My tire truer has four screws that pull down on the pod, and a fulcrum under the motor (the length of HO brass rail). The chassis actually bends at the fulcrum, and behind the motor, because the screws are tight. I tighten the two screws at the tail of the pod about 1/8 turn at a time, to pull the tires down onto the sand paper. For rubber tires, the process goes fast, but for Super Tires sillies
, it takes much longer, and I have to cool the tire with water dripped onto it as I go. Thus, I use wet or dry sandpaper.
I tighten down the rear screws until the tires' high spots just touch the paper. I let it skip along for 10 minutes or so, adding water, then I give it a 1/8 turn down, then about 10 more minutes, etc. until the high spots are all gone and the whole tread is flat. It is tedious and I only bother truing Super Tires for cars that will go into proxy races.
About one in four Super Tires gets discarded around here, due to out of round. The rest are nearly, but not quite concentric out of the box. The best ones are glued to their rims, then sanded to perfection, or as near as I can get.
I typically run the sander at about 4 to 6 volts, with 3.1:1 reduction, and a 19k/12v motor. Sanding (tire) speed is less than 3,000 RPM. I don't think the imbalance caused by set screws is a problem, especially since the axle is held firmly in place.
Direction of rotation is forward, if the motor pod was in a car.
Grit is 220; Norton wet-or-dry from the automotive store. I put a final finish on the tires by running hundreds of laps on the wood track. Incidentally, I believe a rougher grit like 220 provides cooler and faster cutting than a finer grit, as less pressure is needed. The use of 1600 (or any very fine grit) does not seem necessary, as all sanding marks disappear as the tire runs laps. Since the tire does finish itself by running, it is clear that the tire does indeed wear, and does deposit particles of silicone on the track. This would explain the visible, black "groove" laid down by sillies
, and would explain why Ortmann and rubber tires pick up a glaze that destroys their grip.