On Tue, 3 Sep 2002, Jim Hurley wrote:
> Hello,
>
> On Tues. 3 Sep 2002 at 8:25 Shawn Loseke wrote:
>
> ....
>
> >A stock TR6 can be quite a handful when pushed to the edge. But it has
> >been my experience that the handling foibles inherent in a stock set up
> >can be easily cured without a major compromise in ride comfort.
>
> >Have others had similar experiences?
>
> Care to be more explicit? What do you mean by "a handful when pushed to
> the edge", what are the foibles, and how are they easily cured?
Without going into a lot of detail, I would like to offer the following.
Suspension movement is dynamic. The movement of the suspension relative to
the body is predictable, but in the stock configuration, the body motion
is considerable. Not nearly as considerable as a Cadillac, mind you, but
when this is "tamed" the car will handle in a much more predictable
manner.
When you push a TR6 to the limits of adhesion, the car is actually quite
predictable. What complicates the matter is that driver input can change
at inopportune times as far as the suspension is concerned.
For example: you enter a corner fast. Maybe too fast, but fast
nonetheless. The front end will "push" a bit and when the driver detects
this will either turn the wheel more (probably with no major effect on the
car's motion - this is designed into most passenger cars to keep you from
getting yourself into trouble!) or will lift the throttle. At this precise
moment, the rear of the car will try to swing out, part of this motion is
due to weight transfer from the front to the rear and part of it is due to
camber/toe change which is the result of the "semi-trailing arm" rear
suspension.
Some people call this the "triumph twitch". I've driven a bunch of cars at
the limit. This twitch is really not unique to Triumphs.
At any rate, the question is: How do you fix it?
Simple. Well, not really simple, but bear with me. If you increase the
"roll stiffness", you will get less camber change. This helps keep the
tire contact patch uniform. But you also get the potential added benefit
of less rear suspension toe change and this also helps a lot because the
car will tend to track in the same direction or very close to it.
Believe me, it takes really small changes of toe and camber to make a huge
difference in the feel of the car. So, if you tweak the suspansion to
result in a degree or two of dynamic toe change you can go from "tail
happy" to neutral.
How do you get there? First off, you play with sway bars (assuming the
rest of the suspension is okay). Go to a bigger bar in front first. This
is a "safe" upgrade because all you are doing is increasing roll stiffnes.
Most likely you will merely tune the car to "push" more. You then increase
the camber a bit and try to optimize the contact patch. This will dial out
some of the "push" because you are using the tires more efficiently.
However you can only go so far before you start violating basic principles
of physics.
You then move to the rear of the car. Add a rear sway bar appropriate to
the front bar. For example in the above case we may have installed a 7/8"
Addco bar - cheap and effective. To "balance" things, we could install a
3/4" rear bar. Suddenly our "push" will be either neutral or it could even
convert to making the car loose (oversteer). You then "tune" by making the
effective "arm" of the rear bar longer (to soften) or shorter (to stiffen)
the roll resitance.
Still too much roll? Then you play with springs. And so forth.
The idea is to increase one end and then bring that change into "balance"
by playing with the other end.
There are other factors to play with. Suspension deflection due to the
bushing materials can result in camber and toe changes. This is why racers
will toss the stock rubber pieces for harder materials. But there are
tradeoffs. For example stiffer bushings can result in sheer forces beyond
what the mounting points are designed for, so you get cracks in the
frame. That's the tradeoff... better handling - more stress.
You can play with "roll centers" by raising or lowering the car. There's a
reason why most race cars sit fairly close to the ground... the roll
center has been lowered. And most like a lot of other suspension aspect
havebeen changed too, but that's a whole can of worms...
Remember that the designers of the car had to make decisions about
various aspects of the car's handling. We're probably talking about teams
of engineers and "man years" of design, testing and development. Once you
start messing with that, all bets are off and you have to re-duplicate
those efforts. This isn't rocket science, but it's not "takin' out the
garbage simple" either.
You just need to decide what you want to do and then try to dial into that
usage. It sounds rally easy, but you need to apply the scientific method -
hypothisize, impliment, test, analyze, hypothesize...
The situation is further complicated by the fact that the setup for me may
be a whole lot different that the setup for you.
And, of course, when you get rid of roll, you generally get rid of
compliance - it is possible to tune your TR6 into a "buckboard". It'll
corner awsomely, but you feel every pebble that you run over. That's the
nature of the beast.
> TIA,
>
>
>
> Jim Hurley "Life is too short for a backfire!"
> '75 TR6
> '83 F350 4 Door
I hope this helps.
rml
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