mbates50

Door label states 40psi in back
Gas tank door states 35psi,(normal), and 40psi, (max), in back

Front's are about the same

So which is it ?

Thanks

gkgeiger

Always the gas door. I had to call MB to verify. For the life of me I don't understand the two different recommendations

jadatis

Tirepressure advice is to give the tire a deflection that dont give to much heatproduction at the speed its given for.

this deflection is made by the combination of pressure and the load on the tire.

Your 40 psi is for fully loaded or probably even for overloaded.
Your 35 psi is for the loads on tires when normally loaded.

So if you only drive with driver and a little load, the 35 is more then enaugh, but for towing and overloading the 40 psi is needed.

Because the loading of a car is mostly on rear , the rear advice is more different. The loads on front tires is more constant.
Mind that the weigh of front seaters ( driver and codriver) is already almost between front and rear axle so that weigh is devided <> 50/50 over the axles.
Rear seaters 3/4th on rear axle and 1/4th on front. And loading in trunc is totally on rear axle or even behind .

Also for higher speed the tires need higher pressure , tire-and car-makers have a system for that .

Before 2000 the pressure advice was calculated using the axle loads and maximum technical car speed , but also for up to 160km/99m/h sometimes in Europe. Even normal use advice was calculated for axleloads determined by the car maker for 3persons and a little load in car.

After 2000 , to my conclusion has much to do with the Ford/Firestone-Affaire, often pressure needed for maximum load of standard tires was given , wich is in American system for standard load tires 35 psi.
Can be that your tires are XL/extraload/reinforced for wich this pressure is 41 psi.

So I cant write wich system your carmaker has used, but as Pigheaded Dutch self-declared tirepressure-specialist , i am able to calculate pressure for you , if you can give me tirespecifications and accurately determined loads on axles for the situation , or better even seperate wheel-weights .

gkgeiger

Like I said, the gas door.

jadatis

Yes the 2 different advices on gas door are more specific for the use.
That on door label is only so the car maker cant be held responcible if lower pressure is used, but if they where wise, they had removed that in the gas door, now you still can hold them responcible for advicing to low pressure.
Only for their andvantage , becouse for the costumer ( we) the more different specific advices are better.

Yudging by the values in gas door , I assume the pressures are calculated .
The 40 psi is not a standard AT-pressure for any tire so must have been determined by some kind of calculation.
And then its a coincidence that the 35 psi is such a standard AT- pressure.
I call it AT-pressure because on LT tires this pressure needed for the maximum load up to max speed of tire ( or if lower 160km/99m/h) is only given like this mostly, "maximum load xxxx lbs AT yyy psi ( cold)"
On SL and XL// tires only maximum allowed cold pressure is given and AT-pressure is lower ( that 35 and 41 psi in american system).

But mostly on that pressure plate in the door , also the GAWR's ( Gross Axle weigh Ratings) are given , wich car-and tire-makers use to calculate the pressure for. Try to find them and give them here , together with the tire specifications ( maxload , tirekind to determine AT-pr, and speed code), and I will calculate and see what they did.
Can be that lower pressure is also save for the tires , wich gives more comfort and gripp.

mbates50

Thanks. I've decided on 35/front and 38/back.

branmin

33's from cold front and back for a softer and more comfortable ride if you don't push the car

mercnewbie2

Wrong forum, deleted post, sorry

Sky1

Same here, have had 33 all around, or up to 35 w/o any issues and done so since I got the car.

Agree it’s a much smoother ride. High pressure results in a firmer harsh ride.

rmorin49

I'm still a newbie. For those with long term ownership have you found even tire wear running 33 psi F and R using extended mobility, i. e, runflats? I do add 2-3 psi in the rear with luggage in the trunk on road trips. Thanks.

rorywquin

Are you looking at the correct setting. Mine has 18" &19", loaded and not loaded settings!

TennesseeZ4

I have found with my 19" staggered set up that 35 psi front and 38 psi rear gives me a great combo of comfort and handling with the Michelin Pilot +3; if I plan to do a longer drive with a lot of interstate, I bump that by 1 psi on both ends. I am running nitrogen in my tires and over the years have found that to be the most stable gas in that environment.

rmorin49

Tennessee, these are the non runflat version? All season +3?

TennesseeZ4

Affirmative, non-RFT, and the all season. I have about 10K miles on them now and the wear pattern is consistent across the tread area.

Sky1

I also have the AS 3+ and find these tires very noisy. I’m comparing to Pilot Sport 4s on a BMW.
Am thinking of changing tires to Pilot Super Sport, or Pilot Sport 4s.

Do you or other members find the AS3+ noisy, humming, or low buzzing/vibration sound?

bob55

Yes, the Ultra High Performance A/S 3's do seem somewhat 'noisier' than many of the max performance summer tires, (such as the excellent Pilot Super Sport Tires), but the Pilot A/S 3's also provide a more 'cushioned' ride because they have a softer and more flexible sidewall than any of the max performance summer tires.

My 2013 SL 550 just happened to have what were apparently 'new' 18-inch Michelin PIlot A/S 3 tires installed when I bought the car just over a year ago. Had that not been the case, I would have installed a brand new set of 18" Pilot Super Sports Tires that I had originally purchased for a SL 500 230 that I no longer own. Those Super Sports now serve as 'a backup set of tires' for my 2013 SL 550. Fortunately, (for me), 230's with the optional 18" 5-spoke AMG Wheels, required
the exact same tire sizes, (front and rear), as (2013-2016) 231's with the factory stock 18" Twin Spoke wheels.

Perhaps, "eventually', I'll finally need to mount that spare set of Pilot Super Sport Tires, but that won't happen until the A/S 3's, (which show very little wear at present), are in need of replacement, which BTW could take 'several years' since I am not putting that many miles on the car these days. (I have several other cars that I also drive).

That said, I don't have any intention of parting with my 231 anytime soon, so yes, at some point, I actually do expect to finally mount that 'spare set' of Michelin Pilot Super Sport tires on my SL550.

rmorin49

For those who may be thinking about UHP AS tires, check out the Continental DWS06s. I put them on my C7 Corvette and also on my wife's RX. They are great tires.

Dr. Manhattan

We're all running nitrogen in our tires...you're just running a bit less oxygen than the rest of us.