John,
Why do most race cars use either a locked rear end (NASCAR) or some sort of
torque-biasing using like the Torsens on Champ cars? If it was just a matter
of good chassis setup I'd think that they would have the money and smarts to
handle it.
In my case, it's possible that using race car level stiffness in the springs,
and getting away from sway bars, would give me more traction on the inside of
the car. However, I'm driving a compromise. It has to be streetable for
friends and family as well as fast on the track, so all that spring would be
too stiff. I can't lower its center of gravity much for the same reasons, and
I can't stiffen the chassis with subframe connectors because of the rules. So
sway bars seem a necessary factor. When I changed sway bars, the cornering
speed went up, I did measure that much. All I could do to fix "the traction
problem" was to balance the rear vs. the front. More rear bar vs. front has
shown to plant the inside tire somewhat better. Maybe not as much as doing it
all with springs, I don't know. I do know that a professional racing team
using this model of car had both heavier springs and FAR larger sway bars. Me:
F 24mm, R 29mm. Them: F 63 mm, R 83 mm.
My admittedly limited visualization of what happens in a corner: When weight is
transferred outwards, there will be a point after maximum cornering is no
longer needed where you want to use forward motivation as well as some portion
of cornering force (maybe say 1:30 or 2:00 on the friction circle). The outer
driven wheel is being additionally loaded with transferred weight so can
withstand more transmitted force than when in a straight line. The inner
wheel, at about the same slip angle, less weight, less friction available. If
the available torque at that point exceeds what the inner wheel can transmit,
it spins, rather than the car accelerating.
If you then add a LSD then it allows you to take advantage of any margin that
is in the outer tire's friction circle, independent of the inner wheel. It
seems likely that there will sometimes be this extra slack present.
PaulT
-----Original Message-----
From: John F. Kelly Jr. [mailto:76067.1750@compuserve.com]
Sent: Thursday, May 15, 2003 5:27 PM
To: Tibbals, Paul
Subject: RE: Atwater questions
-------------------- Begin Original Message --------------------
Message text written by "Tibbals, Paul"
" Or do you think that it doesn't slow down a car much?"
-------------------- End Original Message --------------------
I don't think an open diff slows down a car at all.
I think that in many instances a limited slip is installed as a band aid
for a problem and the problem itself is not addressed.
That problem is the inside wheel spinning. What it's also doing is
NOT applying its traction force to the road. Installing a limited slip
still leaves that inside wheel doing no traction service. That's why, in
many cases, an LSD is a band aid. It makes both wheels spin together but
one isn't, essentially, touching the ground.
Fix the traction problem FIRST. Then you might find out you don't
have to spend a ton of money for a Quaife because BOTH wheels will apply
their driving force to the ground.
That's about as simple as I can make it.
--John Kelly
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