KGL said:
I noticed that the BASX wheels are available in two different diameters. In what case would you run the larger or smaller diameter wheels? Is there much weight difference between the two?
TXCHEMIST might be able to back me up on this. The question to be considered on smaller circumference wheel vs. larger is:
1. Smaller wheel rotates more time down the track than larger -- thus -- More friction in bore & axle
2. Anyone who had done any kind of road racing knows that "un-sprung weight" increases speed, thus racers reduce weight in everything that turns (flywheel, pistons, rods, wheels [especially tires & wheels], etc.), at least to the degree they don't lose their strength.
3. When reducing weight on a rotating disk, taking weight off the out edges is more important than taking it out of the inner edges or centers.
There has to be a "diminishing return" the further you go between 1. vs. (2. & 3.) above.
But all in all, #'s 2 and 3 outweigh #1.
This can be proven in many ways manually. E.g. take a tennis sized ball, vs. an iron ball of the exact same outer dimensions and roll then down an inclined plain together. The light ball picks up speed much faster because the heavier ball has to pick up momentum. But if that incline plain is shaped like a pinewood derby track, with a long flat at the end. Depending upon length of the flat, the iron ball, once it has picked up it's momentum, will gradually catch and pass the lighter ball (depending upon the length of the flat part).
You could do the same experiment with a disk. Make two disks that weigh exactly the same of the same material, but one with the heavier part of the disk towards the center, and the other with most of the weight on the outside edges. Roll them down a similar surface, and the result will be the same as above. The one with less weight on the outside is fastest downhill, but the other once it has built up it's momentum, will eventually pass the other on the flat part.
Look at the newer ELIM and UNLIM wheels that are being made by Joel, John, and perhaps others. They take as much weight as possible off the outer edges, and are thicker/heavier towards the center.
But if this is taken to an extreme, the wheel becomes too fragile, and is more prone to getting "Knicks" on the running edges.
So, IMHO, for pinewood wheels, smaller circumference is better.
Now, I am prepared to be criticized by whoever, AND support is also welcome.
