On Sun, 22 Dec 2002, Jim Swarthout wrote:
> To the list,
Hi Jim.
> What happens to your TR-6 when you "put it" into a corner?
With the stock alignment specs, the car will understeer or "push" into the
corner.
If you upgrade the suspension, you can reduce the amount of push a lot,
but I will warn the would be Marios (or Stirlings. if you please) that the
crossover to a more neutral car will almost feel unnatural to most
drivers, and this is particularly true with race tires (for example "DOT
legal racing tires like Hoosier A3SO3's or the Kumho V700's).
When I switched to real racing tires for the street car (I used to run
SCCA Street Prepared), the amount of tire slip angle needed to change
motion was AMAZING. I actually spun the car out two or three times on my
first run! Once I learned to induce less steering input, the car was
easier to control - but it takes _very little steering input with the race
rubber_.
When you decide to put a rear bar on the car, you need to be very careful
driving in the wet, it's really easy to get the back to step out with the
rear bar and a moderate amount of stiffening in the shocks (e.g. Spax set
to the top three or four most firm settings).
> What happens
> at the threshold when the tires begin to slide? Does it over-steer,
> under-steer, or is it neutral...how do "you" know how to set-up your
> suspension?
Well, I've tuned my cars to be more neutral in the dry, but the cars are
almost diabolical in the wet! You can't relax in the wet with my setups!
Notice I say _almost_ diabolical. The cars are predictable, but I don't
get enough seat time to know exacly in every situation how the cars will
react, so on the street, I always try to leave two or three "margins of
error" just in case.
Truth be told, it is worth it to get a ride in a car that is setup
properly so you can observe what you car is capable of. I love taking
students out in their own cars and showing them the limits, most folks get
out of the car very "wide eyed". Then I like to put them in my car and
show them an even higher "limit".
But to answer the second set of questions, my street car (lowering springs
with increased rates (425/525), Addco 7/8" front and Addco 3/4" rear, with
Spax adjustables on the front and re-valved Armstrongs on the back) will
tend to initially push, but if you feather the throttle you can get the
car to rotate almost to oversteer and you can hold almost neutral steering
through corners with the occasional oppostite-lock input if the car
over-rotates.
Note: you can tune out a lot of the push on a stock car just by playing
with the alignment. For example, just adding a bit more toe "out" in the
rear can make the car really tail-happy, but you need to know that there
is signifcant dynamic toe change in the rear of a TR6 (or any
semi-trailing arm suspension) so you can effect toe change by applying or
lifting from the throttle. Adding negative camber in the front also helps
the car hold corners better.
The race car is using bias tires, so it runs higher slip angles, but the
effect is almost the same as the street car except that I can toss the
race car into a corner at 75 MPH and _know_ it'll stick. The street car is
a more a _hope_ it'll stick. The street car sees some sideways time in the
wet.
I guess the more important question is "what is the purpose of your
question"?
Mike M. is right - you can write books about this stuff.
> Jim Swarthout
regards,
rml
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