If it were only that easy. Other stuff happens, for example, if you lower
a car by shortening or weakening the springs then the suspension arms
angle more upward (or less downward depending on how you want to look at
it). Moving the rack up changes the relationship of the rack to the
inboard upper and lower suspension fixing points and the relationship of
the tie rods to the steering arms. That will change the amount of camber
angle variation as the suspension travels (it will probably increase it,
but there is no way of saying for sure). You might wind up with way more
bump steer at the bottom of travel than at the top (or vice versa), which
makes for interesting handling differences, especially when one wheel
travels up and the other travels down against the resistance of the roll
bar. It will also change the amount of tire scuff induced by differential
camber (front wheel to front wheel) since that will change too. You might
lengthen or shorten the tie rods to try to compensate, but that will
induce a whole 'nother cycle of unintended consequences.
I started getting serious about modeling this stuff when I saw how many
things change when you tweak anything in a front suspension. Most of the
time people get their suspension to work by stiffening the front springs
to the point that it only travels when you hit a pothole at 85. That's not
the best way.
When you model a stock Triumph TR3 front suspension and put it through a
roll/bump you can't help but wonder how anyone can drive one to the store,
much less race one.
-----Original Message-----
From: John Kipping [mailto:johnkipping@inet.net.nz]
Sent: Thursday, January 23, 2003 1:26 PM
To: Larry Young; fot@autox.team.net
Subject: Re: Suspension/Handling Questions
I'm not an expert on bump steer but.........AFAIK the whole steering rack
should be straight in its normal rested state so that as it moves with the
suspension the effective length change is very small. Lowering a car would
then suggest either the steering rack has to be raised or the the steering
arms effectively lowered so the inner ball joint assemblies are again in
line with the rest of the rack and parallel to the road. No idea how you
do it though. John Kipping
----- Original Message -----
From: "Larry Young" <cartravel@pobox.com>
To: <fot@autox.team.net>
Sent: Friday, January 24, 2003 4:33 AM
Subject: Suspension/Handling Questions
> I've been doing a lot of work measuring and analyzing the suspension
> in my TR3 race car. I've spent quite a bit of time going through the
> archives. I can't say that I've read every post, but I think I have a
> pretty good idea of what has been posted. My questions are:
>
> 1. I've got a ride height (to bottom of frame rails) of about 4 1/2
> inch in front and 6 inches in back. What is the stock TR3 ride height
> and is it the same in front and back, i.e. frame rails parallel to the
> ground. What ride heights do most TR3 race cars have front and back?
> I know lower is better, but how low can you go?
>
> 2. I appear to have a horrible bump steer problem, with toe out
> increasing on a bump and decreasing with droop. To correct this I
> believe either the steering arm and idler arm must go down or the
> steering lever attached to the vertical link must go up. I'm thinking
> heating and bending the steering lever will be the easier approach.
> Is this the right thing to do? Do I have to worry about hardness of
> the arm? Any suggestions will be greatly appreciated.
>
> Larry Young
> Forever Young Racing
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