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TR-6 Rear Sway-Bar

Subject: TR-6 Rear Sway-Bar
From: Jim Prettyleaf <>
Date: Wed, 29 Jun 2005 10:27:56 -0700 (PDT)
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 
 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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