Page 36
TRACTION DYNO TESTING
ON A GRADE

On page 4, I describe the concept of a "traction dyno." On Page 5, there are further comments. And, on Page 6, there is a spreadsheet for use with the traction dyno. Many cars, however, have no convenient location point for the tether. It has occurred to me that...instead of applying a force through a tether...gravity can be used to obtain the same information. Apart from the wheel scales, the following procedure requires only the availability of a convenient grade upon which the car can be parked. The procedure will not, of course, simulate the loads experienced during a maximum acceleration launch, but, since it is quite reasonable to assume linearity, the data can be extrapolated with reasonable accuracy. Still, to maximize accuracy, the grade chosen should be as large as conveniently available. The default numbers in the spreadsheet are based on a 10% grade, which should be easily found. Driveway entrances are often much steeper.

After scaling the car, park it...nose up...on the grade. Place the transmission in reverse (or "Park" with an automatic) to hold it on the grade. DO NOT ENGAGE THE PARKING BRAKE! Then, place wheel scales UNDER THE FRONT WHEELS ONLY and note and record the readings.As with the initial scaling, the car should contain the normal driver and fluids. (It is advised that either the parking brake be engaged or chocks placed behind the rear wheels as the car is jacked up for placement of the scales. Be certain, however, that the parking brake is disengaged or that the chocks are not contacting the rear tires as the scales are read.)

That completes the procedure. In addition to the wheel scale readings, other parameters unique to your car are required in the spreadsheet. Be certain to input the proper values for your car, as I have deliberately used some "crazy" values in the sample calculation.

The warning indicates that the 60 foot time input has resulted in an acceleration that, in turn, caused one or more of the front tires to lose contact with the strip surface. I'm not saying this shouldn't happen, but it's simply impossible to calculate rear wheel loads when both front tires are not in contact with the strip surface. It will be necessary to increase the 60 foot time input sufficiently to eliminate the warning.

This spreadsheet is intended to facilitate the test process. Since the scale readings are interrelated, it cannot be used for "bench racing."

ANSWERS:

Launch Loads:

Acceleration in g's

Left Rear

Right Rear

WARNING: