Hmmm, I didn't write the last paragraph correctly--moving the upper pivot
point inward substantially (about an inch) and lengthening the arm about a
half inch raises the roll center. Bump steer is mostly induced by the
relationship of the steering rack to the steering arm as the suspension
travels. When you model the TR3/4 suspension and lengthen the upper arm
the amount of bump steer is reduced. I never could figure out exactly why.
-----Original Message-----
From: Bill Babcock
Sent: Thursday, December 19, 2002 1:30 PM
To: 'Mike Rose'; fot@autox.team.net
Subject: RE: camber
Shortening the upper arm is a common modification, but it causes other
things to happen that you need to take into account. You're reducing the
radius of the upper arm, which means that your camber will vary as the arm
travels (probably not a big deal if you have a lowered car and stiff
springs). It will also change bump steer and can change caster if you're
not really careful in your fabrication. If you really want to play with
your suspension I suggest you get some modeling software--it's cheap. I
really like the software from www.auto-ware.com called "front suspension
geometry pro" it's fun to play with and it's $119. It's easy to use though
the measurements take forever. I also like their "tire temp analyzer".
I also have SusProg3D Designer from www.SusProg.com which is a little
more expensive ($150) but very cool and you can download a demo version
free. Any of these products take time to use, because you have to
establish a reference line and take a zillion accurate measurements. But
it takes a lot less time and money than doing cut and try--and you can run
the software in your warm, dry kitchen.
My original modifications for my TR3 were made with an illegal copy of
software from one of the big racecar engineering companies upon my solemn
promise to erase the copy when I was done with it. It was available for
sale for five figures. It had no real modeling capabilities--it just built
tables. By comparison this hundred buck stuff is far superior, and I got
almost exactly the same answers when I entered my original data into
Susprog.
If you decide to modify the upper arm, and your regs aren't strict, I
suggest incorporating adjustable heim joints so you can tweak both caster
and camber. Moving the upper arm inwards is actually a better
modification, and lengthening the arm reduces bump steer and raises the
roll center.
-----Original Message-----
From: Mike Rose [mailto:lytspeed@hotmail.com]
Sent: Thursday, December 19, 2002 1:00 PM
To: fot@autox.team.net
Subject: camber
Vizard's "Tuning Standard Triumphs" states that moving the lower
suspension pivot bolt of the TR4 0.17" outward will result in reducing
camber by 1 degree. Will this also have the same amount of camber
decrease by shortening the upper a-arm by the same amount (shortening
upper a-arms by 0.51" resulting in a decrease of 3 degrees)? Mike
|