tire pressure
 

I just put a new set of tires on the car. My question is my tires are rated to 42 psi but my car says to go 28 in front and 32 in the back. Which one should I go by? I want to get the most life from my tires and the best fuel mileage but I also want the car to ride and handle like it's supposed to...

Every vehicle I've owned does better with the vehicles ratings. They handle better and tire wear is very even. (I put 40-50K miles/year on work vehicles.)

The sidewall rating is for maximums for that tire, regardless of what vehicle you install it on. I know, there are many tire dealers that will tell you different but take note of the fact they want to sell you new tires.

I've found this is related to the tires you have installed. I have Nokian WR's 195x13's installed on my 300SD and I have found around 33psi to be the ideal front tire pressure. less than that and I find steering precision suffers.

the maximum pressure rated is for heavy loads or high speeds.
note on the gas door, there are adjustments to the posted tire pressures, for loads in the trunk, towing, and high speeds... (not that a 240 is capable of 100+mph... without tail winds/cliffs...)

I assume that your car was not originally equipped with P-metric tires and MB's inflation recommendation was based accordingly. I recently switched my P-metric tires on my Xterra to LT-tires, which are designed to operate under higher tire pressures. I contacted the tire manufacturer, told them what the original tire type and size was, what the new tire size and type is, and Nissan's air pressure recommendation as found on the driver's door.

They got back to me with recommended tire pressures, which I use. Apparently they look at the maximum weight that the original tire type is designed to support at the car manufacturer's recommended air pressure and determine what PSI the new tire has to be inflated to in order to support that same amount of weight.

Mess around with different pressures until you find what you like in terms of ride, handling, and fuel economy. I wouldn't go lower than 28/32, but I would try some higher pressures. If you want to get fancy you can also use an IR thermometer to measure the temperatures at the inside, middle, and outside of the tread and try to get them as close to even as possible. I used to run my 240D at about 36 psi all around.

Ok, thanks for the input. Right now I have them set at 28/32 and the car rides very nicely. I might go up to 30/34 to get the car to tighten up a little bit in corners. On my last tires I went to 40 all the way around and that was definitely too much! These new ones are 205/70/14 Khumo's, so far I'm very happy with them.

36 psi all around for me as well.

my tires are 195 70/r14 sized generals altimax rt.

The fronts are always at a lower psi than the back. So I usually run my tires up near the max but keep the difference between the front and rear. It's something like 6psi difference.

Low pressure will cause your mileage to suffer. If you run the pressure above what the door plate says you'll get better mileage, but the ride may not be as soft.

I run 32 all around. Makes no sence to have them at 28-29 it just feels better

When I was running the pressure on the 240D with 195-70-14 at 28 - 30lbs, my milage on the Hwy was 28-28.8mpg.

Then noticed the side wall mentioned, max pressure 44lbs. so raised it to 40-42lbs, and the milage shot up to 31+mpg.

This last trip to Oregon and back was. 32.83, 31.80 hwy in town mix, 34.10 and 33.42. this according to the GPS. we just got back home tues the 16th.

Charlie