jhpmbusa

What PSI do you put in your 18inch Sports Package tires? I put 40. any suggestions?

cetialpha5

Tire pressures are usually posted on the door jamb or on the gas cap. I'd go with those numbers.

fogozito

32 front
35 rear
E400

thefisch

+1. Need to know what MB recommends for our car as optioned so best to check these places. Door placard will give the pressures for max load whereas gas cap may give pressures for normal and max loads.

Arrie

37 psi front
38 psi rear

I have 245/40-R18 all around but the car is Avant Garde without 4-Matic.

bellavance

ua549

There are 3 sets of tire pressure values shown on my car with 245/45x18 Pirelli tires. Normal load (32/32), maximum load (33/39) and high speed adjustment (+4) numbers are on the fuel filler flap. Extra load values (37/43 are on the door jamb which correspond to the maximum load plus high speed adjustment. I use the normal load setting of 32 psi all around.

YasS

Do you guys know which time is best to fill up your tires with air? You can see that the tires are low first thing in the morning. Then the psi gradually increases when the tires get warm as you drive .
So when should I adjust the psi to the sticker on the door jam.
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ua549

Tire pressures should be adjusted before driving when the tires are cold.

cetialpha5

Those are cold inflation pressures. I believe they can increase by as much as 4 psi while driving. So you can adjust the extra psi.

NFAREVIEW

I would get them purged and filled with nitrogen. It keeps you from constantly having to check and they won't fluctuate a ton like air will. My Ducati came with nitrogen fill and it's all they do. Of course your pressure is uber important when your contact patch is 2x2" lmao.

dudley07726

guhvies

^^The different pressures are for different loads and speed.

cetialpha5

Air is already 80% nitrogen so going to 95% is a little over rated. It's probably fine if the tire shop already does it, but I wouldn't go out of my way to get that done and pay for it for an everyday driver. Motorcycles and going to the track would be different story.

https://www.tirerack.com/tires/tiret...jsp?techid=191

saintvir

ua549
I picked up my car yesterday. I have same values in those two places. Dealer told me to follow 37/43 as posted on the door jamb.
TPMS says all four tires are at 39 psi. Go figure. (I have Goodyear Eagle Sports 245/40R19 mounted).

Would 32/32 be too low for my tires?

ua549

I use 32/32 on my car with light to normal loads in city driving. Be advised that higher pressures are needed for heavier loads (4 passengers) or higher speed driving.

jhpmbusa

Also its 32 cold psi. once you drive around for a bit it will go up 3 to 4 psi. But to be honest should the 32 psi rule apply to both 18 and 19s?

idrive

Normally the taller the tire the higher the air press. A 295/55/18 would run a higher pressure than a 295/40/18. The circumference doesn't matter nearly as much as the height and then the width.

Best place to get your recommended air pressure is next to the gas cap.

Cambridgehank

cetialpha5

Just depends what line of trim you have. According to the brochure, you could have 17, 18 or 19 inch rims.

http://www.auto-brochures.com/makes/...Class_2018.pdf

caseybalbachan

If i can go a little off topic here, what if you changed tire and wheel size from what the car originally came with, then what is the recommend tire pressure to use? Would this be the same as what recommend in the door jam?? I always see people asking for the proper tire pressures and everyone resorts to the "check door jam." But what do you do if you changed the sizes of both the tire and wheel?

Cambridgehank

I get the rim size. But what is the difference in a 40 versus 45 number?

cetialpha5

The 40 and the 45 are aspect ratios. Basically when you go up an inch, you decrease it by 5 or if you increase by an inch you decrease by 5. Usually that rule of thumb is only good for one step up or down. You can actually do your own calculation. Basically the 245 is the width of the tire in mm. The 45 is the percentage of the height of the tire based on the width. It's basically to maintain the same ride height with a 18 or 19 inch wheel.

midwestamv8

E43 w/ 20" pirelli run flats. I run the recommended 40f/38r. Rides nicer than the 46/45 the dealer had me at on delivery.

NOMRW8NG

The proper way to determine pressure with an alternate tire size is to look at load capacity. I found this Determining Air Pressure (Load Index Table) document that explains how to figure it out.

For my E, the stock tire is 225/55-17 97Y and the placard on the fuel filler door lists a cold inflation pressure of 32 psi front and rear for normal load. Looking at the table, I find that the load carrying capacity per tire at 32 psi is 1592 lbs.

The winter wheels and tires I purchased are 245/45R-18 100V XL. Looking at the section for XL, scanning across the row for load index 100 XL I see that I need 37 psi to have a load capacity of 1590 lbs per tire, just a little bit less than stock.