I just finished reading Greg Lunds article titled Competition TR-6 Handling
and have additional thoughts and questions that I would like to discuss with
other TR-6 owners, but a little background information about my car will
probably be helpful first.
I have been searching for methods to improve the balance and turn-in of my
modified 1971 TR-6. This car has a pumped-up normally aspirated 3.8 liter
Buick V6 engine, roll cage chassis stiffener, front suspensions modifications
per Kass Kastners recommendations, custom built 3 link IRS, and 48% front 52%
rear weight distribution. Front springs are British Leyland rally springs with
one turn cut-off and closed, the rear springs have a higher rate and bigger
0.62" wire diameter than the British Leyland competition rear springs which I
recall were made from 0.58" diameter wire. The car currently has a 7/8
diameter front sway-bar and no rear sway-bar. With the current configuration
turn-in is okay but not as good as I want, however the rear of the car
gathers-up from oversteer very quickly when the throttle is lifted.
My current plan for improving turn-in is to add a rear sway-bar, but I am a
little nervous about this change because I previously had bad experiences when
a 5/8 diameter rear bar was used in conjunction with the original TR-6
semi-trailing arm rear suspension, the same road springs and the same 7/8
diameter front sway-bar currently installed on my car. When I previously
installed the 5/8 diameter rear sway-bar the car was extremely tail-happy and
require forever to gather-up if oversteer was provoked. This excessive
oversteer made the car extremely twitchy which was definitely not the correct
handling characteristic for consistent autocross performance. I was still
using the stock rubber bushings in the alloy trailing arms when the car was
utilizing the 5/8 diameter rear sway-bar, and now am wondering if bushing flex
was contributing to the wild nearly uncontrollable oversteer. The current 3
link IRS has spherical rod ends everywhere; the only rubber is located in the
heavily
reinforced upper frame mounts for the Dana-Spicer model 90 differential. The
lower end of the differential mount is connected to the TRs frame by a panhard
link with spherical rod-ends, so the suspension geometry of the new IRS does
not change when cornering load is applied.
I am planning to go through the pain of fabricating the rear sway-bar and all
of the frame and suspension mountings needed just so I can determine what
happens when a rear sway-bar is used with the new IRS. If other TR-6 owners
can share prior experiences and explain how they were able to use a rear
sway-bar to improve turn-in without inducing too much oversteer I would be very
grateful for some advice.
Jim Prettyleaf
Cupertino, CA.
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