ganz

With all the modifications involving the suspension and tires, I am curious to know if there is a way for the average Z owner to make a quantitative measurement of the improvement these products have over stock.

Have any members here had experience measuring Gs on the skidpad? Suppose I wanted to make a measurement after a coilover and sway upgrade -- who would I go to?

On that note, what would one need to do to get the car close to or over 1.0g while keeping body roll to a minimum?

Sorry for all the questions... I'm really interested in improving the handling characteristics of the Z but my ignorance is killing me Any info/advice is much appreciated.

Mr B

iTrader: (2)

Just borrow my Gtech when you come back. It's free for you and you can kinda see what kinda G's you get. Plus you can practice your 0-60 and quarter mile. It's not like perfectly accurate, but you get the general idea.

nwind21

Lower car.
Anti-sway bars.
Suspension.
Wider track (i.e new wheels, different offsets).

I've heard the home mechanic way to heuristically improve/tune your suspension is to find an big empty parking lot, draw a big ring... and start doing circles till you lose traction and have a record when you begin to lose traction + the various specifics of your suspension tuning per run. Bring a temp gauge to measure your temperature on your tires too cause that can tell a lot. Also having a observer recording the performance (video tape, etc) can give some good visual clues on how the car is performing.

I also learned recently that increased positive offset from stock for most cars will make a car harder to steer since it throws off the steering. So it's usually best to increase the track on the rear, but not too much from the front. Then once you increase your track, your suspension adjustments should be changed to adjust for any side effects from the added track.

Also any suspension tuning should be done with weight simulating a driver and/or passenger.

Just some thoughts and suspension theories. Eventually I'll get a chance to try them out, but got no cash to experiment with.

Oh yeah, the ring you're suppose to drive around I think is specific... I'll go look it up when I get home.

DarkTalon

I know the G's measure is a calculated quantity that relates the time it takes to complete a circle.

You draw a circle (200 ft is pretty standard) and measure the time it takes you to go around that circle.

Sorry, I don't know the exact formula but you can now search for that one yourself.

julian

Not sure if this is right in application but angular accel = velocity^2 / radius. You know the radius and the distance/time for average velocity... just not sure if you use the inner or center of car radius.

1g will be very difficult to achieve. Fat sticky tires and a lower CG are a must, but your CG is limited by design.

The portable accelerometer is easier and more fun to experiment with.

Desmo

Most numbers you see in a magazine are an average of one run in each direction around the skidpad. In other words, an average of how well the car sticks turning left AND right. Most cars will be better in one direction or the other because of a biased weight distribution (from the driver's weight if nothing else).

Also, the best numbers usually come from the first or maybe second lap around the pad. After that the tires start heating up and traction goes away. A good testing driver is able to take the car immediately up to the limit, hold it there for a complete lap, and then be done. Note that if you are monitoring tire temperatures and making adjustments, you should probably do at least five laps to make sure they have reached some type of equilibrium, but if you are making those sorts of adjustments you probably know all this stuff already.

The skid pad g-force number comes from the following equation:

g-force = 1.227 x (radius / time^2)

where radius is in feet and time is in seconds

A typical skid pad is 200 or 300 feet in diameter (remember to take half of that for the radius measurement in the equation). I think the size of the skidpad does have an effect on the results so make sure to keep that constant when comparing numbers. Also, the radius would be from the circle that the middle of your car passes through, or more technically the circle that the center of gravity of your car passes through (which is near the centerline of the car).

I'm not sure how much I trust the g-Tech testers in skid pad tests because the body roll of your car will have an effect on the result. As the car leans away from the corner, the accelerometer in the g-Tech will lean and will experience a gravitational pull in addition to the centripetal pull that come from cornering. That will give you a higher g-force number than actual. So if you put on stiffer swaybars to reduce body roll, you would see a smaller improvement in your g-force number than you perhaps expected (assuming the sway bars did in fact add to your skid pad rating). The new g-Tech Pros should fix that because they use three axis accelerometers instead of one, plus it looks alot cooler. (Anyone have one yet and willing to post their thoughts in a new thread?)

Also remember that the track surface will have a large impact on your testing. A greasy K-Mart asphalt parking lot may not be the best place to try and reach the magic 1-g number.

Lastly, remember that cornering in a steady state like on a skidpad is only half the story. Transitional turns, like a slalom, are an equally important part of changing direction, especially if you are autocrossing.

Desmo

ganz

Very informative, Desmo. Thank you! I'm not sure I have all the right tools to test this, but it is baffling to me that with so many auto enthusiasts around, we don't see very many skidpad testing facilities unlike dyno facilities.

I will definitely look into this G-Tech tool though. If I ever get around to actually testing skidpad I will try to post up a good testing solution for us all.

Perhaps one day we can get some knowledgable folks together and have a skidpad day

ganz