who should maintain the proper inflation data for either specific cars or axle weight.

AMG_Eric

fat chance of a tire guy knowing whats up. :P in fact the guys that sold me my first set of z rated tires said go with the 32psi. that is why i am kinda bitter. i had nice worn tires with the center of the tire being somewhat perfect.

in a perfect world a tire guy would know how much psi based on pure gvw (gross vehicle weight). however i have no idea where you could get that perfect information.

Kestas

After trying to keep tires at their proper specified inflation for 30 years, I now simply put 35 psi in all tires. I do this for a number of reasons..... I have never experienced an overinflation pattern where the center is more worn that the edges, but I've always experienced edge wear.... the added pressure over recommended leaves a bit of room should a tire experience a small leak.... I can safely load the car without adjusting the pressure (who actually goes through that exercise anyhow?!!!).... plus I strongly believe the recommended pressures are intended for ride comfort and not for maximum handling and safety.

neanderthal

AMG
do you actually know more about tires than your tire guy? and to answer your question, if you overinflate your ford trucks 20 inch tires and go on the beach and the tire blows up IT'S YOUR FAULT!! if you underinflate the tire and it delaminates, again ITS YOUR FAULT

the inflation pressure listed on the sidewall of the tire is the maximum for that tire, not the recommended air pressure, as already stated. the air pressure is determined by the manufacturer of the vehicle as they will know what particular ride and handling characteristics they will want the car to exhibit. and, as stated prior, that tire can be used in multiple applications, in cars as light as 2500lbs to cars as heavy as 3500lbs, depending on size.

the recommended inflation pressure is listed in any one of several locations; the drivers door or door jamb, glovebox, center console lid, other doors or jambs, trunk lid, fuel cap etc etc etc. in our case its a sticker on the door jamb, and should also state the tire size.

in most of our cases the 124s had air pressure that was something like 29 front and 32 rear, with additional instructions in the fuel cap to add 3 psi to the rears for max loads, or 3 psi to both for high speed, and that for constant high speed driving the max load capacity should be reduced.

that air pressure is for the factory size tires. if you change your tire size you should consult your tire sales person who can advise you what the approximate air pressure requirements are for your new size. most shops will just use 30 or 32 psi as that falls into the range for most vehicles.
however there is a chart available that will show how much load capacity a tire of "x" size will have at "y" pressure. you never want to have a tire that has less load capacity than the OEM recommended size, and whatever inflation pressure you use should meet the load capacity for the standard tires at the standard air pressure or exceed it, yet not exceed the sidewall maximum.

the load capacity of the tires is determined by the size, as the air in the tire is what actually carries the weight of the vehicle. so if the volume of the tire you are installing is less than the volume of the tire youre replacing, it figures that you need to increase the pressure in the tires to maintain the same load capacity. so in going from a 195/65-15 to a 215/45-17, one may have to increase air pressure by a few pounds. i just called a buddy of mine at costco but he's busy and can't look it up for me right now.

thats y'all lesson in tires for today.

i run 35 psi in both front and rear tires, as higher pressures generally yeild fuel economy increases (slight) and can improve cornering response, but at the cost of accelerated treadwear.

AMG_Eric

hey neanderthal if u reread everything i think you agreed with what i said.

Wadster

There are almost as many myths regarding tire inflation as there are about octane levels. But just to verify what is actually marked on the side of tires, I just went to the garage to read the sidewalls of a few tire brands.

On the side of a Potenza RE950 in 215/55 16" it states "Do not exceed 40 PSI to seat the bead" and "maximum pressure at max vehicle load 44 PSI." These are mounted on a '99 C280 with the fronts inflated to 29.5 PSI.

A different set of RE950's in 205/60 15" lists a maximum of 44 PSI.

A Firestone Firehawk in 195/65 15" lists a maximum of 35 PSI.

And last but not least, a set of Pirelli Winter Sport 210's in 205/55 16" lists a maximum of 44 PSI.

All PSI ratings listed are maximum inflation. In the case of the Potenza's, it even states that the maximum is only to be used to seat the bead. What's the answer to the original question? Unless the tires are the OEM size for that vehicle, there really is no correct answer. Once you deviate from that OEM size, the numbers listed in the gas tank lid now serves only as a guideline or a close starting point.

To AMG Eric:

Since you recommend inflating to the pressure listed on tires, what pressures are you running for your tires? What brand and size are your tires? And what are the manufacturer's recommended inflation listed for your car?

AMG_Eric

i think i said there is no real way to figure this all out. that is unless your tire and rim are within manu specs.

i run 40 psi - 45 psi all the way around. the tires say max psi 45. i have sumitomo htrz II's. they are 245 ?? / 17. i dont know the height because they are in TJ with my car being painted.

my buddy ran over the recommend on his mudders when he was pulling his big *** trailer and nothing happend. no blown or weird uneven wearing.

i personally have only had bad luck with under inflation. i have never blown a tire due to psi. i have only lost tires due to wear.

ksing44

I think Luke at Tirerack is the best source of information for anything related to tires. Luke has repeatedly said, "follow the recommendation of the car manufacturer since the tire company doesn't even know what type of car they will be put on when the build a tire".

Luke always says

I did notice that the "Sport" versions of some of the newer E-class cars have recommendations to use slightly more pressure than what is listed for our standard W124s. I asked Luke about it and he explained that "slightly" higher pressures could be used to customize the handling characteristics for your preferences. For example, you could certainly use the high-speed pressures to give your car a sportier feel when cornering. I use pressures close to the minimum, because I have always preferred the more comfortable supple feeling of a softer tire. I tend to add just 1 or 2 pounds above the minimum, just to be sure I am never below the recommended pressure.

Wadster

What??? You say that there's no real way to figure all this out yet you personally recommend running at or near the tire's maximum pressure.

I'd argue that there is a way to find out; it's called trial and error and you start at the automobile's recommended pressure. Adjust upward or downward to suit your preference and take care to note tire noises, changes in handling characteristics, fuel economy, and tire wear.

So how does your car ride with 40 to 45 PSI?

If I ran 40 PSI in my Potenza's, that would make for quite a bone jarring ride with a lot of harsh feedback through the steering column. And I'd probably hydroplane like crazy in the rain.

neanderthal

au contriare, i did not agree with you in anything i said beyond the manufacturers rec air pressure..

you said run near the use only the manufacturers specs for spec tires, which no-one here has argued, but you also suggest using what the tire sidewall says (4th reply in this thread.) you said if you dont you risk accelerated wear.

if you over inflate your tires you accelerate thier wear. if they are slightly underinflated you dont. you driving habits are the biggest factor in tire wear. so you can run the proper inflation all day, but as long as you think youre mario andretti, youre going to wear out your tires quickly.

you called tire guys goofs, said fat chance of them knowing what theyre talking about. well, goofs though they maybe, they still know more about tires than you do.

spec charts and inflation tabled have been around for years. z rated tires have been around for many years. 17 inch wheels have been around for years. they have only recently become common, which is something else altogether.

YNVDIZW124

Damn AMG_ERIC is always doing this! I guess he always wants to be right!

Anyways to get the correct tire pressure do what i do get your tires
dirty and drive on them to see where they are making contact to the pavement
and adjust the psi between the recommended tire pressure and the max to get less
tire wear and comfort in ride

too much air in your tires will cause harsh drving and give your tires heat
stress marks on your sidewalls

that'll be funny when amg_eric gets a blowout in his "ZRATED" tires for running them at 45psi!

I BET HE STILL GOING TO SAY IM WRONG!! AND HE HAS THE BEST ZRATED TIRES IN
THE WORLD!!DUDE YOU SOUND LIKE DONALD TRUMP

Wadster

I'm sensing a common theme here. But I'm also glad I wasn't the only one to notice the contradiction.

From time to time, I've heard of people hyper-inflating their tires and it makes me wonder. Do they have any idea what happens to a tire's profile and contact patch as the pressure goes up? Riding on rock hard tires can't be comfortable even with a cushy suspension.

ksing44

I certainly don’t want to name anyone specifically, but there is certainly plenty of bad information available on the forums. Thankfully, however, there is also plenty of correct information from people that are experts or that are at least experienced about the issue on which they comment. I love these forums.

MTI

This is the "advice" that I initially objected to.

AMG_Eric

so basically if you have say 55 or above psi tires run them underinflated at 32psi because the sticker in your gas door says so. gotcha makes total sense. i mean why else would they put that on the side of the tire? its all good especially if it should be at 55 and ur at 32. heck then you are only under pressure the max pressure by 23psi. i guess if i exceed the speedlimit my car will blow up after all the sign says max speed 65mph.


if this really comes down to splitting hairs mbz didnt have z rated tires installed as OEM nor did they recommend them in 1993-94. so i must ask how the hell could your car go 150 mph on non-zrated tires??? my speedo goes past 150 so i must be able to do it...anyone....mti??? neanderthal? i guess critical thinking skills are not part of this discussion.

one of you says do what the manu says. one of you says do what the regs say. i still bring up the point of low pressure rock crawler tires or off-road tires. they have max psi's that are quite low. if you go by the manu then its 32psi...boom there goes the tire. if u use the "if u blow the tire its your fault" that is kinda lame because it violates what you said b4 that the manu is correct. now i would agree if you blow your tires due to over inflation is your fault if your logic allowed for it. all NEW tires now have loading indexs that tell you what they can and cant go on. back in the early 90's the load indexes were not there.

here is bfg's tire specs for their desert tires. NOITCE THE PSI ratings for the same tires with different loads. do you honestly think that ford ever intended these tires to be put on a f-150? if they did does the 32 psi in the gas door apply?

http://www.bfgoodrichtires.com/assets/pdf/baja_ta.pdf
here is a great link. http://www.1010tires.com/tech.asp?type=tires it says exactly what you guys are saying but it is ignoring the fact that different wheel and tire sizes can be installed on a car even if they are NOT recommended. also notice the picture of inflation. the reason i have more air in my tires is they freaking cup if i dont run them close to the max. also notice it says i have had 0 problems in the 23 years i have been driving. maybe i am on crack cocaine but it works for me. i dont run stock rims or tires. the information clearly states run what the manu recommends. MBZ never recommended 17inch rims with 40 series tires let alone 18s so what do you do? i saw someone say go with the tire installer. well the morons at american tire/ tire.com just said go with 32psi and i ended up cupping a whole set of tires. i guess they were correct because it must of been my imagination that the tires cupped just like the illustration in the link i provided above.

honestly do what ever you like. its your money. you buy your tires i dont. i merely tired to give my POV. i have bought countless sets of tires for race trucks, mbz's, american cars and jap cars. i am not a tire person by trade but i do run the psi in the filler door when i run STOCK tires. however all bets are off when it comes to say 17" rims with 37" tires.

for you all concerned about my over inflated tires they are happy and inflated and ready to do some 120mph sprints if you would like a ride in the passenger seat.

Wadster

Eric,

Are you simply not reading the replies or what??? At least two others besides myself have stated that the pressure listed in the filler cap should serve as a rough starting point for pressure especially when deviating from the OEM wheel size. Did I say that 32 PSI was an absolute pressure that must be adhered to? No.

While you've posted some wonderful facts and figures on speed rating, I have to ask WTF has it got to do with inflation pressure??? Especially the DESERT tires!!! Nothing like digging up unrelated stats to prove your point.

And you still haven't answered my question to you; How does your car ride with 40-45 PSI?

I'm doubtful you'll answer the next questions but I'll post it anyway:

1. Given a base starting pressure, what is the effect of increasing the tire pressure, i.e. how does it affect performance and handling?

2. Given a base starting pressure, how is performance and handling affecting by decreasing pressure?

Even if you don't know the exact pressure for a given tire and axle weight, you should at least know the net effect of increasing or decreasing pressure. Anyone experimenting with tire pressure with only the vague notion that it "decreases wear" is simply guessing.

Wadster

Oh my GOD. We're not ignoring it; we're not even arguing it. In fact, you're the only one arguing a point that no one has brought up. Of course you can vary the tire and wheel size. As long as you don't deviate too far from the offsets and overall tire diameter such that turning radius, wheel travel, or suspension geometry are affected, you're good to go.

Your question: Why would tire manufacturers stamp a MAX pressure on their tires? The answer is simple; if they didn't state a max, goofy bastages would fill them up like bicycle tires till they let go.

Eric, that max pressure is your safety margin. The fact that your overinflated tires haven't let go should serve as a testament to the manufacturers quality and not as a validation of your "opinion."

AMG_Eric

i clearly didnt mention your name wadster.

it goes to the arguement of what the manu recommened. the speed rating is listed as well as the size and pressure. and in order for the manu to recommend a tire it has to include all of the info not just 1 item. sorry it wasnt clear for you.

rides awesome. care to go around corners at high speed or indulge in some high speed braking?


wrong again my friend.

my main focus has been contact patch wear. i dont really care if i have a rought ride i have all amg suspension. if i cared about the mbz feel i would go stock with stock tires and rims. having said that i dont experiment with 2-4 psi at time. 1st i check to see if its cupping over time. i always buy the same tire now that i have found one that wears to my liking and sticks to the ground. these are great tires in both wet and dry conditions.

to answer the ? about handling and performance, if they are inflated to 32 psi the steering is slugish and slighly unresponsive. additionally braking just blows because my contact patch is not at its optimal level. if i run 32 psi i also get massive wear on my sidewalls as i love to corner harshly. in the past i also had probs with potholes and rim cuts with low psi with this brand of tire. keep in mind i have 4 piston caliper brakes with slotted rotors. my tires never brake lose unless i am underinflated or if i do burnout or basically go on a fishtale whim.

i did this all along time ago. i have owned this car for 9 years. what i run now is based on pure experience. i have run many different brands of tires and different tires sizes. at the moment this is what works for me. now that my car will be back from paint tommorrow i may change everything becaue i had the fenders rolled.

after 9 years and at least 10 sets of tires i KNOW what is right for my application. if there was a perfect forumla i would use it. alas one can not be had with all the diff suspension setups. cars, vehicle weights, rims sizes and tire sizes. i am speaking purely from my experience.

if you like i can talk with my pit crew cheif and ask him to give me a long diatribe about what he does and doesnt do with tires.

AMG_Eric

seriously you need a different hobby. why would a tire company bother placing a max pressure on a tire if just about every manu that sells cars in america uses 32psi as a standard? wouldnt it be more simple for the tire company to just put 32psi since that seems to be the psi of choice by manus? additionally that would make a HUGE safety margin for them.

let's do this. you find me at lest 10 manus in the 1990's that recommended pressures beyond 32 psi and i will gladly call it a day. because after all this is a discussion about cars built in 1993 and 1994 not 2005.