Roll Stiffness of 1988 Carrera

[burgermeister]

Probably the last thing I'll measure on my car.

Around 1480 N*m/deg as directly measured.
Obviously the actual car does not apply all of the roll moment in one spot. Also, calculating roll stiffness from spring rates et al usually assumes a rigid chassis. Given a chassis torsional stiffness of 5500 N*m/deg, one can correct this to a "rigid chassis" roll stiffness of 1580 N*m/deg.

This works out to a roll gradient of 3.9 deg/g with 400# of passengers, and 3.1 deg/g for an empty car (which is surprisingly difficult to drive...and therefore possibly a pointless number). Assumptions are a car CG height of 480mm, cargo CG height of 800 mm, edit: forgot RCH 100mm.

This further works out to a "loss of negative camber" of 2.3 - ish degrees, front and back. FWIW. Which ain't much ...

Pictures ought to be mostly self-explanatory. The brute force method involves a digital angle finder and me balancing my weight on a 2x4 strapped to the chassis using the jack ports. Due to the resolution and accuracy of the angle finder (0.1 deg) it is necessarily coarse. The long arm method uses 2 dial indicators placed under the rear jack pads (not ports) to measure roll angle, and the usual bathroom scale. I got a fair bit of tilt into the car ...

A picture a buddy took of my car in a flat, steady state, steering just about washed out kind of curve (I'll guess at 0.8g lateral on street tires; it's the paddock curve at Waterford Hills) suggests the numbers are at least ballpark correct.

[911st]

Burg, I love you mind!

So, you are saying a stock Carrera in a full on turn leans about 3 deg. I have been looking for that info for some time.

Other variables are car height (position of roll center and CG) , tires ( .9 v 1 G turn), and air pressure. Did you set the tire air pressure at the hot air pressure we usually run our tires at on the track?

About how much camber gain are we getting in the front and rear suspention because of there design on a euro height car?

How much of the lean is from springs and how much from the tires? If it is half each and we double the spring rate, we will only reduce the lean 25%.

I have been running with stock springs and street class race tires with about -3 camber in the back and -1.25 in the front so I am using up all the static camber with the lean and then some in the front.

Getting enough neg camber to make all the tire work looks will require stiffer springs and some major work on the front to get the camber we need to make the tires work to there potential.

I suspect many of us are not using all the tire we have.

[Flieger]

Good work, burgermeister

[ShakinJoe]

nice!!