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1st Autocross

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rjbaren:
Hello, I am signed up for my first parking lot type auto cross next weekend with the local BMW club.  I have a 73 Twin Cam Special.  My tires are stock size Barum and my suspension is stock except for Spax adjustable shocks and the stock front springs were changed because they were too tall.  I think a pair of 110 lb. springs were installed but I am not sure the poundage. 
Any tips on shock settings and tire pressures?  Any tips in general?  I have only auto crossed once about 30 years ago in a stock Sunbeam Alpine.
Thanks

E Paul:
It has been a long time since I autocrossed my stock suspension Europa Special. What I remember was that I needed to reduce the rear tire air pressures to help get the car to rotate. In the sharp corners of the parking lot events, there was just to much understeer.
Just have fun!

Clifton:
Awesome that you are doing it again. I autocross too. Start of our season is Sunday. My car is a little tail heavier than most Europas due to a different engine but I run 18 psi front and 24 psi rear.  If you don't have a pyrometer, you can get some chalk and chalk about an inch long and 1/2" wide of the edge where the tread and sidewall meet and you will know if you are too low and rolling it over. Lower is better until it's too low. If you have some tall, regular all seasons maybe a few more psi but don't follow what 3000lb + car guys run.  I run my shocks the same on the street as autocross. Just enough rebound without being uncomfortable. I don't change anything. Show up, run, and drive home. If you stiffened up the front springs only and not the rear it should understeer a little more. Easier to drive than loose but if it's excessive understeer, you can run the rear shock stiffer, if they increase bump and rebound and try to reduce the push. Only change one thing at a time.

rjbaren:
Hi and thanks Clifton.  I have all season tires I think they are currently set at 16lbs. front and 26 lbs. rear pressure.  Also I checked the shock adjustment and they are set all the way counter clockwise which I believe is the least stiff.   So would those pressures and basically no adjustment be a good place to start?   

Clifton:
I would run more front pressure and a little less rear. I run "street" autocross tires and have a pretty stiff sidewall plus I run stiffer springs, 250 lb front and a large bar. My 18/24  would probably too little for you with stock camber. I think 16 psi in the front with all seasons will roll over more than you want for autocross. Maybe 22 front 24 rear cold. I would bring a pressure gauge and if you aren't close to the edge on the first run, I would lower 2 psi then 2 psi on the next run. It's easier to lower then add in between runs. Your pressure will come up too after you get heat in them so don't go by the same numbers when hot. My 18/24 is cold.  I would just make sure the fronts are being used equally the same as the rear, both at the same point on the edge, whatever that ends up at. If you know they are being used equally the same and you find the limit of slip at one end, you can go from there rather than wonder if it's pressure or spring or both.

You don't have to chalk but it is easy to see and cheap.

First pic is chalk half wiped off so you can kind of see what it looks like before and after. It is a cleaner line after a run.

Second pic is how much roll over I have.

Third pic is wifes car, street use only. If hers looked like this pic after a run I would lower it 2 psi per run until it rolled over to match the second pic of mine.

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