> Wow.
> The "Thomas Walter Tech Post of the week" goes to you, Chris. Cool.
> Now, my feeble attempt to interpret this set of graphs! The roadster
> has some, but not very much, bump steer, and when it does bump steer,
> it toes in. There's little suspension 'give' (it tends to come back up
> the way it went down?)
> Castor changes significantly with suspension travel, but in such a way
> that will save most of our butts, i.e. as you brake and turn, pushing
> the nose down, you get more "push" back from the steering wheel. Our
> springs are linear, but the bump stops are not! Bob Sharp is right once
> again...
> A question: why "Wheel displacement from curb" Is that 'curb height?"
> Again, if I wore a hat, it'd be off to you!
> Toby
Thanks for the kind words, Tony.
Ok, a little more explanation...
On the bump steer plot, positive is toe-in, so the front wheels toe out a
little bit as the wheels travel up. So, when the car steers, and then rolls
into a corner, the front wheel straighten up a bit, which adds a little
understeer. And Toby, you are correct, there is not much bump steer.
The Camber curve is pretty standard for a car with this type of suspension.
As the wheels move up, the rate of change of the camber curve increases, so
the guys with the competition springs will be on an even more favorable part
of the camber curve. The tops of the tires are moving inward as the wheels
move upward. This keeps the tires closer to perpendicular with the road as
the car rolls in a corner. The autocrossers and road racers would probably
like to have a more aggressive camber curve, though.
There is little 'give' in the suspension, which is a direct result of the
metal on metal bushings in our cars. There is more hysteresis than I would
have expected, though. Upon further inspection, I noticed that there was
just a little bit of play in the brand new upper a-arm bushings on the left
side. So the left camber curve has a little more difference travelling up
than it does coming down.
The jounce bumpers are definitely non-linear, but also 'come in' pretty
smoothly.
Curb is curb height. In this case, when the car was set up for the test, it
was empty, and had about 1/4 tank of fuel. Test weight was around 2140 lbs.
So, zero wheel displacement means the suspension is at it's 'curb' ride
height.
enjoy,
--
Chris Coker
69 1600 SPL311-24529
66 1600 G Production Racer
Royal Oak, MI
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