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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Tracking, Autocrossing, Dragstrip, Driving Techniques > Need Autocross advise, tire wear/suspension setup



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      05-21-2012, 08:23 AM   #1
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Need Autocross advise, tire wear/suspension setup

I participated in my second Autocross yesterday. Although it is organized by the Sacramento Porsche Club there are quite a few BMW's present. My car is a 2011 335d and is doing remarkably well and earning some respect. I think it is surprising a few folks how well a 4 door diesel can hang with some 911's, Boxster's, Caymen's etc.

Anyway, the issue I'm having, is that my front tires are rolling over quite a lot. I compared to some other cars there and they don't show nearly as much wear around the front edge. I understand that my car is front heavy and that this is to be expected, but I like to know from the more experienced autocrossers what I could do, as far as tire pressure and camber/suspension goes, to improve this. I'm running stock sports suspension with 19" Hankook V12's, 40 PSI. I would like to not have to replace the tires after 2 or 3 events and get to use the rest of the tire a bit more for regular street use.

Any help/advise would be appreciated.
Thanks.
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      05-21-2012, 09:50 AM   #2
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Is 40 the cold pressure value?

Unfortunately, the car's suspension is set up for more daily driving than autocross. Heck, with all the tight turns in an AutoX, the car will behave better on a road track.

Basically, you want to utilize as much contact patch from the tires as possible. Check where the tire is wearing to determine how much you need to adjust the vehicle.

Some off the top things without knowing anything further -

Increase tire stiffness
Increase negative camber
Neutral Toe
Increase roll stiffness (thicker roll bars)
Lower and stiffen suspension (i.e. coilovers)
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      05-21-2012, 12:28 PM   #3
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Quote:
Originally Posted by anerbe View Post
Is 40 the cold pressure value?

Unfortunately, the car's suspension is set up for more daily driving than autocross. Heck, with all the tight turns in an AutoX, the car will behave better on a road track.

Basically, you want to utilize as much contact patch from the tires as possible. Check where the tire is wearing to determine how much you need to adjust the vehicle.

Some off the top things without knowing anything further -

Increase tire stiffness
Increase negative camber
Neutral Toe
Increase roll stiffness (thicker roll bars)
Lower and stiffen suspension (i.e. coilovers)

Yes, 40 is cold pressure value. The tires are wearing heavy around the edges (only the fronts) about a 1/4" passed the line that divides the side wall and the tread. I'm attaching two pictures, one of the front and one of the rear, so you can see the difference in wear.

I'm kind of leaning towards adding negative camber. Do you know what the stock settings roughly are and where I should start going? How does it affect all the other handling?

Stiffer roll bars would be the next best thing and/or AutoX tires. I don't want to spend too much, so coil over is not really and option. I'm leasing the car and only have another 1.5 years left. Not sure if i will keep it after that.

Thanks for your help!
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      05-21-2012, 01:04 PM   #4
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One thing I should mention, since you said that this car would do better on a track.vs AutoX. The event I went to, and plan on going again, is on a fairly large lot. Actually got in to 3rd gear twice at end of two straights. Granted the diesel tranny does not hold gear and will up shift when close to red line. Never the less it was probably close to 65 mph at the end of those straights and the corners leading in and out were pretty long sweepers.
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      05-21-2012, 07:52 PM   #5
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Quote:
Originally Posted by Sauber F1 View Post
I participated in my second Autocross yesterday. Although it is organized by the Sacramento Porsche Club there are quite a few BMW's present. My car is a 2011 335d and is doing remarkably well and earning some respect. I think it is surprising a few folks how well a 4 door diesel can hang with some 911's, Boxster's, Caymen's etc.

Anyway, the issue I'm having, is that my front tires are rolling over quite a lot. I compared to some other cars there and they don't show nearly as much wear around the front edge. I understand that my car is front heavy and that this is to be expected, but I like to know from the more experienced autocrossers what I could do, as far as tire pressure and camber/suspension goes, to improve this. I'm running stock sports suspension with 19" Hankook V12's, 40 PSI. I would like to not have to replace the tires after 2 or 3 events and get to use the rest of the tire a bit more for regular street use.

Any help/advise would be appreciated.
Thanks.
Either upgrade to a better tire like Dunlop Direzza Z1 Star specs or Hankook RS3's, Toyo R1R's... Etc... or pump up that front tire some more. I don't know what the max pressure is for the V12's since I don't run them, but I autocross with a square setup of Z1 Star specs at 255/35/18 and I run the fronts at 45 cold and the rears at 42 cold which provide just about the perfect amount of rollover for my driving style.

From the picture you definitely need more pressure, and don't the V12's have a significantly soft sidewall?
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      05-21-2012, 10:58 PM   #6
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Quote:
Originally Posted by SpeedOften View Post
Either upgrade to a better tire like Dunlop Direzza Z1 Star specs or Hankook RS3's, Toyo R1R's... Etc... or pump up that front tire some more. I don't know what the max pressure is for the V12's since I don't run them, but I autocross with a square setup of Z1 Star specs at 255/35/18 and I run the fronts at 45 cold and the rears at 42 cold which provide just about the perfect amount of rollover for my driving style.

From the picture you definitely need more pressure, and don't the V12's have a significantly soft sidewall?
Thanks for your input. I'm not sure if the V12's sidewall is considered soft. I suppose judging from this you might be right. When I got them over a year ago, I was not considering that I would AutoX them.

I already thought about the Hankook RS3's. So what happens if I use any of the tires you mentioned? Do they roll over less because they are stiffer? Ultimately I like to get a set up that does not ruin the tires in a couple of AutoX events. What kind of live expectancy can I get out of a better tire?
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      05-22-2012, 03:46 AM   #7
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Wow, you use 40s cold? I run 32/34 HOT on the track, lol. If you cut down the tire pressure you will have less rollover and better traction, shaving about (depending on size of course) 1-2 seconds of your run. Just remember to pump them up for the ride home for better gas mileage. It has hard to adjust certain things for an autocross setup based on a stock setup. Rear camber can be dialed in but won't do very much good as compared to on a road course; front camber will make all the difference (need camber plates).

Basically tire choice is everything. If you want to attempt to make the tires last long get them heat cycled so they will at least wear a little more evenly than before. If you have any more detailed questions shoot me a PM.
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      05-22-2012, 09:23 AM   #8
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it's a combination of lots of things.

grip of the tire
footprint of the tire
stiffness of the tire
geometry of the suspension while loaded

I state in general track vs. autox, because the higher amount of tight turns in autox. Even if the particular course has higher speed sweepers, the majority of the turns are unsettled tight radius turns with higher loads on the outside front corner due to transitional turn forces.

Ultimately, changing the specs on your vehicle will reduce the daily driving life/comfort on the tires.

Track spec tires - increase wear
Higher camber settings - increase irregular wear
Anti-roll - stiffen suspension
etc.....

Ventus V12 are not track tires. Upgrading them will help.
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      05-22-2012, 11:02 AM   #9
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turbOmike

I appreciate your input. I'm surprised about your TP recommendations though. Most everybody else is suggesting higher TP and in general if the tire rolls over it is a sign that TP is too low. Maybe track is different than AutoX in that regard. I would imagine that the tires have a tendency to roll over more in an AutoX than on a track because the turns are much tighter. Sounds like front camber plates would help a lot.


anerbe

I guess it would be a compromise changing the front camber for daily driving, but if were to do 4-5 AutoX per year, which wears the outside corner of the tire, then having negative camber for the regular driving would not necessarily shorten the life of the tire, as that would probably still take longer to wear the inside off.
Thanks for your advise.

From what I'm reading so far, changing to a different tire would obviously help, but adding camber plates first, would still allow me to use these tires a couple more times and would still be beneficial with a better tire.

One more question. I'm running on 19" aftermarket wheels, but could use the stock 18's" for AutoX. All things being equal, would there be a benefit choosing one over the other. The 18" rubber is obviously a bit cheaper.
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      05-22-2012, 03:23 PM   #10
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Quote:
Originally Posted by Sauber F1 View Post
Thanks for your input. I'm not sure if the V12's sidewall is considered soft. I suppose judging from this you might be right. When I got them over a year ago, I was not considering that I would AutoX them.

I already thought about the Hankook RS3's. So what happens if I use any of the tires you mentioned? Do they roll over less because they are stiffer? Ultimately I like to get a set up that does not ruin the tires in a couple of AutoX events. What kind of live expectancy can I get out of a better tire?
The more extreme summer tires (Hankook RS3, Yokohama Neova AD08, Dunlop Direzza Z1 SS, etc.) will have stiffer sidewall than the V12, so they'll roll over a little less. In addition, the shoulder blocks on these extreme summer tires are more squared than the rounded shoulder blocks on the V12. So after the same amount of runs you put in at this event wouldn't result in the wear pattern as you have in your V12.

I don't run Hankook RS3, instead I run Yokohama AD08 255/35/18 square. I have about 12k street miles, 20+ autox runs, and 3.5 track days on the tires before I had to replace all 4. The RS3 probably won't last as long though.
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      05-22-2012, 03:34 PM   #11
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Quote:
Originally Posted by turb0mike View Post
Wow, you use 40s cold? I run 32/34 HOT on the track, lol. If you cut down the tire pressure you will have less rollover and better traction, shaving about (depending on size of course) 1-2 seconds of your run.
Well, your setup is for tracks. OP is asking about autox setup. Generally, tire pressures are set higher for autox setup. 40 cold doesn't sound out of the norm especially for a heavy car like the E9x 335i AND with stock suspension. I normally run 45-48 front, 40-42 rear cold pressures in my Yokohama AD08 for the autox. For tracks, obviously I lower them to about 38/32 HOT.
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      05-24-2012, 08:36 AM   #12
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Also be aware when you do get new tires about the treadware, if you run with the SCCA... There is talk about making a change to the minimum treadware rating for Street Tire classes from 140 to 200. The 'Kook RS3's are at 140, but the current star specs are safe at 200, although a new revision is due out soon for the star specs.
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      05-24-2012, 09:05 AM   #13
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Quote:
Originally Posted by vwong View Post
The more extreme summer tires (Hankook RS3, Yokohama Neova AD08, Dunlop Direzza Z1 SS, etc.) will have stiffer sidewall than the V12, so they'll roll over a little less. In addition, the shoulder blocks on these extreme summer tires are more squared than the rounded shoulder blocks on the V12. So after the same amount of runs you put in at this event wouldn't result in the wear pattern as you have in your V12.

I don't run Hankook RS3, instead I run Yokohama AD08 255/35/18 square. I have about 12k street miles, 20+ autox runs, and 3.5 track days on the tires before I had to replace all 4. The RS3 probably won't last as long though.
If I were to get 12k miles plus 20 autox runs out of a set of tires I would be happy.
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      05-24-2012, 09:55 AM   #14
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Quote:
Originally Posted by Sauber F1 View Post
If I were to get 12k miles plus 20 autox runs out of a set of tires I would be happy.
I just run mine during the summer (stock wheels during the winter with a set of all seasons) and I get about 15k and about 50+ autoX runs but no track days. It ends up being about one set a year, and yes I drive a lot... lol
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      07-23-2012, 01:26 PM   #15
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Follow up:

Yesterday was my first autocross since I installed new Yokohama Advan AD08's on my car. They worked very well and held up great in the heat. It was 105 deg and they didn't loose performance.I continued to shave off a few tenths on every run, unitl the end. Allthough I did spray them down between runs to try to keep them from overheating.

In retrospect I now realize that the suspension work and camber plates didn't really help all that much, mainly because the Hankook V12's I had on the car before were at the end of their live. Whatever I gained in suspension dynamic, I gave up in the tires going bad.

The camber plates are great for preventing the outside edges from excessive wear, but I'm not really sure that they improved my times all that much. It was still a necessary modification, or the tires would be shot after a couple of events, which would get expensive quick with these tires, they weren't cheap!

Anyway, it's obviously hard to say precisely, but I'm guesstimating that these tires are about good for 1.5-2.0 seconds on a 1 minute autocross lap, over a Hankook or equivalent tire. All in all it's just confirmation that tires do make the biggest difference, after the driver of course.
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