# AutoX Tire Pressure Q: E46 ZHP 18"



## SteveMD (Apr 22, 2002)

You E46 M3 pilots should be able to help. By how much should I bump my tire pressure up for autoX? 

The general rule for all cars seems to be by 10 psi. On my ZHP 330i, the max pressure front, fully loaded car is 39 psi. Should I add 10 psi to that?


----------



## Mr. The Edge (Dec 19, 2001)

49 sounds awfully high to me


----------



## SteveMD (Apr 22, 2002)

I agree. I don't have the car here at work so I can't go check the max. inflat. pressure on the sidewall. 

The door sticker says 32 psi front for light load (just me). As an experiment, I took it up to 35 psi for street and kinda like that. 

I left the rear alone at 38 psi (light load) as lower psi in rear supposedly helps reduce under steer.


----------



## Chris330Ci (Jan 23, 2002)

SteveMD said:


> *The door sticker says 32 psi front for light load (just me). As an experiment, I took it up to 35 psi for street and kinda like that.
> 
> I left the rear alone at 38 psi (light load) as lower psi in rear supposedly helps reduce under steer. *


True, but you will still have an understeer prone car if rear psi is higher than front psi.


----------



## SteveMD (Apr 22, 2002)

Chris330Ci said:


> *True, but you will still have an understeer prone car if rear psi is higher than front psi. *


Thanks for the chart.


----------



## Jetfire (Jun 20, 2002)

FWIW, my M3 seemed to work very well last season with the fronts at 41 psi and the rears at 38. I would typically drive around town with 35 psi all around. Raising the front pressure more than the rear helped to overcome some of the low-speed understeer.


----------



## FSelekler (Jan 15, 2002)

I am not sure what tires come with the ZHP, but I have the Michlin Pilot Sports with 225/40/18 and 255/35/18 sizes (if they match yours).

Last auto-x 41.5 front and 39.5 rears workout very well, I might just add 0.5 to rears next time as I had a tad of oversteer, which was fun actually  

10 psi over regular street on the fronts is OK IMO; but for the rears I would not put more than 3 psi as max.


----------



## FSelekler (Jan 15, 2002)

I just hate (nothing against you Chris, not personal at all) when the chassis dynamics are summarized in a table like that. Uninformed picks it up and thinks he got all he needs...

Sorry, I just could not help myself :thumbdwn:


----------



## alee (Dec 19, 2001)

Don't blame him... I believe that chart is from UUC.


----------



## FSelekler (Jan 15, 2002)

alee said:


> *Don't blame him... I believe that chart is from UUC. *


Not blaming him at all, I apologize if it comes that way Chris, really was not my intention. I am sorry.

FT!


----------



## Chris330Ci (Jan 23, 2002)

No big deal...and Al is right. I swiped that from UUC to prove a point to a friend once...


----------



## brave1heart (Jan 7, 2002)

I've never heard of a 10 psi rule. The best indicator are those little triangles at the end of the outside treads. If those are getting worn out, that means your tires tend to be underinflated for the weight of the car and the type of driving that you do. Ideally, the tires should have just enough pressure so that when the car is pushed hard in corners, the tire patch will expand for better grip but without actually getting past the triangles. Too much tire pressure is not good because the tire won't be able to adjust the patch in hard cornering. I run 32/34 F/R on the street and ~ 37/35 F/R on the track in my 325i, which weighs ~ 3,250 lbs.


----------



## SteveMD (Apr 22, 2002)

FlyingToaster said:


> *I am not sure what tires come with the ZHP, but I have the Michlin Pilot Sports with 225/40/18 and 255/35/18 sizes (if they match yours).
> 
> Last auto-x 41.5 front and 39.5 rears workout very well, I might just add 0.5 to rears next time as I had a tad of oversteer, which was fun actually
> 
> 10 psi over regular street on the fronts is OK IMO; but for the rears I would not put more than 3 psi as max. *


Yes, I have the same brand/sizes on the ZHP. Thanks for the discussion here.


----------



## TGray5 (Jan 22, 2002)

All of the above advice is similar to what I've found. Basically, high 30s worked well with my M3 and a few pounds less in the rear. Use some chalk or window paint on the sidewalls to see how much rollover you are getting. I would not run anything higher than 40 though.


----------



## SteveMD (Apr 22, 2002)

"Uninformed" found that 43 psi front (hot after last run) and 40 rear worked ok. The tiny triangles got eaten on the front tires. Can still see them on the rears but they have been nibbled.


----------



## Nick325xiT 5spd (Dec 24, 2001)

Idiot here pumped up his tire pressure after the second run after playing with Clyde's pyrometer.

Third run sucked, and so did the fourth.


----------



## ·clyde· (Dec 26, 2001)

Nick325xiT 5spd said:


> *Idiot here pumped up his tire pressure after the second run after playing with Clyde's pyrometer.
> 
> Third run sucked, and so did the fourth.  *


Anything to blame other than the driver


----------



## Nick325xiT 5spd (Dec 24, 2001)

[email protected] said:


> *Anything to blame other than the driver  *


Steering rack.:bigpimp:


----------



## ·clyde· (Dec 26, 2001)

Nick325xiT 5spd said:


> *Steering rack.:bigpimp: *


Anything else?


----------



## TeamM3 (Dec 24, 2002)

the triangle/corner rollover theory should only be applied to the front tires. Once you determine the proper front tire pressure you can set the rear tire pressure to whatever it takes to get the balance you are comfortable with.

BTW, that parameter chart listed above is general and does not always apply as shown for every vehicle, in some applications the opposite is true, it just depends ...

ps: when you have a chance could you please measure and post the swaybar diameters for your ZHP, there is some question about whether or not they increased over the other 330i packages. thanx,


----------

