Wheel prep, there's a better way!
It is well known for maximum speed the wheels must be properly prepped. This includes sanding and polishing of all contact surfaces.
Surfaces that must be sanded/polished.
The smoother each running surface is, the less friction generated, therefore the faster the wheel will be.
There are currently two options to accomplish this:
Option # 1 – Wheel Mandrel
There are several versions of these on the market, but they all work the same. A threaded thumb screw is inserted into the wheel bore and then tightened into a threaded shaft. The shaft is then inserted into a hand power drill so the wheel can be sanded and polished by holding the abrasive material against the wheel while spinning it.
The wheel mandrels present several problems including:
The threaded thumb screw is sharp and must be inserted (and after polishing removed) through the wheel bore. This makes it highly likely the interior surface of the wheel bore will be scratched by the thumb screw, ruining the bore and killing speed.
If tightened too much the mandrel can stretch the entry to the wheel bore. Larger bores lead to an unstable, and therefore slow, car. The mandrel can also deform the hubs.
If not tightened enough, while sanding/polishing the wheel can start spinning on the threaded thumbscrew leading to significant damage to the wheel bore and hubs.
Because of the way the mandrel grips the wheel it is impossible to use it to polish the outer and inner hubs, nor the bore itself. It is these areas that lead to the greatest increases in speed.
Option # 2 –Pin Gauge
The wheel is placed upon a pin gauge that is slightly larger than the wheel bore. This creates a friction fit. The pin gauge is then inserted into a power drill and spun. The wheel is sanded and polished similarly to the wheel mandrels.
This is the preferred method used by most pro racers, though it still presents some challenges/issues.
The wheel bores of stock wheels can be different sizes. Therefore, a racer must have several different size pin gauges which are expensive to purchase.
The gauge itself needs to be rounded and polished to keep from scratching the wheel bore. This can be difficult due to the hardened steel that pin gauges are made from.
Hardened steel that must be rounded off and polished.
To create the friction fit the pin must be larger than the bore, this can slightly stretch the bore, larger bores lead to unstable Pinewood Derby cars. A purchased wheel that has been cut/trued on a lathe will be placed on and off the pin a minimum of FOUR TIMES before it is ready to race.
If the fit of the pin inside the bore is not tight enough the wheel can start spinning on the pin, damaging and enlarging the bore.
The bore cannot be polished using a pin gauge to hold the wheel.