From there, the Allstar pull bar was pulled in favor of the simpler unit from Coleman Racing Products. This pull bar uses a 1,000-pound spring, and should let the rearend rotate farther than the 1,600-pound Allstar bar. The video confirmed that the lighter-weight spring allowed the rear to rotate almost twice the distance. With the rearend rotating 1.4-inches and about 73/4 degrees, rear steer increased to just under a 1/4-inch.
“I could really feel the reared moving with the Coleman pull bar,” explained Dick. “If I turned a perfect lap, the car felt great, but if I was on and off the throttle, it was a handful. The pull bar has a lot of potential, we just need more time testing with is.”
During each run, we recorded what the pull bars were doing with our ReplayXD cameras. You
Next up was the pull bar from Coleman Racing Products. It is a nonadjustable piece. Its li
The same Penske shock will be used to dampen the rearend movement.
Dick told us the car was tight in the middle and not good going into Turn 3. We found two things causing this. First, the sway bar was loading way too much when the car dropped down on the bumps. This was corrected by backing the bar off two and a half turns. Second, the left front shock had too much rebound. After taking two clicks of rebound out of it, Dick said the car felt much better and drove well through the turns.
At this point we took a good look at the data we had collected thus far. When looking at the video from both pull bars, the pull bar slammed closed as soon as Dick lifted off the gas. The Penske shock installed to dampen the pull bar’s movement did not have enough compression resistence to control the rotation of the rearend. With the movement being so abrupt, it leaves the chassis feeling unsettled, and when you are on and off the throttle, this feeling is amplified.
A stiffer shock will keep the rearend stable while it’s in transition, as it will slow the movement of the rear end. The initial movement of the rear rotating backwards doesn’t need to be slowed, but when you lift off the throttle and the rear slams back into its normal position, it rotates so quickly and abruptly, that it actually bounces and upsets the car. A shock that has stronger compression, equal to the spring rate, will slow this movement, calming the rearend to settle back to its normal position easier.
Over the course of both test days, Bob Bolles took exact notes and everything that happene
Something else that needs to be addressed with any of these pull bars is proper driveline geometry. Whenever the rearend rotates, the pinion angle changes. In our case, an inch and a half of rearend rotation equals 7 degrees of pinion angle. The static driveline angles need to be set with rearend rotation in mind. This is to be sure that under acceleration there are equal and opposite angles. We also found that a shorter third link would give us the pinion angle we need with the rearend rotating. In the future, we are also going to try a 1,400-pound pull bar spring, as an inch and half is probably more movement than we need.
Our test took place over two days, which were almost a month apart. Because of this, we haven’t really talked about lap times and time gains on track. But without seeing gains on the stopwatch, we saw gains on the stopwatch (this doesn’t necessarily make sense, but I’ll explain). When we made the change from the solid third link to the Allstar pull bar, we went 2 tenths quicker right away. We also made some setup changes as each test went on. But over the course of each test, which consisted of about 75 laps, our lap times were consistent and never fell off. The first test was on a set of old tires and the second test was on a set of new tires. Each test ended with lap times on par with our early lap times. Looking at this data, we strongly feel you would see a solid 3 or 4 tenth gain if each set of laps were done on equal tires. The other benefit we found is that this setup should lend itself well to long races, as the car remains very drivable over long on-track periods.
Be sure to go to www.circletrack.com to check out the ReplayXD video from our tests! And feel free to email us with your questions, comments, or experiences.
Desoto Super Speedway