I've been driving a pretty long while, and over the years I've heard tips from autocross guys, tire guys, MB techs, and anybody in between, and there's always a different theory.

I've had some say you should run more weight up front, since the motor is heavier, and you need to support the weight. I've had some say you need less up front, so you have proper understeer for predictable handling. I've had some say lower in the rear unless you want excess oversteer, or are on a track. I've had some say run 35 all around for proper tire wear.

OK! So what's the real answer?

Say a certain car has a recommendation of 28 front and 33 rear, and then at speeds over 100, an extra 4lbs. My C300.

Are these recommendations based on the actual weight of that car, in light of the max pressure allowed for the tire? Is it because that chassis is tuned to work with with pressures in this gradient (chassis-specific handling characteristics)? Is it to preserve the tires? Or is it just for comfort on the "bell curve," sort of like 39k trans changes (aka if you're leasing, you never have to do a trans flush, even though it would be better to do it at 30)

Is it just the whim of the manufacturer and whoever is in charge or putting the sticker on the cap that year? :-o

I'm just so confused. On my C300 with 17s, I've found 33 front and 38 rear feels pretty good, from an everyday handling standpoint, though I havent had the car at its limits. Anything more up front makes the car's steering excessively susceptible to crowns in the road, although 35 all around feels really good in a straight line as far as ride quality.

On my 129 SL with 17s, and on other, older cars I've had 17s on, I felt like I had to run a minimum of 35 else the ride and handling felt mushy. I am now running 37r and 34f on the SL, and it seems to be a good balance.

So, does recommended pressure come down to:

1) Suspension/steering settings for that chassis
2) Tire life
3) Ride comfort
4) Just your own seat of the pants preference, and anything as long as it's not 10 or 50 psi will do just fine?

__________________
former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL

Obviously,You're gonna Inflate to whatever YOU THINK is proper.
(Based on the Gauge more commonly known as the "Nether Regions" below your belt.)

Those Silly AR Engineers in Stuttgart could have saved themselves ALL that
Work (Empirical PSI Testing for EACH Chassis.)
"Vhy zhould ve bother? Will will not follow our Directions about inflation Anyway!"


You can bet the Farm they're order of priority was/is:
1.Safety
2.Handling
3.Comfort

I've got a better question/survey for you:

Do the Maintenance people working for the Major Airlines set Tire Pressure by the Ass-O-Meter method ?
AND
What Criteria do the U.S.Marines use for setting tire pressure on their Planes?
(I sincerely believe the answers to those two questions will tell you how to go about setting the PSI on your Mercedes.)

Only People I know of who screw around with inflation pressures on things that fly are Bush Pilots...
Out of Necessity.

As Always,Your Mercedes,Your Pleasure.

Except,you're driving the thing on the Roads with the rest of us.

Do P.I. attorneys check inflation pressures (or evidence of )after an Injurious Wreck?

__________________
'84 300SD sold
124.128

What does it matter? Oh I dunno, finding the optimal balance of handling and safety? The people who went by the FSS maint schedule a few years back THE WAY THE ENGINEERS supposedly intended, ended up with sludge and trans problems. I guess by your logic, people who advocate varying from MB recommendations are morons? SURELY you don't mean that.

Jesus christ, it was valid question that I've heard many answers to. I'm only trying to understand the "why's" "how's" and other possibilities based on a myriad of other seemingly-credible advice.

__________________
former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL

And Ask:

1-866-866-6605
8 a.m. to 8 p.m. (M-F)
8:30 a.m. to 4:30 p.m. (Sat.)
(Eastern Time)

Ask to Speak to a Tire Engineer.

(AND I seriously doubt you will ever be able to find an Engineer who worked for
Mercedes at the time who'll take any responsibility for the FSS foolishness.
[That Debacle was ALL Marketing] )

AND as for your sophomoric attempt to some how Imply that I have said or thought anything Derogatory About BW...
That's just outright Cat Poo (Spell the last two words, SLANDER) !

Over or Under Inflated tires are Deadly,AND there are Many who visit here,who are not aware of the Dangers.

__________________
'84 300SD sold
124.128

I'd like to know so post results.For instance tire pressures have changed my new set has 44psi max.Anything below 40 looks flat.

__________________
1999 w140, quit voting to old, and to old to fight, a god damned veteran

Yeah! So I guess both myself and Oldsinner are both so stupid that we have to ask asinine questions right?

Oldsinner, we'll hopefully get some relevant, productive replies at some point.

__________________
former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL

Will,

I guess tire pressure can bring up deeply held opinions sort of like an oil thread.

With a couple of million miles maintaining cars behind me and about half of that in MB's, along with serious tire interest (I even have my own rim clamp tire machine and computer balancer because I can't get the tire stores to mount and balance to suit me) I do have some real world tire experience and knowledge.

I have learned that the tire pressures published by MB usually work out well for MY type of driving. Over the years I have learned to add a couple of PSI on the back tires, particulary the right rear, to aid tire wear.

It is also important to check and adjust pressure when the tire is cold, preferably in the morning, but with at LEAST a one hour cool down period. In the Winter I add a few pounds all around to make sure an extra cold day doesn't result in low pressure.

Even a couple of pounds too low can cause excessive center tread wear.

Hope this helps.

__________________
2001 SLK 320 six speed manual
2014 Porsche Cayenne six speed manual

Annoy a Liberal, Read the Constitution

I run about 38lbs front and rear in my SD.

It's an attempt to gain maximum MPG and feel for the road.

Never knew I was endangering the population...

__________________
On some nights I still believe that a car with the fuel gauge on empty can run about fifty more miles if you have the right music very loud on the radio. - HST

1983 300SD - 305000
1984 Toyota Landcruiser - 190000
1994 GMC Jimmy - 203000

https://media.giphy.com/media/X3nnss8PAj5aU/giphy.gif

This is good info, especially from Larry. Never thought about inflating one side vs the other for wear, however I'm more looking for best balance of firm ride and good handling, while still being safe for emergency maneuvers, not jarring my spine, and not doing anything to cause EXCESS wear.

__________________
former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL

The answer is difficult to give without the proper variables added...road conditions, average ambient temperature, original tires, OEM rims, etc...the list goes on and on.

My F250 has a decal that says 45 psi...but the tires are not stock, and the manufacturer of the tire, as well as my driving conditions, require 80psi in the rear and 65psi in the front. These pressures are adjusted for my needs, as it is used off road as well as on hard surfaces.

My Tahoe also has different tires than stock...I've had to adjust the pressures over the last 2 months to be able to get proper tire wear.

My SL doesn't have what it came from the factory with either...i put new tires on from a different manufacturer and had to adjust the pressures on all 4 of them for even wear as well as handling and stability.

Each case is different. However...if you have the tires the vehicle came with, or exact replacements (same belts, same ply and same tread) then I would stick with pressures within +/- 5% of what the automobile manufacturer recommends.

Just my opinion as an engineer and wheeler.

__________________
1987 560SL
85,000 miles

To compress ignite's point, what's the guidance when you change tire and/or wheel size? My 87 300D runs 205/55-16s in place of 195/65-15s. No US spec 124 came with this tire size. Is the vehicle manufacturer pressure guidance still valid?

A bit of a tangent but with the same objective -

In the high performance arena I notice they measure temperature across the tread after a hard run. This seems more to analyze corner loading and wheel alignment. For mortals, can optimal tire pressure be determined by analyzing tread temperature? Maybe find the lowest temperature between vehicle manufacturer recommendation and tire manufacturer maximum. That should bracket it since I never see recommendations for pressures lower than vehicle manufacturer recommendation nor tire manufacturer minimum pressure ratings.

Sixto
87 300D

The W124 came with 195/65/15 [a P.O. fitted 205/65/15]
I've fitted Michelin Primacy MXV4 205/65/15

Michelin says to follow the Mercedes Tire Inflation Placard on the Fuel Fill Door.
[Unless you're Crazy enough to run over 100MPH,Then add 3-4 PSI to each Tire.]


Mercedes says:
"Sie haben einem Unpassenden gepasst, das nach dem Größereifen zu Ihrem Mercedes angeordnet worden ist, Schande auf Ihnen!
Wir haben keine Informationen.
(Unsere Rechtsanwälte haben uns sagen dies gemacht)."


YMMV

Your Mercedes, Your Pleasure.

__________________
'84 300SD sold
124.128

And thus we have the wheel and tire forum

Sixto
87 300D

This is the kind of stuff I'm looking for. Obviously, on a car made in 92, when I'm plus-sizing to 21st century tires, with all suspension parts sorted out and not worn, there have to be some variances. Even on an 08 car, 28psi seems grossly low for 17s, and it's hard to think of 35psi as some whacko number. I know guys who run 40, TDI guys especially, which I think is excessive. However on a 4200lb 500SL, with a tire max pressure of 50, I'd think I could run more PSI than that same tire on a 3500lb car - no? The higher the GVWR, the higher the PSI needed. Correct?

__________________
former: 83 300D, 97 C230, 93 400E

current: 08 C300 Luxury , 92 500SL

In racing, they like to try to get the temperatures at the outside, middle, and inside of the tread as close to the same as possible. I'm not sure how well this would work in "normal" driving. I have an IR thermometer so one of these days if I get bored I may start checking tread temperatures.

I'm currently running 38 all around in my 300D. I was running a bit less before and the increase seems to have helped the handling. I'm guessing the tire was rolling under too much during hard corners before.

__________________
Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.