Corner Balancing - Inputs ??

[porschelou]

Spent the weekend working on the car getting ready for VIR. 86 325e (b34/M30).
First time we have corner balanced it. We figured it would be a little front heavy with the M30 (we installed it in pos 3 to help with the CG)

Here are the specs (sways unhooked, driver in the seat, 3/4 tank fuel):

Before --
Weight: 2761lbs
LF 842 RF 740
RR 584 LR 595

Added a 15mm pad under the LR coil -

LF 805 RF 777
LR 620 RR 561
Cross Weights
LF / RR- 1366lbs 49.4%
RF / LR - 1398lbs 50.5%

What do you think?

[Jb325is]

That should be pretty good for VIR. We usually run 50-50.5% there. Are the first weights the initial numbers?

[porschelou]

Sorry - yes the first numbers are the before num's.

Glad to get some re-assurance I'm not totally screwed up. Can't wait to try it out. We have a fresh 3.91 LSD (40%lock) and all of the leaks fixed - we are ready ( hopefully)..

Thanks

[jlevie]

The cross weights are good, but the car will be considerably more tail happy than a normal E30.

[cwbaader]

Those are not cross weights. You need LF + RR= 1425

and RF + LR= 1338...so you have almost 90 pounds of wedge in the car...going to turn left like crazy. What you really want is the two to be equal. After you get them equal, attache the sways so they do not preload the chassis.

[NigelStu]

^recheck your math. Look at the pics, #s are correct with 48% -> 50.5% for before/after.



A touch over 50% should be good for VIR since it is mostly RH turns, BUT if you find the car is a bit loose/unstable coming onto front straight or 1 and have to wait to go full throttle, you may want to drop a bit. a 10 mm spring pad on that left rear will likely put the car right about 49.5-50% and give the car some stability in those high-speed corners. Be ready with different spring pad thicknesses if there are any handling issues.

You may want to also check the car with full tank and near empty tank so you can understand how the corner and FR/RR balance will change throughout a stint (although the data I have has shown minimal cross-weight change with fuel load changes). Keep in mind that as the fuel is used up, weight balance is going to move forward and you'll get more oversteer.



Are you running the rear bar? I am not on our car, and that is with the M20 in there, car has a very nice balance, a bit understeer at start of stint that changes to about perfect by half tank and stays great through end of stint.

An option if you find the car has too much oversteer, even without rear bar, is to raise the front with some extra/thicker spring pads

[jlevie]

I should have looked closer, by bad. Cross weights, as cwbaader pointed out, are LF/RR and RF/LR. I get 51.5 LF/RR and 48.4 RF/LR. Which is very not good.

[porschelou]

Man - I messed up those numbers. Not sure what I was thinking last night. I had the corners wrong in my text. I fixed them. The pic was correct since it was of the display.

Jlevie - I'm guessing you were using my wrong positions. I hope :)

I have a vert front sway and stock rear bar. There was no pre-load on the fronts but just a little on the rears (just using stock end links). The car has always been bad in left turns ( my LSD was dead so not sure if that was causing this issue). I have a new 3.91 LSD for this race with 40% lock-up.

I do have different pads thicknesses if I need to swap.

This is first time I have used scales - thanks for educating me..

[cwbaader]

Remove one of the spring pads from the RF. McMaster has all the pieces you need to make adjustable end links...consider it.