northernmonkey

i think the actual reason for different pressures at the rear is a very complicated one involving that old school favourite of mine physics (pressure/volume/mass etc).


i remember a few yrs ago a motorsport guy i knew told me one reason was that if you ran at equal pressure all round, you would most likely encounter a lot of understeer in a rwd drive car. His "for idots" way of describing it to me without going into technical things was that raising the rear pressure will make the rear contact patch slightly smaller, thus decreasing overall grip. This means the car will have less understeer and will neither be faster or slower than with the equal
pressures.

I am sure there is also a lot more involved in making the calculation but that simple reason was all I cared to know about

530E60NL

So a higher pressure in the back makes the car oversteer more than understeer.. I like that more then understeer so I will keep the higher pressure for now.

northernmonkey

mine was a simplistic view of things....I'm sure bmw take a lof of other calculations into account, like differences between springs fr/rear, diffs between shocks, tyre widths etc etc, even maybe rotational speed differences between front/rear......

I think it is fairly common on car likes these (bmw,merc,audi,saab) etc to see higher pressures recommended for the rear tyres.

E60COYOTE

Great discussion! I now realize I am running the wrong pressures. I have 245/40R18s all around and was running 29/35 (front/rear). Obviously, I miss-read the chart. Now I realize I should run 32/38. (or 36 all around because I am usually the only one in the car)

ANy know what the lug torque should be?

northernmonkey

lug torque?

if you mean "how tight should the wheel nuts be" as we say where i come from originally LOL

i think most bmw's are 100-110nm

530E60NL

Anybody have such a wrench?? Since I am changing my winterwheels and summerwheels myself this could be handy I think. I used to do it by hand and feel.. So tight is tight but not too tight was my idea about it.

What does such an wrench cost??

northernmonkey

here's one on uk site...i'm sure they can be bought cheaper, just need to check the ony you buy has the right range (nm's) for what you want to use it for.

530E60NL

Thanks northernmonkey.. Checked out the torque wrenches over here and alread e-mailed a guy about one he is selling on internet!

530E60NL

Talking about tirepressure.. I want to buy a tirepressuregauge.. I've found a digital one that is only 19 euros! My only concern is the accuracy. I don't want to buy a gauge that isn't accurate because I can go to the gasstation to get innacurate pressures on my tires.


edit: Found this one at the halfords site for 13.95 euros. What do you think???

my530i

I think you should buy three different brands of tyre pressure gauge to check for accuracy. You'll have +/- 3psi skew in most typre pressure gauges.