[murph-54]

I have a 335i upgraded a Procede 3 and the Dinan Stage 3 suspension package that includes beefed up anti-sway bars, springs, shocks and camber plates. The shocks ahve been adjusted to their stiffest setting (12 out of 12). Wheels are OEM 189's with Eagle Assymetrics (255 in the rear and 235 in the front). Much of the understeer that is common with the 335i has been eliminated, but I still want the car to be a little more neutral. I have been searching the forum regarding tire pressure and some seem to believe that increasing tire pressure in the rear will help while others believe just the opposite. Last time I was at the track I ran 36 psi in the rears and 33 psi in the fronts. I'm going again tomorrow and need advice. Thanks.

[PaulBailey@ltbmw]

Very nice set up!
I always like running higher pressure

[murph-54]

What would you recommend for the tire pressure in the rears and the fronts?

[nicknaz]

removed

[Josephkao]

Run higher front tire pressure like 40PSI

[DrDomer]

Originally Posted by Josephkao

Run higher front tire pressure like 40PSI

Look at treadwear patterns and you might want to borrow a pyrometer from someone. Sometimes less pressure is better too.

[nicknaz]

removed

[rsjames]

Originally Posted by Nick Nazareno

I'm not a suspension guru by any means but my gut feel says your dampers could be way too stiff on compression. Perhaps you could try to soften the front damper compression to see if that helps.

Also, what are your alignment settings? If you added a little bit of rear toe out that should help as well.

I'd be cautious with running higher tire pressure, since you are just decreasing the grip by doing that . I think it is better to maximize the contact patch and fiddle with the adjustability that you dropped a ton of money on

Yeah, what he said... You're going to have a lot more success adjusting the other stuff before tire pressures. Tire pressures are a very fine-tune adjustment.

Is the understeer on turn-in, or is it steady state? If it's on turn in, try a bit more toe-out on the front. Steady state, try more negative camber at the front. And I'd definitely try softening up the front shocks a bit.

Out of curiosity, How does the rear shocks on full stiff affect putting the power down?

[leftcoastman]

Originally Posted by Nick Nazareno

that's going to add more understeer from reduced front tire grip

I disagree.

So do they: http://www.rogerkrausracing.com/Tech...verunder.shtml

[nicknaz]

Originally Posted by leftcoastman

I disagree.

So do they: http://www.rogerkrausracing.com/Tech...verunder.shtml

Thank you for sharing.

I found a page that could be helpful to the OP
http://www.miataracing.net/car_setup...g.asp#problems

Also, I noticed the sixth row from the top describes what I intuitively thought (issue with damper settings)

However, that page's advice is the opposite of what I recommended: "Corner exit understeer/ Front shocks are too stiff in rebound." ( I had suggested the shocks were too stiff on compression)

My apologies to all for posting incorrect tech, and thanks leftcoastman for bringing to my attention

Regards,
Nick

[leftcoastman]

Hey Nick - sorry, didn't mean to sound curt.

[nicknaz]

Originally Posted by leftcoastman

Hey Nick - sorry, didn't mean to sound curt.

No apology needed. In fact thank you, because I learned something new today from reading the page you posted plus the subsequent page I searched for.

[murph-54]

Thanks guys. I have been at the track all day and ended up running 41 up fron and 39 in the rear. These are after heating up. I will check in the morning to see what the corresponding cold temps are. I took off all of the traction control and the car was very well balanced. One of the instructors riding in a new M3 came up to me to find out what I had done to my 335 because I was right on the M3 in the corners and had more acceleration in the straights so that he had to let me by.

[Arustik1]

what do you use as daily driving PSI? i have 32f 34r?

[DrDomer]

Originally Posted by westwest888

Run 30 in front and 35 in the rear cold. You can also decrease the stiffness of your suspension in the front. Do this all in stages, or you'll get an abrupt change in handling that could put you into a guard rail.

Do NOT run 40 in front like someone here said. That will push city - really bad understeer. Running 40 cold in front will heat up well over 50 in spirited and could be dangerously overinflated.

More negative camber in the front is not going to be possible without camber plates. The car will let you do about -1.0 at most.

Tire pressure is the most coarse adjustment you can make. Everything else is fine tuning, IMO.

What he said. When my "cold" tire pressures were 32 up front and 35 rear they were running 41 up front and 40 rear when I returned from a 20 min lapping session. I had lots of push. I also had a treadwear pattern that looked like I had too much pressure up front. I took out 2 psi from the fronts and the understeer improved. 30 up front sounds right to me.

[S4to335]

Originally Posted by murph-54

I have a 335i upgraded a Procede 3 and the Dinan Stage 3 suspension package that includes beefed up anti-sway bars, springs, shocks and camber plates. The shocks ahve been adjusted to their stiffest setting (12 out of 12). Wheels are OEM 189's with Eagle Assymetrics (255 in the rear and 235 in the front). Much of the understeer that is common with the 335i has been eliminated, but I still want the car to be a little more neutral. I have been searching the forum regarding tire pressure and some seem to believe that increasing tire pressure in the rear will help while others believe just the opposite. Last time I was at the track I ran 36 psi in the rears and 33 psi in the fronts. I'm going again tomorrow and need advice. Thanks.

This should help

http://www.rogerkraustires.com/TechS...verunder.shtml

wait..I just noticed that leftcoastman posted this already. BTW, leftcoastman..Brandon Kraus of Roger Kraus Racing/Tires use to do most of my alignments. I really like those guys.

[sg335]

Your style of driving and speed at which you travel also comes into play with this variable. Some of you are reporting less push with less pressure up front and others less push with more pressure up front. The best advise is to adjust your pressures incrementally both front and rear and keep a log with times and comments to determine what is best for you. You will need to spend a whole track day on this with frequent hot pitting after a few laps for recording purposes. Most R compounds work best in the +-40lb hot range. I needed to start with about 26-28lbs cold to get there. However, I would recommend starting the first session with 32-34lbs and bleed down to the desired pressures. The 335 is front heavy and increases front temps more than some other cars. I will assume that your 33/36psi were cold temps and not hot. If they are hot, you are way to low especially in front.

As for my own recommendation, I always add pressure to the front to dial out push as I am starting with low pressures to begin with. With the DA's I would play with the front rebound and compression first rather than adjust the tire pressures as I had these adjustments available to me. General rule of thumb: increase front pressure and decrease rear pressure to dial out push, but I would do the front pressures first by a few degrees and then adjust the rears before adjusting the fronts any further.

There is an interesting note in the web sites tire section under Toyo at the bottom: "Running 2# to 4# higher pressures in the front tires will reduce understeer in most cases". This assumes that you have good starting pressures. If you started with 45lb cold and ran over 50lbs hot, increasing pressure in front will increase push as there will be less bit in the front due to the decreased contact patch.

The joys of tuning a car...

[DrDomer]

A little off topic, but to illustrate a point, my TAG Kart will understeer slightly early in a race, then handle neutral, and then understeer some at the end again. What happens is the tire temps are cold and pressures are low at the beginning of the race, then tires warm up and pressures increase to where the contact patch is perfect and grip is great. As the race goes on the tire temps continue to increase, and the tire pressures get a little too high and the contact patch decreases. Guys will run Nitrogen to help, and/or adjust tire pressures so they're fast at the beginning, middle or end of the race.

So underinflation and overinflation can cause understeer, and it does depend on where you start for pressures when giving advice on dropping or raising tire pressures. Also, sometimes people think they have understeer when in reality they have improper corner entrance speeds, improper lines and improper braking (which I am guilty of).

(Obviously using kart tires to illustrate a point may not be completely valid, but I think it helps.)

[DrDomer]

[quote=sg335;3227749]There is an interesting note in the web sites tire section under Toyo at the bottom: "Running 2# to 4# higher pressures in the front tires will reduce understeer in most cases". [quote]

I think this must be for normal driving tire temps (i.e., spirited road driving?). Right? If I had increased my front pressures my contact patch would have lessened further.

[nicknaz]

Originally Posted by Arustik1

what do you use as daily driving PSI? i have 32f 34r?

I use 32f/r cold pressure all the time, including DEs. I don't bother to play around with the temps since the car generally feels fine and I don't have a pyrometer (or suspension adjustability) anyway

I feel like the understeer can be minimized by backing off when the tires start to overheat (usually 15min into the afternoon session when ambient temps are 95F).

That said, maybe I'm doing something wrong or don't have enough perspective, I find the stock car is fairly neutral and don't feel the need to change anything other than my driving skill

[sg335]

[QUOTE=DrDomer;3228081][quote=sg335;3227749]There is an interesting note in the web sites tire section under Toyo at the bottom: "Running 2# to 4# higher pressures in the front tires will reduce understeer in most cases".

I think this must be for normal driving tire temps (i.e., spirited road driving?). Right? If I had increased my front pressures my contact patch would have lessened further.

Not necessarily so. The stock camber is so inefficient at providing a proper contact patch, any standard theory regarding over/understeer is skewed to begin with. The less pressure you have, the more tire squirm/sidewall roll over. This rollover effect causes the car to transfer addition load to the outside edge of the tire and handling becomes more "sloppy". Increasing the pressure reduces this sidewall roll over and the contact patch remains more true in relation to the wheel width, and therefore handling becomes more precise and can result in better handling and less push. Use your probe pyrometer at outside, middle, and inside tread areas to get your baseline and then adjust your pressures up and down and see where the temp reside. Start with the recommended hot pressures as per the manufacturer and adjust up and down by one to two degree increments. You will never get even temps with the stock one degree negative camber. You will need a minimum of 3.0 negative to come close to even with tire inflation adjustments. I had 3.5 and came within 5 degrees on some days.

[DrDomer]

[quote=sg335;3231853][quote=DrDomer;3228081]

Originally Posted by sg335

There is an interesting note in the web sites tire section under Toyo at the bottom: "Running 2# to 4# higher pressures in the front tires will reduce understeer in most cases".

Not necessarily so. The stock camber is so inefficient at providing a proper contact patch, any standard theory regarding over/understeer is skewed to begin with. The less pressure you have, the more tire squirm/sidewall roll over. This rollover effect causes the car to transfer addition load to the outside edge of the tire and handling becomes more "sloppy". Increasing the pressure reduces this sidewall roll over and the contact patch remains more true in relation to the wheel width, and therefore handling becomes more precise and can result in better handling and less push. Use your probe pyrometer at outside, middle, and inside tread areas to get your baseline and then adjust your pressures up and down and see where the temp reside. Start with the recommended hot pressures as per the manufacturer and adjust up and down by one to two degree increments. You will never get even temps with the stock one degree negative camber. You will need a minimum of 3.0 negative to come close to even with tire inflation adjustments. I had 3.5 and came within 5 degrees on some days.

Thanks for info. Do our stock runflats have less of this sidewall rollover issue than regular non-runflat tires? I haven't upgrade my rubber yet.