Bill
Thanks for the reply. ANY data you might still have will be
appreciated. I think I have the front down . All done by trial AND error.
Adjustable Aurora joints are the basic first step in Full prep SCCA E Prod.
The hope of going to full tube, long arms is another matter.
It's the rear that's my current problem.
I'm setting up to run 2"f ,3"r ride height. I would like to run 2" f & r
but I can't get around the rear bump steer problem. What I really want to
know is : Having dropped the ride from 6+" to 3" the rear arms geo. is way
off. I have been correcting it with the brackets ...Flipping on & on & on &
ON. My thought is that these brackets need to be raised the same amount
the chase is dropped. Into the cockpit if need be. (Legal in Current SCCA
if covered by metal.) This would (in my way of thinking) keep the Geo. the
same as far as a pivot point. Input?
Name the book I probably have it. In Fred Puhm's book "How to make
your car handle" it gives an illustration of our IRS suspension. I just
don't have the math background to figure it out and I haven't found any
software that has IRS / Trailing Arms in it's program. I would suspect with
the 914 & 911 having a similar type trailing arms, software would be
available...not the case.
David Wingett
Subject: RE: Lower A arms & geometry
> I did, spent about two days fiddling with software that didn't belong to
> me. I started out by doing all the measurements required--that takes a lot
> of work because you need to get it all very accurate. Then I ran the
> software and was so shocked at the results that I went back and measured
> everything again. Basically it told me that TR3's shouldn't be able to
> turn a corner at walking speed without flipping on their side. A slight
> exaggeration, but the numbers look really bad. The roll center for the
> front end is about 4 feet underground, bump steer input is huge, there's
> hardly any caster, camber varies greatly as the arm travels. I don't
> remember specifics, I think I wrote a long email to the list that detailed
> them, but I don't have a copy. I did find that many of the worst faults
> can be corrected, and I did so--my cheater TR3 handles wonderfully. But if
> you are planning to vintage race, you need to be very careful. I built an
> adjustable upper arm (heim joints on front and back so the overall length
> as well as the caster can be adjusted) and moved the upper arm pivot point
> about one inch inboard. Raised the steering box about a half inch. Short,
> stiff springs to lower the car and reduce front end travel (no way to
> completely eliminate the varying camber) and lots of rebound damping. and
> of course the usual sway bar, super-soft rear springs, etc, etc. Most of
> the standard stuff that people do to make TR3/4 handle is in the right
> direction.
>
> So now I have a TR3 that corners as flat as a formula ford, does lovely
> controlled drifts without understeer, and is not welcome at any vintage
> event except SCCA, where the only thing they require to be authentic is
> your entry fee.
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