My Diaries

A Lurid Tale of Obsession, Depravity, Wits and Attempted Wit

Mon Jul 5, 1999

Insight, maybe, into Gran Turismo severe bouncing problem

1) Balance Springs and Dampers

Last night I was tuning up a Griffith 500 (no race-mod).

At one point it got the "Demio dance" phenomenon, where a slight bump lifts the inside wheels way off the ground, and it reverberates a couple of times. Previously, I have fixed this by softening the dampers. Now, that does work, but it makes the car sort of "wobbly", and now I'm getting better at the "Hard-Tuned Car Speed Contest" (which I call the "Abnormal Series", for short), I'm getting more demanding about the handling of my cars.

So I tried something else. I put the dampers back to their default setting (4), and *raised* the spring rate all round. Just two notches (.2). And the phenomenon went almost totally away.

All I can figure is that GT sort of counts "dampers" as a force to cancel out the rebound of a spring, but, especially with light cars, allows excess damping to generate a force which severely lifts the inside wheels. This is partly as a consequence of deliberately exaggerating effects to provide visible feedback.

Anyway, the upshot is that balancing springs and dampers seems more important than one would expect, and that, while the lifting off the road does seem reasonable as a visual exaggeration of the effect of overly-stiff suspension, the suspension isn't necessarily overly stiff, but may be just overly damped for the spring force being used. *And* (restating again) that problem can be fixed by either increasing the spring force, or reducing the dampers, with different side-effects for each solution. Further more, you can "stiffen up" suspension, but still control bounce if you keep the dampers properly balanced with the springs.

(One should also note how slight the spring rate change was, and what a big difference it made). This was with stabilizers no less than 3/3, and perhaps 4/4 or 5F/4R (though the TVR's have fairly natural understeer, unless provoked by brake or throttle).

I should experiment with very high spring rates and low dampers, to see what that looks like. I would not be surprised if a similar (but slightly different) oscillating bouncing set in in that state, too. In which case, you need to guess which way out of balance your springs and dampers are in order to be able to adjust one or the other appropriately.

2) Different Stabilizers Easy Way to Setup for Different Course

As far as stabilizers go, I am finding that it helps a lot at Autumn Ring ii to use 3/3 stabilizers on cars where I usually use more on most tracks. The speed is slower there, so oscillations under braking and cornering are easier to control, and the lower stabilizers lets you drive around the corners rather than sliding. The body roll is even useful for judging your cornering limits, and, when the body rolls without the tires, the inside tires keep more cornering force. (Until such a time that the weight transfer is significant enough to start secondary effects).

With real light-weight cars such as Demios, Glanzas and Civics, I tend to run with no stabilizers; the tracks in the FF and Lwt series tend to suit agile rather than stable setups, and the 0 stabilizer setting seems to keep all four wheels on the ground, too. Probably, springs, stabilizers and dampers all need to be balanced, although you seem on most cars to be able to get away with tweaking just stabilizers to get desired effect without too many side-effects. Well, I guess I imply that's true except for those very lightweight FF cars.