Skid Pad Testing

This is my first post here and let me say that I love this mag and read all the tech stuff vary carefully and keep a lot of issues for reference.

I was reviewing the "Street Fighter" article from the Oct 2007 issue and have a question. The article makes a bunch of changes to a Miata and looks for results on the skid pad. Some changes produce better than others, but nothing stands out as the main item. Then they go to the AX course and make some more mods and nothing produces any miracles. Then they toe-out the front end to .250" total, and whamo everything is great! The toe-out helps attack the slalom better because it helps the transitions. But then they go back to the skid pad and total time is reduced by over 1 second!!! What gives? How did changing the toe-out increase cornering capacity by that much? This question was never addressed. Please, someone help me understand this.

Thanks, Bill C

I would say that it was the transitioning (right to left, or left to right). The skid pad only test steady state cornering which is only really analogous to a very long sweeping turn (or a freeway on / off ramp).

EDIT: Opps, sorry I read that too quick.

I agree 100%. That's why I don't understand why the additional toe-out caused such a dramatic improvement on the skid pad.

Will someone please explain this!

In a turn, the inside wheel is traveling a smaller arc than the outside wheel. Therefore, a little toe out usually makes the car more eager to turn because the tires aren't fighting each other. The enginerds on here can probably explain it more thoroughly than I.

i think in that caseit may be as josh implied, the effect of toe out simulation akermann geometery and reducing the drag imparted on the front suspension.

Toe out sure isn't fun on a daily driver Miata, though. Dart-dart-dart. Exhausting.

josh got it right, and here's some enginerding for you:

just as there's an adhesion versus rotational slip curve in braking, so too is there an adhesion versus angular slip in turning. changing the toe by that amount, on that car, on that diameter skidpad, moved the one or more of the front tires closer to their peaks, such that the sum of front adhesion increased.

practical observation of this phenomenon: when you're pushing through a turn, does it help to add steer angle? NO. why not? because your front tires are already past the peak of the adhesion versus angular slip curve, and more angular slip actually results in less adhesion. how do we get the front end to grip again? two ways: lift slightly, to move some weight forward; and take out some steering, to get the tires back closer to the peak of the curve.

Thanks for all the responses, quite educational! I am just really surprised that after playing with camber and air pressure and sway bars and all that, the one thing that made the biggest gains was front toe! I've gotta get to work and start developing my 914!!

Thanks guys.

dculberson wrote: Toe out sure isn't fun on a daily driver Miata, though. Dart-dart-dart. Exhausting.

From a practical standpoint, this is worth remembering; a car that "wanders" is no fun for a DD.

NYG95GA wrote:

dculberson wrote: Toe out sure isn't fun on a daily driver Miata, though. Dart-dart-dart. Exhausting.

From a practical standpoint, this is worth remembering; a car that "wanders" is no fun for a DD.

I drive wandering cars, almost daily, but I do remember the days when one of my cars did not dart on interstate ruts. It is not too bad but you have to pay attention to the surface of the road.