It's basically just compromises, and the front end is not much better than
the rear. To make a front end with no bump steer you need the ends of the
tie rods to intersect an imaginary line between each of the upper and lower
suspension pivots, and the angle of the tie rod to be such that it meets at
the instant center of the upper and lower arm (instant center is the point
where imaginary lines extended through the axis of the suspension arms
meet). That's hard to accomplish with a rack and pinion steering system with
ball joints, never mind a lower trunnion that has it's vertical rotation
point in a different plane from the horizontal rotation plane (that doesn't
happen with a simple ball joint).
Bump in the back comes from the same problem--the location of the arms
relative to suspension travel.
-----Original Message-----
From: owner-fot@autox.team.net [mailto:owner-fot@autox.team.net] On Behalf
Of LOddTR@aol.com
Sent: Thursday, March 04, 2004 3:05 PM
To: fot@autox.team.net
Subject: TR IRS Thoughts
Winter has caused me to ponder numerous "what if's" on the rear end set up
of my TR 250. We all know the issues with toe-in gains and the resultant
need for a firm spring and shock set-up. Being a novice in suspension
geometry, I was wondering why Triumph, and other manufacturers didn't use a
modified front suspension.
The unequal length A arm design certainly would eliminate the toe gain and
provide a stable platform for adjustment. A vertical link similar for that
in a Spit or GT 6 would be needed of course, and some redesign of the rear
frame section and parcel shelf. Is there a design issue that prohibited
this? Did the need for on road safety mandate the toe-in gain? Did any
modified racers avery create something like this? Or, and probably likely,
am I all wet?
I can't make these types of changes on my car and remain legal but the
thought does interest me.
Leo Oddi
TR 250 #68, SVRA, VDCA
|