See Page 37 for another...possibly more convenient...form of the traction dyno. (The procedure on Page 36 can also be used, but I would recommend the Page 37 procedure, as it allows all work to be done in the shop.)
On page 4, I describe the concept of a "traction dyno." On Page 5, there are further comments. I realize, however, that
the actual use of the traction dyno can expose some complications which might not be immediately apparent from a reading of
these two pages.
The complications disappear if the car has equal LR and RR corner weights, the chain can be connected at the CG height,
and the rear axle assembly weight is negligible when compared to the total weight. But, of course, these conditions are not
common. You might be using some static preload, so LR and RR weights might be quite different. It might not be convenient
to attach a horizontal chain at the CG height. And, with many cars, the rear axle assembly weight is a relatively large part
of the total weight.
The following spreadsheet allows the user to input these deviations from the "ideal" and yields the actual rear wheel loads
Be certain to input the proper values for your car, as I have deliberately used some "crazy" values in the sample calculation.
A warning has been added (02/23/2009)to indicate 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.