Captain Obvious

It sounds strange to me to run the rear tires significantly higher than the front. It isn't like there is any extra weight to support in the rear. It appears the front seats are nearly centered in the car, so the balance is going to be near perfect unless there are rear passengers. There will still be far more load on the front tires when braking.

Is the rear suspension soft, are they trying to ensure some level of understeer, is it rear passenger/cargo accomodation?

If the concensus is that it is to induce understeer, I'll probably run my rear pressure within 2 psi of the fronts.

Any comments?

jyg e500 maybe

bmw fives have 4 lbs diff,. 4 lbs higher in rear,

DavidNJ

Its a balance, not a load thing (except when you are comparing full load capacity). Higher pressure reduces the slip angle in the rear making the car understeer. And gives them the higher capacity to deliver power and cornering concurrently.

DWP

The 1/03 Road & Track test of the E500 says that the E500 has a 54/46 front/rear weight distribution, with driver. The E320 presumably is a bit closer to even, although I don't know that for a fact. With 54% of the weight on the front tires, the W211 wouldn't seem to need much help from unequal tire pressures to ensure understeer. I have to wonder if it's a liability thing with M-B as much as a balance thing. In other words, is M-B recommending higher tire pressures in the rear to ensure that even the blivet who turns off stability control to play boy racer won't have his car swap ends and park against a tree?

DavidNJ

Its a shock, spring, bar, and geometry thing. On my race car, before going to a soft spring setup, I went from a LF325,RF350,LR200,RR200 with a 1.25" front bar to a LF275, RF300, LR225, RR240 with a 1" front bar. All to get rid of understeer. Also changed to a longer RF upper control arm (lowered roll center), adjusted front camber, and changed rear trailing arm angle (to cure a power oversteer problem). All with tire pressures like LF14, RF 26, LF 16, RR 26. 48% rear weight by rules.

To balance the slight front bias, they place more load on the outside rear (higher rear stiffness). That higher load requires more pressure.

JPM

The tyre pressure sticker on my E320 CDi only calls for higher rear pressure if carrying rear passengers and a lot of luggage, otherwise front and rear are equal.

Barry45RPM

So its an MB-USA specified special sticker printing thing then, although it lists 2 different inflation rates... 1 set for speeds under 100 MPH & 1 set for speeds over 100 MPH.
...Maybe there's 2 sets of inflation pressures just to impress us, cuz it aint easy to go over 100 around here!!

Captain Obvious

I wonder if that is a change for '05, or just the CDI. The CDI is 160lbs heavier up front than the gas model.

RJC

Do the pressures just vary with staggered tires set up's or not?

JPM

Not according to MB, same pressures apply for all tyre options. However, Brabus (for one) disagrees, specifying higher rear pressures (something like 35F, 40R) for their staggered setups - though this may be in combination with a Brabus suspension package. As already mentioned earlier in this thread the car's suspension setup will have a strong influence on the effect of any front/rear pressure differential.

ATS

In my door it states to have higher pressures for speeds over 100 and I have W rated tires with the Appearance Package.. Look inside your door. It may be only for W or Z rated tires..