Date: Fri, 7 May 1999 14:15:51 -0700 (PDT)
From: Wes Shew <schumi@vcn.bc.ca>
<< I'm pondering how swaybars can make a car turn faster lap times. Let's say
you upgrade to a larger front bar on a RWD car that normally oversteers
at the limit. In theory you will lessen oversteer. Is this because the
front end will begin to understeer before the rear oversteers. OR, is the
traction/cornering limit (friction circle) of the rear actually increased? >>
I have read alot, and also did alot of tuning with the chassis on my car,
which is now a bit beyond SP legal.
Anti-roll bars serve at least two functions. One is to control where weight
is transfered, and the other is to limit body roll. That handling of the car
can be altered greatly by changing roll stiffness at either or both ends.
In a perect world, where the tires stay at the ideal angles to the road,
changing the roll stiffness ratio front to rear does exactly what the text
book suggests. More roll stiffness will force the outside tire to take more
load and lose traction before the other end of the car. So the big front bar
will make the car under steer more, or over steer less, whichever was the
case before the change. But the reduction of body roll can actually make the
car have more grip at both ends. In a solid rear axle car, the rear tires do
stay very near straight up, but the independant front will have the tires
lean almost as much as the body. Reducing the body lean then keeps the front
tires closer to ideal angles, and even with the greater weight transfer, they
could gain total grip.
Even if this is not the case, max cornering force will increase when the
amount of weight transfer from front to rear is ideal. If there is too much
weight transfer at one end, it will have less then ideal grip. Increasing the
weight transfer at the other end of the car wil take some load off the
outside tire of the bad end, and allow the inside tire to do more of the
work. So the end that was loosing grip first can increase it's grip by adding
a anti roll bar stiffness to the other end.
I tried taking it to the extreme, and found there is definately a practical
limit. I tried HUGE anti roll bars on a rear drive car and ended up with a
car that was very hard to drive at the limit because any ripple in the
surface caused the tires to slip across the surface. The car was balanced,
but nervous, all the time. So far this year, stiffer springs and softer bars
seems to be much easier to drive at the limit. My (OPINION) is that anti-roll
bars should just fine tune proper spring rates. The shocks dampen the same
for spring or roll movement, so having a big difference in spring and roll
rate makes it hard to dampen correctly. I feel this was what caused my odd
handling last year. It feels far better now.
Gary M.
STU sure is fun.
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