# zhp tire pressures, reduce understeer, neutral ride



## allaboutme (Dec 22, 2003)

any agreement on a good tirepressure for the entire car all around? i've heard that having the same all around will reduce the understeer but that may be conjecture... any solid evidence?

what's everyone else running?

for reference, manual says 32/38 for full load (4 persons) and 39/46 for max load (5 persons+luggage)


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## Rich_Jenkins (Jul 12, 2003)

I use the recommended pressures plus 2 psi.


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## GregD (Feb 5, 2003)

I tried a variety of pressures in my tires and settled on 34F/38R. I find the handling to be pretty neutral with just a little understeer in most situations.


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## Nick325xiT 5spd (Dec 24, 2001)

My M3 is currently running 41/39.


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## philippek (Jul 31, 2003)

38/40

Got that recommendation at my first autox, and I find that it works fine for me all the time.


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## Dr. Phil (Dec 19, 2001)

Currently using 36 all around at recommendation on tech when we mounted M3 size tires. OEM sizes I ran 36/38 which gave me just enough understeer to live with


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## BloodRedHog (Mar 9, 2004)

Would it matter which brand tire you were running?


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## Rich_Jenkins (Jul 12, 2003)

BloodRedHog said:


> Would it matter which brand tire you were running?


Providing of course you used BMW synthetic ZHP air, no, I would not think so.


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## BloodRedHog (Mar 9, 2004)

wingspan said:


> Providing of course you used BMW synthetic ZHP air, no, I would not think so.


My dealer sells that for $4.99/gal. BTW. :rofl:


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## PhilH (Jun 7, 2002)

I'm currently running 38/38 on my 18s.

I find the front end too nervous on the highway with the fronts anywhere over 40.


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## mkh (Mar 24, 2003)

BloodRedHog said:


> Would it matter which brand tire you were running?


Yes it does. The Toyo T1-S is very sensitive to tire pressure. In the beginning, I was using 38 all around and I don't like it. The ride suffers significantly, and the steering feels too light and disconnected on high speed. Yes, it does reduce understeer quite a bit compared to the RE040 at the same pressure. Now I lowered it down to 36 all around, and it feels much better, with just a little understeer. Since the tires are new, I'm still experimenting. But I think I can live with this setting for a while.


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## MysticBlue (Jun 20, 2003)

38/40

Like Phil, I noticed a lot of rut tracking and twitchiness with the steering if I had the fronts over 38. Strong Strut front tower strut took care of that. Made a huge difference.


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## GregD (Feb 5, 2003)

MysticBlue said:


> 38/40
> 
> Like Phil, I noticed a lot of rut tracking and twitchiness with the steering if I had the fronts over 38. Strong Strut front tower strut took care of that. Made a huge difference.


 :wow: 38/40 is what I used on the track. Do you find the centers of your tires wearing out before the edges? Also, I found that high of air pressure to fairly detrimental to the ride for a rather small handling advantage. I ran 38/40 at the track primarily to prevent the tires from rolling over onto the sidewalls too far. :dunno:


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## Moderato (Nov 24, 2003)

I have the 330I SP with the 68M wheels (225/45/17x7.5 F & 245/40/17x8.5 R). I've been using 36F/38R which has worked good for me. I'm still trying to figure out why BMW recommends 32F/38R on a car with 50/50 weight distribution. I know those pressures are supposed to reduce oversteer, but is that really necessary when you have a staggered setup with DSC? What about tire wear? The fronts have to be under inflated at 32, either that or the rears are over inflated at 38. Would 36R be too low for my 245/40's? I don't want to risk bending the rim. I still think that equal pressures all around would make sense with equal weight all around. Maybe it has something to do with the staggered setup and lower profile tires in the rear? :dunno:


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## allaboutme (Dec 22, 2003)

Moderato said:


> I have the 330I SP with the 68M wheels (225/45/17x7.5 F & 245/40/17x8.5 R). I've been using 36F/38R which has worked good for me. I'm still trying to figure out why BMW recommends 32F/38R on a car with 50/50 weight distribution. I know those pressures are supposed to reduce oversteer, but is that really necessary when you have a staggered setup with DSC? What about tire wear? The fronts have to be under inflated at 32, either that or the rears are over inflated at 38. Would 36R be too low for my 245/40's? I don't want to risk bending the rim. I still think that equal pressures all around would make sense with equal weight all around. Maybe it has something to do with the staggered setup and lower profile tires in the rear? :dunno:


the 50/50 weight distribution question crossed my mind also... makes me think an all around pressure would be beneficial to the car.. what it "should" feel like..

if thats true.. i dont know which pressure to use.. maybe 36/36 ??


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## swchang (Oct 5, 2003)

allaboutme said:


> the 50/50 weight distribution question crossed my mind also... makes me think an all around pressure would be beneficial to the car.. what it "should" feel like..
> 
> if thats true.. i dont know which pressure to use.. maybe 36/36 ??


I've been running 38/40, but maybe I'll try out 36/36. The ride IS a little harsh with my current setup, but I attributed that more to Baltimore's potholes...


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## MysticBlue (Jun 20, 2003)

GregD said:


> :wow: 38/40 is what I used on the track. Do you find the centers of your tires wearing out before the edges? Also, I found that high of air pressure to fairly detrimental to the ride for a rather small handling advantage. I ran 38/40 at the track primarily to prevent the tires from rolling over onto the sidewalls too far. :dunno:


8000 miles and haven't noticed any uneven wear yet.
I didn't consider it to be that extreme...it's less than the max load recomendation, but I'll keep my eyes open for uneven wear.


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## GregD (Feb 5, 2003)

Moderato said:


> I have the 330I SP with the 68M wheels (225/45/17x7.5 F & 245/40/17x8.5 R). I've been using 36F/38R which has worked good for me. I'm still trying to figure out why BMW recommends 32F/38R on a car with 50/50 weight distribution. I know those pressures are supposed to reduce oversteer, but is that really necessary when you have a staggered setup with DSC? What about tire wear? The fronts have to be under inflated at 32, either that or the rears are over inflated at 38. Would 36R be too low for my 245/40's? I don't want to risk bending the rim. I still think that equal pressures all around would make sense with equal weight all around. Maybe it has something to do with the staggered setup and lower profile tires in the rear? :dunno:


Suspension design and alignment settings can make a huge difference to the understeer/oversteer balance of a car. The 3 series with a strut front and multi-link rear could be engineered to have almost any handling balance the engineers want.

I know the manufactures want understeer to make it safer for the average driver, but I think BMW does this less than most manufacturers, and at least on the track, I found equal pressures to give a little oversteer.


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## Moderato (Nov 24, 2003)

swchang said:


> I've been running 38/40, but maybe I'll try out 36/36. The ride IS a little harsh with my current setup, but I attributed that more to Baltimore's potholes...


Why not 36/38 ? 36R is actually lower then the minimum recommended pressure, and that would be a first for me, since I usually go over the manufacturers recommended pressure by 2 - 3 psi.


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## allaboutme (Dec 22, 2003)

Moderato said:


> Why not 36/38 ? 36R is actually lower then the minimum recommended pressure, and that would be a first for me, since I usually go over the manufacturers recommended pressure by 2 - 3 psi.


i don't know the physics... but with a 50/50 weight dist, why wouldnt all four tires have the same pressure? so the larger width of the rear (225 vs 255) require more air?


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## swchang (Oct 5, 2003)

Moderato said:


> Why not 36/38 ? 36R is actually lower then the minimum recommended pressure, and that would be a first for me, since I usually go over the manufacturers recommended pressure by 2 - 3 psi.


I'll try that, too.


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## allaboutme (Dec 22, 2003)

swchang said:


> I'll try that, too.


well if he's doing it.. i'll have to jump in too  will do next time i work on the car...

by the way moderato.. any reason you go 2-3psi above recommended?


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## Moderato (Nov 24, 2003)

Moderato said:


> Why not 36/38 ? 36R is actually lower then the minimum recommended pressure, and that would be a first for me, since I usually go over the manufacturers recommended pressure by 2 - 3 psi.


That's 36 Front/ 38 Rear. Just to clear that up.

With my past few cars I just found the recommended pressures to be a little low for my taste so usually I bump them up by 2 - 3 psi. I like the handling and wear on the tires better. But really I just take it car by car. With the 330i the recommended pressures are 32F/38R. Now these confuse me I have to admit. 38 in the rear seems like it might be a little higher then is necessary, and 32 for the front's?? That's too low, has to be. I'm running 36F/38R and I'm happy with it so far, but I am confused on this one a bit because I'm leary of droping the rears below the recommended pressure (36F/36R), but I would like to have equall pressure all around, but 36F is already firm enough for my tastes, I don't think I want to bump the fronts up to 38 and I don't want to drop the rears to 36 so I think I'll stick with 36F/38R. I think I'm getting tired now......ZZZZZZZZZZZZZZZZZZ


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## wrwicky (Jan 17, 2003)

I've had very good luck between 36 and 38 psi, cold on all 4. I agree with those who think the front starts to bounce at 38, in the back I would suprised if we don't end up wearing out the centers by running 38 or higher.


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## jsc (Sep 3, 2003)

wrwicky said:


> I've had very good luck between 36 and 38 psi, cold on all 4. I agree with those who think the front starts to bounce at 38, in the back I would suprised if we don't end up wearing out the centers by running 38 or higher.


From my analysis of 3 sets of rear tyres, it seems that for a 2000 323Ci anything above 33 PSI will wear out the centre of the rear tyres before the edges (this is consistent between a set of 225/45-17 summer tyres and two sets of 205/55-16 winter tyres).

The door plate indicates 33 PSI for the rear on a 2000 323Ci. I generally run 35 PSI all round, resigned to the fact that the rear tyres will be worn in the centre, but the car will handle a little better.


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## JAWJr (May 4, 2004)

Anybody think the lower front pressure has anything to do with the negative camber setting?


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## Moderato (Nov 24, 2003)

Anyone think that 36 psi on the rear 245/40/R17 is too low? I was thinking about trying 36psi all around, or 35For 34F and 36R, to improve wear and reduce some of the harshness and vibrations, but I don't want to negatively effect handling or risk bending a rim.


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## wrwicky (Jan 17, 2003)

I feel confident that 36 psi is fine for any sort of reasonable use. For HD use like track days, long trips with trunk and back seat full, etc, whatever the door sill says (42?)


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## Orient330iNYC (Jul 30, 2002)

after much experimenting, i ended up settling on 41PSI front/38PSI rear for daily driving with bridgestone potenza SO3s. (225F 245R). ride was harsher than stock air pressures, but it made for better handling, so it was worth it. Did not notice any exaggerated center wear on the fronts or the rears. when i replaced them with the below, the wear was even across the tread in the front and rear.

it dials out a bunch of the understeer. plus a little more tire and rim protection against NYC potholes.

after getting kuhmo ASX all seasons in 235F 255R, i lowered the pressure to 40F, 37R.

I'm running 41PSI all around on the 235/40/18 P Zero Nero M&S's on my R. ride is harsh in sport or advanced sport chassis settings, but plush under comfort.


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