edspider

I noticed (after 3000 miles) that my dealer inflated all tires to 33 pounds, but the door suggests 28 pounds for the front. Anyone know why MB recommends less in the front? Is it ride, performance, mpg?

paulv

All the above reasons you stated, and probably a few more. Inside my gas fill flap there are pressure recommendations for up to 100mph and 100+ mph.

Regards,
paul...

edspider

Thanks Paul, but which direction does higher pressure lean. I'm going to assume it would mean a stiffer ride and better mpg. Does it also mean better handling? If this is the case, why would MB recommend lower pressure? Longer tread life? Softer ride?

Barry45RPM

The guy filling you tire with air is NOT an engineer as was the guy who directed the tire pressures and tire pressure placard be placed in the gas filler door. With all due respect to the tire filler's skills and experience, it is definitely not up to the levels of the people who designed your car. He is second guessing them, or too lazy to remember the different pressures on each model & 33 is not an unreasonable number for almost any car...

(As the air conditioning school comercials say on late night TV... "You have to be an engineer to design one of these roof top units, but you DON'T have to be one to keep them running in top notch condition... Call us now...")

Overinflation usually means MORE tire wear (in the center of the tread) & harsher, not "better" handling. It also leads to less traction in wet weather. Remember, the front tires turn AND lean in & out, and lead the car, not follow... Why guess? An engineer told you what to inflate your tires to.

paulv

Considering all the variables in this "tire pressure" equation, it's difficult to say what exactly will happen when someone doesn't follow the recommendations.

It's common knowledge that increased tire pressure will cause a harder ride and will yield "some" better gas mileage and will cause some handling differences (my experiences have been less traction around turns at higher speeds) as you already mentioned.

Since I'm not an expert, here's a link to TireRack with some good info on tire pressure related stuff:

http://www.tirerack.com/tires/tirete...e.jsp?techid=1

Regards,
paul.....

vettdvr

So perhaps this is why my E500 placard has 25 psi front 32 rear. Maybe the front is so much lighter than the rear or at 150 mph the front end becomes lighter. But 25psi still seems soft. Jim

MB-BOB

Then why does the placard on the door seal of every E320, E350, E500, E55 AMG (etc.) say the same inflation values, whether you have stock touring tires, lower profile tires, or performance rated tires on the AMG models? Indeed the placard is a standard part slapped on every car in the model range, no more "engineered" for the tires on the car than the man in the moon.

Look at the tire pressure ratings on the sidewall of your tires. If it says Max of 44lbs psi, why on Earth would you rigidly follow the door placard recommendation of 28psi? The OEM tires on my C-Class were 51 psi Pirellis, and I foolishly ran them at the placard recommended 32 psi, until the shoulder tread went bald at 18K miles (the center treads were almost new).

My replacement Dunlop SP Sport A2s (44psi sidewall rated) are kept at 40-42psi, and after 20K miles they are evenly worn across the tread, and front to rear too. The ride is no different than when less inflated, and they perform just as well, especially in the wet.

Finally, go to any dealer and inspect the tires on the various E-Classes. You find tires from Continental, Pirelli, Goodyear, Michelin, etc., and not a single one of them set to run at the same pressure. So what good is it for an engineer to recommend tire pressures on the b-pillar of the door, when the assembly line slaps on whatever tire Mercedes bought for the cheapest price?

Following the door placard is nothing more than urban myth. You should follow what the tire sidewall says. The engineers who designed the tire know better than Mercedes does what tire pressure works best with their tire.

Alan Smithee

Bob, are you joking?! Please tell me you are...because otherwise you are going to get people killed.

The pressure indicated on the side of a given tire is the MAXIMUM PRESSURE for the tire. IT HAS NOTHING TO DO WITH THE SAFE PRESSURE FOR THE CAR! That's where the manufacturer's recommendation comes in; the pressures recommended are the best compromise for safe handling, acceptable ride, and acceptable wear. Of course, everybody has a different driving style, and pressures can be adjusted accordingly. For instance, I drive in a spirited manner through canyons on a daily basis, and factory recommended pressures are generally too low (as indicated by excessive wear on the outer edges). My girlfriend's Porsche shows no wear on the outer 1.5" of the tire, however, so the factory recommended pressures are too high for her (mostly freeway) use.

MB (and most manufacturers) recommend lower pressures for the front tires to invoke understeer (that's when the front tires lose traction first at the vehicle's limit). Understeer is a much safer way to lose traction (and for most people, control) than oversteer (rear tires lose traction first), which can result in a spin.

Barry45RPM

The tire pressure range on the sidewall of a tire is the allowable range by the tire manufacturer who does not know what car the tires will be put on by the auto manufacturer. Those tires will fit on an almost endless list of cars. Those tires on OUR car are supposed to run at a specific inflation pressure to deliver the best balance between wear, handling & comfort on OUR cars. Other cars might require a different pressure within that tire manufacturers permitted range to deliver the best balance on that other car. The reccomended pressures by the 2 different auto manufacturers are for the sam tire on THEIR car.

The tire pressure range printed on the tire is not a "pick whatever inflation pressure you want" buffet for you. Bear in mind when E Class owners change the tires/rims on their car, the sticker is still inside the gas door, reccomending 28/33. Does that mean that that is the correct inflation pressure for the new set up? No, because the sticker doesn't know what tires are on your car... Just like the tires with the printed inflation range don't know what car they will be installed on.

The range is the low and high limits the tire manufacturer can stand behind his product at.

C'mon, you should know better.

MB-BOB

I sleep well at night, thanks. The broker who sold my Mercedes to me recommends tire pressures be maintained within 10% of the sidewall maximum pressure, and has kept this advice for decades. He's right.

You’re right, but for the wrong reason. It’s all about product liability.

For tire manufacturers, the (cold) sidewall maximum pressure on the tire is:

1) the maximum recommended for a FULLY LOADED car… When was the last time you had 5 people and 400lbs of luggage in your car? Or just two people only?

2) the line in the sand below which the tire manufacturer stands liable for its tire to the USDOT… There is a substantial margin above the maximum pressure in which any tire can safely operate (fully loaded), but beyond which the manufacturer will warrant the tire.

For Car manufacturers, tire pressure door pillar placards represent:

1) the safest recommendation that errs on the extremely conservative side, also for liability reasons. As Barry45RPM notes, they have no idea what tire you will place on the car once it leaves the factory (not to mention the variety of tires their own factories will place on the car), so the placard is the on-car documented limit they feel will not get them sued, understanding that most drivers are idiots regarding how their car works. That’s all it is, period.

2) guaranteed repeat business. I haven’t bought a tire at a dealer in many years, but the majority of drivers do. Underinflated tires is the best way to guarantee the car returns to the dealer for new ones, along with an opportunity to sell overdue maintenance, etc.

I'm not sure we are really disagreeing on much of this. But as we debate the finer points of this issue, please keep in mind several things:

1) The acceptance of low profile, 17” and 18” tires means an undeniable march to higher tire pressures. (Just take a look and the sidewall pressure ranges for these tires.) Tire pressure placards have not kept pace with this trend, as my first hand experience with the aforementioned Pirellis clearly attests.

BTW, as radial tires largely replaced bias-ply tires in the 1970's, the placards changed not one iota. In fact, they still haven't changed to this day.

2) The contact patch on the road is the most important variable in car safety. I’m sure we can all agree that as tires get wider and lower in profile, maintaining proper road contact is key. Underinflating tires because the placard says so decreases the contact patch (only the shoulder tread does the work). I assert that this trend decreases safety.

3) Professional drivers and we enthusiasts work from the tire…up. They look to the design and composition of the tire, and tune the car to the tire, not the other way around. Hence, I will ALWAYS be guided by what the tire sidewall says, over the one-size-fits-all DOGMA of a door pillar placard.

Finally, I haven’t mentioned on this forum (but on the W203) how I got 50,000 miles of spirited driving service from a set of Goodyear Eagle Gatorback 225/50 R16 tires on my previous car. The door pillar on which these OEM tires were mounted said 32/30. But the tire (delivered with the car) said 44psi. I kept the tires at 40-42psi all the time. By the time these tires wore out, a friend of mine with an identical car/tire was on his third set of tires.

Read the TireRack articles. You’ll find when they refer to the recommend pressure for a tire, they are NOT referring to the door placard.

paulv

That's why I posted that link to the TireRack articles.

Regards,
Paul...

ATS

The tire pressures inside the door are not the same between cars.

The sticker on the E55 has different pressures compared to sticker on my E500. I know as I have checked at the dealership as I have E55 rims on my E500. (I am in Canada but the sticker is applied in Germany). Also I think the manual has diff pressures as well.

The E55 had higher pressure listed. The E55 car is also heavier by a couple hundred pounds I believe in the front.

I have mine at 33psi all around. When I go lower the car starts to dart the pinpoint feel is lost. I am running Z rated Conti's.

e1000

Overinflation may wear the center of the tread, but this discussion is about what proper inflation is. I think we all agree that proper inflation will yield the least amout of tire wear.

Generally, tires will provide more grip and traction with lower pressures. The reason is, with less pressure, the contact patch becomes larger, and rolling friction increases, therefore you end up with more traction, more wear (and also more heat).

Proper, and even overinflation will most DEFINITELY give better wet weather results. There was a test done by TireRack some time ago that proved this without a doubt.

I also have a problem following the plackard provided by the car manufacturer. While they do make the car, tires vary between manufacturers, wheel sizes, etc etc. I personally like to agree with MB Bob on this one.

Alan Smithee

OK, where do I start. Bob, your understanding of automobile tire pressures is entirely incorrect. Do what works for you, but (especially as a moderator) please don't preach incorrect information on a public forum that will jeopordize the safety of the unknowing.

He is a car salesman, not a tire expert, and he is wrong.



1) As was pointed out by somebody else, a tire may have applications on a variety of different vehicles. The sidwall maximum pressure is the maximum pressure to safely use the tire, period.

2) Is there a margin above the maximum pressure in which the tire can safely operate? Perhaps. But you don't know what that is, and that limit should not be tested OR PEOPLE COULD BE KILLED. This is serious.

1) No. As mentioned by myself and others, the recommended pressures are the best compromise of wear, comfort, and performance. If one has an understanding of the wear/performance concept, the pressures can be adjusted a few PSI in either direction. However, going 10-15 PSI higher as you are suggesting will result in unpredictable handling at the very least.

2) Believe your conspiracy theory if you'd like, but don't try to sell it to others.

1) Not correct. Lower profile tires on a given vehicle does not necessarily mean higher tire pressures. As mentioned previously, maxium pressure on the sidewall is not related to safe pressure for a given vehicle.

2) Not correct. Underinflating actually increases the contact patch.

3) Not correct. You have it backwards; the "one-size (pressure)-fits-all DOGMA" would be to assume the sidewall pressure of a given tire applies to both a 3,000lb Toyota with a maximum GVWR of 4,000 and top speed of 120mph and a 4,000 Mercedes with a GVWR of 5,500 and a top speed of 155mph.

Indeed, read the TireRack articles. The first sentence in the "How To Set Tire Pressures" article:

"Set according to the vehicle manufacturer's cold tire pressure(s) recommended on the vehicle's tire placard or in its owner's manual."

http://www.tirerack.com/tires/tirete...&currentpage=1

C43AMG

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MB-BOB

I don't know why my job as a moderator here precludes me from the privilege of having an opinion like any other member. Please read my signature below. My opinion is just as valid as yours, so deal with it.
I suppose I should have prefaced my remark by saying that my car "salesman" was a well regarded amateur racing personality in the St. Louis area. He knows more about high performance cars (from experience) than just about anyone on these forums.
Please quote me where I said to run your tires at maximum sidewall pressure, or above. I set my tires at 5%-10% under the max, which allows plenty of safety margin, considering I drive my car to commute to work daily, which means it is barely loaded at all.

As I have said before, my car rides and handles as well or better than it does with the tires set to land barge wallow mode. The car reacts quicker to steering input, the tires don't roll over on their sidewalls as much, and they don't squeal while plowing through a turn as before, because it does not understeer as much.

In wet weather, these tires grip so well that I can't make the ESP light come on. My tires are evenly worn across every groove, to the same extent on every tire, such that I have skipped a scheduled tire rotation, since the fronts are no more worn than the rears.

I would suggest that if you don't believe it, that you try inflating your tires to 10% under the maximum tire pressure and try it for a week. Can't hurt a thing. But of course, you feel my "status" here prevents me from making such a suggestion.

So, rather than argue with you, (which I am not) I'll simply be on my way, stating that there is no absolute rule regarding tire inflation in a constantly changing technological world. It makes no sense to ridicule me for my views, or thinking outside the box, which obviously work quite well for me, thanks.

Alan Smithee

You are, of course, entitled to your opinion. However, you have represented your opinion as a fact.

See below (my use of bold type for emphasis). Conveniently, this is also one of the instances where you represented your misguided opinion as fact.

Barry45RPM

Bear in mind also, that the tire placard on the gas filler door is for any tire that MB has already spec'd out as an OE tire. The only reasons there may be a couple of brands on a car model are..

1. The tire manufacturer is unable to supply the number of tires needed to meet production levels at that time.

2. The MB engineers have determined that the alternate brand of tire shipped on your car is "just about as close as can be to their # 1 tire choice (known only to them, but can be guessed if one knew the percentage of the 3 tire manufacturer's tires on the entire model run. For instance, if Michelin was on the highest number of cars shipped, then the Michellin tire was their 1st choice for the vehicles design.

The tire placard on the door only covers the 3 or so tires that MB will put on the car at the factory. Not ANY tire you can buy & put on.

The MB engineers are trying to give you the perfect balance of ride quality, all weather traction & tread life. If you put that tie on a lighter or heavier car than the E, a different pressure will yield that "perfect balance", as long as it falls under the max inflation pressure on the tire.

No one "on the street" has as much education and information about the tire as the people who designed it, and no one has as much info on the car as the engineer in the design offices. It doesn't matter how proficient he is at using it, he wouldn't know where to begin designing one.

MB-BOB

Speaking of taking convenient liberties... not five sentences earlier in the same post you quoted, I wrote (note my emphasis), "My replacement Dunlop SP Sport A2s (44psi sidewall rated) are kept at 40-42psi, and after 20K miles they are evenly worn across the tread, and front to rear too." If you intend to quote my posts, keep them in context.

My meaning was perfectly clear. I am guided more by what the tire sidewall suggests than what the door pillar suggests. I stand by my remarks. To each his own. Thanks again.

MB-BOB

I believe the real reason MB has several tire suppliers is that MB doesn't want all their eggs in one basket. A work stoppage, or problem with a tire affecting one tire subcontractor does not affect MB production if there are multiple suppliers on hand to fill the gap. (Think Ford/Firestone SUV tire debacle.)

This is also an excellent way to leverage one supplier against the other for pricing. This is a common strategy/policy used by many large companies to control the provisioning of critical components from outside suppliers. I've worked for several such companies and have seen this strategy used countless times (from both the perspective of the buyer, and the supplier).

IMO, tires to a car manufacturer are simply commodity items, for which "just in time" delivery continuity and the cheapest price is just as important (if not moreso) as the quality of the product, loyalty to any given vendor, or adherence to a given technical spec. See below...

I did a search on the W203 forum on this topic, because it specifically was discussed in 2001 or 2002. Members were trying to figure out the random nature of tire brands on their W203s. But I could not find the pertinent thread. It apparently was lost in one of the many database glitches in the early days of the forums.

In 2001, the luck of the draw tires for the C-Class cars were Continental Touring Contacts (32psi), Goodyear Eagle RS-As (40-44psi, can't remember exactly) and the Pirelli P6s (51psi) that came on my car. I'm not sure this supports your theory about tires within a range that are approved for use with a placard that reads 29 front / 32 rear (same as the heavier E-Class, BTW). More supportive of the "tire is a tire is a tire" macroeconomic theory, in my view. But, as we have seen already, opinions vary.

csumt76

FYI, E55 placard states 35/35 for the standard pressure setting. Always run what the manufacturer recommends. Disregard what the tire says... or anybody else.

Flash Gordon

I have been inflating my tires about 3-4 pounds above the mfg sticker on the door for many years. I am quite happy with the ride and wear. I feel to inflate any car with over 40+ pounds will give a rather harsh ride and may blow out a tire when hit a nasty pot hole.

ClayJ

I have ALOT of cars - and ALOT of different tires on them; and I've been doing this for a loooooong time....

Tire sidewall; and evaluate wear, handling, braking, and ride - per car, per tire. And as use changes, so do most-desired tire fitment, and their respective most-desirable pressures.

THAT is how you do it.

edspider

Whew! When I posted this thread I wasn't expecting all this. My sticker says 28/33. After all this posting I feel like the dealer set 33/33 is probably just fine and so is 28/33. I think what I'll do is just drop to 30/33 as a comfortable compromise.

Thanks all (except the 10% below max rated rule. Now that one is way out there and I'm sure readers realize it.)

LAZARU5

The tire pressure sticker on my 2005 E500 4MATIC reads 29/34. After the first tire rotation I noticed that the rear tires were wearing faster in the middle. I ran with 32/32 after that until about 30000 miles. More recently I have been running at 31/33. Raising the front tire pressure definitely helped mpg. My overall average is 22.5 mpg and the window sticker rates the car at 16 city, 20 hwy. I replaced the tires this week at 44000 miles. They could have gone further but two tires were cupped and the noise was driving me crazy.