First Autocross with Ventus Rs3's

[joe1602]

My son (teen ti) and I will be competing in our first autocross of the season this weekend. We have upgraded to the Hankook Ventus Rs3 tires and are at a bit of a loss as to where to start with the tire pressures. The ti is a bone stock 99 M-Package with no upgrades other than the tires. Last year we ran slightly lower pressures in the front than in the rears, like 38f 40r and had many problems with the front end understeering. The tires we used were very old Bridgestone's with no tread on them, they were junk. We are wondering if some of the understeer problems will go away with proper tires on the car and if we should just be starting with the same pressures (say 40) all the way around. Unfortunately in our region, we don't have any testing days so we are starting they season a little in the dark with these tires. Any information and advice would be greatly appreciated. The tires are 225/50/16. Thanks!

[spidertri]

For autocross I run my Z2s at 36f 34r and it seems to work well. However, my car is closer to STX than stock. Stock suspension is designed to understeer, it's safer for the average driver and less of a liability for BMW.

My car understeered like crazy until I put on camber plates and got -3deg in the front, then it drove like a wonderfully different car.

I would start with rear pressures higher than the front. Also, pushing the car that hard without camber plates could tear the front outside edges of the tires up fairly quickly. If you have to stay in stock try and get a rear sway bar from a z3 m, 19mm, and run that. That should help loosen up the rear end and make the front feel better.

[joe1602]

Dave, thanks for the info. That gives us a good place to start from. Is there any way of putting negative camber in the front without camber plates? We are planning to run the whole season in G stock and then do some suspension mods over the winter (depending on finances) and possibly run in stx or fsp next year. We are hoping for the camber plates next year, I just don't really want to trash the new tires this year. Thanks again for the help & will post, maybe with a video, on how we do Sunday.

[spidertri]

There are factory "crash bolts" that allow a little bit of camber adjustment in the front, maybe 0.5deg or so, better than nothing. I believe they are the only stock class legal option.

Part #5, "camber correction bolt"
http://www.realoem.com/bmw/showparts...21&hg=31&fg=10

There have been reports that the bolts can loosen under hard driving and lose the alignment. I think if you retorqued them before each event they would be okay. You could also mark them with a paint pen to see if they slip.

Bimmerworld sells camber shims for the lower front struts, a better option than the bolts, but probably not legal for the class. Since you're running a stock tire size the shims would be okay. When you run a wide 245 or 255 you have to worry about tire to strut clearance when using the camber shims because they tilt the kingpin towards the strut.

[joe1602]

Dave, Thanks again for the info. I thought I remember reading somewhere that you could put a few washers somewhere in the bottom half of the hub assembly to increase the negative camber but I cant seem to find the article. Maybe it was the shims you were talking about. Those are all great things to look into for the rest of the season. Thanks again for all the help, we greatly appreciate it!

[slade13]

How well are those shims on a street driven ti? I may need a little adjustment because i have springs of of a sport ti that I'm putting on.

[spidertri]

Shims only add negative camber. Sport springs aren't going to lower it much, the biggest concern is incorrect toe which will kill tires way faster than neg camber will.

[joe1602]

Had a pretty good weekend on the new tires. My son & I finished 2nd & 3rd in G Street. I was .4 behind him and he lost to a 2015 Volvo V60 T6 (which has over 300HP) by .018 of a second! Still experiencing the same pushing with the new tires but we are going significantly quicker than before. I guess when you really push the car to the limit, even with good tires, its handling characteristics still show themselves. I think we are going to try the camber shims to see if it helps some. What we really need is a whole suspension overhaul! (But, of course, we have to wait for the financing to become available)

[joe1602]

http://www.youtube.com/watch?v=KFYALNk64iM

Check out this video my son (teen ti) made of our autocross last weekend. He of course used his best run and he used my second best run. (OH well he says, then you do it). He had his fastest run in the afternoon session with all the other g-stock cars but me, beating the ford focus st that was the pax winner in the previous autocross. The course was then changed because it was breaking up in one of the turns and all of those times were disallowed. That was very disappointing for him because he beat the focus outright on a power track. I was disappointed also because I felt I had a little more to get out of the car & might have beaten him also. The tires were working great in the warm weather and we had installed the largest of the camber shims which also helped with the cars pushing problems. I then started fiddling with the tire pressures in the afternoon and the car was starting to hook up even better. Bummer but we have another solo this weekend in our home (Glen) region so we will see!