Double rollers on a Super-II: why 13 and 12 mm in one piece

Two rollers in one piece. The bottom one runs the fence; the top one saves the car when it leans.

Tamiya machines 15398 as one aluminium piece: a 13 mm roller with a 12 mm roller above it. Normally the 13 mm touches the fence. When the car tilts in a corner, the 12 mm touches instead and stops the car rolling over. Four 520 bearings come in the set.

15398Double Aluminium Rollers (13-12mm)Part page ›

This is the standard front setup in the book. Racers also run the smaller 9-8 mm version, which Tamiya says weighs under half as much, or lighter and cheaper plastic doubles.

The variations

• 13-12 mm aluminium double, 15398: the one on this car. ¥1,210.
• 9-8 mm double, 15403: smaller, under half the weight.
• Plastic double 13-12, 15457: low friction, cheapest.
• Rubber-ring double, 15418: more bite on the fence.

Under the double on each front corner sits 15437, a ringless 13 mm aluminium roller with a bearing, only 2.5 mm thick. Three parts on one screw: the double, the plain 13 mm below it, and a tube stabiliser on top.

1543713mm Aluminum Ball-Race Rollers (Ringless)Part page ›

The B-MAX ruling

Rollers count toward the car's width and must stay outside the zone between the axles. A double roller is one roller for the count. The limit on the number of rollers and the width rule are in the book, with the drawing of a front corner stacked part by part.

This is one page of the book. It goes part by part through the whole car: the plates, the rollers, the brakes, the wheels and tyres, the shafts, the hardware, each with its drawing, its item number, its price and the rule it answers to.