LIMITING RF REBOUND TRAVEL TO EQUALIZE REAR TIRE LOADING ON LAUNCH

This is a little trick for both oval and drag cars. First, oval cars: You most likely already have chains which limit rebound travel of the front suspension. To gain extra traction during restarts, I'm simply suggesting that you shorten the right side chain a bit. Since the shorter chain will be on the outside wheel, it will remain slack in the corners. And, drag cars: To reduce 60 foot times and gain directional stability, I'm suggesting that you limit...with a chain...the drop (rebound) of the right front wheel ONLY. Now, as to the reasoning behind this: Observation of the front of the car, during forward acceleration, reveals what is happening at the rear. With non IRS cars, a premature lifting of the left front tire will be seen. As discussed in detail elsewhere on this site, this is the effect of driveshaft torque. With a drag car (or, with an oval car during a restart on the straight), the sum of the wheel loads...on each side...remains constant. So, if the LF is losing load quicker than the RF, that means the LR is gaining load quicker than the RR. In other words, you don't have equal loading of the rear tires and, consequently, maximum acceleration is not achieved. On Page 16 of this site, I explain how a RF spring rate greater than the LF can dynamically cancel the effects of driveshaft torque and provide equal rear tire loading on launch. When the chain at the RF goes taut, the effect will be to have a spring of infinite rate. While this is not as "neat" as a dynamic cancellation with different spring rates, it does provide a means of equalizing rear tire loads. Instead of the rear tire loads remaining equal for all values of driveshaft torque (dynamic cancellation), they will be equal only at a value which corresponds to the car's maximum acceleration. Realize, however, they will be very close to equal for a range of driveshaft torque values; much closer than they would have been without the chain. THE PROCEDURE: First, use Pages 9 & 11 to determine the weight transfer. At this point, I'll introduce some numbers, hoping that it will clarify the procedure. Let's assume total weight transfer to be 1000 pounds and that the static LR load is 875 pounds and the static RR load is 725 pounds. Next, hook up the car to a traction dyno and tension the chain. I'll complicate matters slightly here and say that, though the CG height is known to be at 18 inches, the only convenient place to attach the chain was at a 12 inch height. With the traction dyno chain tensioned, the LF scale reading is reduced by 267 pounds and the RF scale reading is reduced by 133 pounds. Multiplying these readings by the ratio of 18 to 12, we see that the actual weight transfer, for this particular chain tension, would be 400 pounds on the left side and 200 pounds on the right side. If the rear tires are to be equally loaded with 1000 pounds of weight transfer, 425 pounds must be added to the LR and 575 pounds to the RR, at which time LR = RR = 1300 pounds. But, when 425 pounds transfer on the left side, only half that much (ratio of 200 pounds to 400 pounds) transfer on the right side. So, remove the traction dyno chain, place a jack under the front of the car, and raise it until 425/2 = 212.5 pounds are removed from the RF. Install the RF rebound limiting chain so that it is taut under these conditions. As the driveshaft torque value is increased from zero, the chain goes taut as the LR load hits 1300 pounds. The LR load will remain at essentially that level while the chain transmits the remainder of the weight transfer to the RR, with both tires at the 1300 pound level at maximum acceleration. Obviusly, a rigorous application of this procedure would require iteration, since improved traction would increase maximum acceleration, which would increase weight transfer. It is doubtful, however, that a single iteration would produce measureable incremental results. It is recognized that loading transients would occur as the chain goes taut, but the time involved would be small compared to even the 60 foot time.