By Randy Davis
Several times I have had people tell me that their car did great in preliminary events, but then in the finals the car lost speed. They asked me why that happened. I then offer several possible reasons:
– Loss of lube (response: “It didn’t run very many times.”),
– Car damaged (response: “Didn’t see any mishandling.”),
– Different track (response: “No – same track.”),
– Temperature change (response: “No – climate controlled room.”),
– Different person staging (response: “Uh – yes, I believe a different person staged the cars.”).
I can’t say for certain that staging accounted for the lower speed, but it is certainly a possibility.
But how much does staging affect car performance? Certainly it has to have some effect, but is the amount of the effect really measurable? Let’s find out.
Six staging variations were tested:
Figure 1 – Car Staging Variations
– Straight, centered, wheels pulled out to axle heads.
– Straight, centered, wheels pushed in to car body.
– Car shifted left as far as possible, wheels pulled out.
– Car shifted right as far as possible, wheels pulled out.
– Car angled, pointing to the left, wheels pulled out.
– Car angled, pointing to the right, wheels pulled out.
The car from “Shifting the Wheelbase” in V14, I11 was reused.
The car is equipped with Pro-Stock Speed Wheels and Polished BSA Speed Axles. These wheels and axles were cleaned, and then the car was re-lubed with Krytox 100.
On this car, the front-left wheel was raised, and the front right axle was bent for aligning. The car was set to rail-ride, by drifting left five inches over eight feet.
Figure 2 – Test Car
Each staging variation was tested once, and then the cycle was repeated five times for a total of 30 heats.
Wheels Out – 2.549
*Wheels In – 2.547
*Shift Left – 2.547
Shift Right – 2.551
*Angle Left – 2.547
Angle Right – 2.556
The results were a bit surprising. I expected more variation, but to my astonishment the three starred results were the same, while the “Wheels Out” number was very close (this could just be statistical noise as the standard deviation was just over 2ms).
Clearly, the worst performance was attained when the car was shifted or angled right. This can be readily explained due to the raised wheel contacting the guide rail at the start. This contact would result in some energy loss, and thus reduce performance.
So, what we can draw from these results is that with a raised wheel, make sure that the raised wheel is not in contact with the guide rail at the starting line. This clearly is detrimental to performance. But otherwise, you don’t need to get too fanatical about perfect staging.
Now, I guess I’ll have to come up with some other reasons for slow performance in the finals.
From Pinewood Derby Times Volume 15, Issue 2
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Maximum Velocity Pinewood Derby Car Plans and Supplies
By Randy Davis