Re: limits found

[AlfaNeely@domain.elided]

In a message dated 09/30/2002 9:07:15 AM Central Daylight Time, 
dloomis@domain.elided writes:



> That's an interesting diagnosis, Russ.  What about drop throttle oversteer?
> That would be my first guess with an inexperienced driver who has started
> pushing the envelope.  Power oversteer is possible in a Spider, but unusual
> on dry pavement, except in low gears and with the kind of tight corners
> found on autocross courses.
> 
> 



       Sorry, Dana, but I do not recall any large problem with "drop throttle 
oversteer."  Maybe, I always get on the brakes about the time that happens.  
Or maybe I am so used to constantly trying to keep the front wheels in front 
of the rear that I do not notice.  That would happen more with a high 
compression and / or a light flywheel and drive line, neither of which are 
allowed in my race class.
       If you let the RPM drop too much in a downshift and let the clutch 
out, then the rear end will come out rather violently.  Another good reason 
to double clutch down shifts.
       My 84 SCCA ITB spider is very tail happy.  Most corners are close to 
dirt track style with the rear end out under power.  I have a large tubular 
front sway bar from Jack Beck.  I have 1200 pound front springs and 200 pound 
rears, so the car is much stiffer in front than in the rear.  Of course, with 
the mechanical advantage of the front A Arms, the 1200 pounds springs are 
probably around 400 pounds at the wheel.
       I found the car became much more stable after setting the corner 
weights.  I have adjustable front spring perches, so it was easy to balance 
the car.  It would be ideal if both front wheels and both rear wheels had 
exactly the same weight, but that is next to impossible on a production 
chassis.  So I set the left front and the right rear combined weights to be 
equal to the right front and the left rear combined weights.  For the 
newbies, that would be like making all four legs of a table the same length.  
If two opposite legs are short, the table will be unsteady.  The same 
principal works on a race car with the corner weights.
       The other thing that reduced oversteer was to disconnect the rear sway 
bar.  This winter's project will be to build a panhard bar rear suspension 
with heim jointed upper links.  That should get the rear roll center low 
enough to make the rear more stable.
       I am also running zero toe.  Toe out will help a car turn into a 
corner, but it will also contribute to oversteer.  It is not for a rear wheel 
drive street car as tire wear will be excessive and the car will not be 
stable in a straight line.
       By the way, several guys in my ITB race class are front wheel drive.  
They all run welded up differentials.  They have mentioned that lifting in a 
corner will produce extreme oversteer.  That is handy for setting up for a 
corner, but not mid corner.


Ciao,
Russ Neely
Oklahoma City
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