I've mentioned this before, but here's what you want--in the
steering-centered position, the center of the inner tie rod joint needs to
intersect a line drawn through the pivot points of the upper and lower
suspension arm. That's ideal. The height of the rack varies the angle of a
line drawn through the center of the tie rod. This line needs to intersect
the instant center, which is the intersection of the lines extended through
the upper and lower suspension arms. Then the outer tie rod end needs to
intersect a line drawn through the upper and lower mounts for the
upright--the outer suspension pivots.
That's the ideal--you'll have zero bump steer if you do that. Corrections
like bending the steering arms, raising and lowering the rack, etc. are all
tweaks to either attain this ideal, or compensate for the inability to
adjust one of the other two parameters. You can't get zero bump steer doing
that, but you can narrow the curve and move the really bad parts past the
limit of suspension travel.
The reason why many cars have stiff front ends and limited travel is because
they handle terribly when they don't--because they either have a lot of bump
steer or a lot of camber gain. It's an empirical answer to a design problem,
and it doesn't really make the car handle like it could.
It's worth doing the work to get this right. I think 50 percent of the
reason Peyote does so well is that it's front end is so well sorted. Not
just by me, but by all the guys that owned it before--probably mostly Pat
Starr but also Bill Ames. Peyote has very soft front and rear springs, and
yet in any picture you see of it you'll see almost no body roll--that's the
roll bar being right. And you'll also see that the tire are flat on the
pavement and not sliding. The rear end is doing it's own thing--frequently
trying to pass the front, but the front end is always steering. Very smooth,
very compliant, and very predictable--right until it spins.
That's a long-winded way to say that you need a pretty narrow rack if you're
going to get even close to the inside suspension pivot point line.
-----Original Message-----
From: owner-fot@autox.team.net [mailto:owner-fot@autox.team.net] On Behalf
Of Herald948@aol.com
Sent: Wednesday, July 27, 2005 8:58 AM
To: fot@autox.team.net
Subject: RE: TR3 rack & pinion
In a message dated 7/27/2005 11:35:12 AM Eastern Daylight Time, Bill Babcock
<BillB@bnj.com> writes:
>I'd be worried about bump steer with any conversion. The rack looks a
>little long....
======
I wondered about that as well. From strictly "eyeball" / side-by-side
comparisons, it seems to me that all the Triumph steering racks, whether
TR4-6 or Herald-based, are about the same width. So I'd have to assume some
shortening of the tie rods would be needed for the narrower TR3 front track.
Yes? No?
And yeah, I also wondered about cutting the cross tube? Doesn't sound like a
good idea to me....
--Andy Mace
|