Which tire grinding machine is the best?

Best? Doesn't exist. There are two different types of grinders, well, let's say three different methods of grinding tires.

The board method

You stick some sandpaper on a rail, give full throttle and slowly push the car's rear axle down onto the sandpaper. Sensible ? No, it's really bad because: None of us have enough feeling in our hands to push the car down parallel enough to produce a reasonable result.

In addition, the engine and transmission of a Carrera car are not designed to work against such high resistance. The service life of the engine and gearbox is therefore drastically shortened.

Tire grinding machine for aluminum rims

There are some suppliers of tire grinding machines that can be used to grind individual aluminum rims. In principle they are all the same and good, but they have the disadvantage that they can only be used to grind one rim and not a complete axle.

Overdrive RSM

The RSM is the only patented tire grinding machine that can be used to grind all rims and axles. No matter whether aluminum or plastic, 1/32 or 1/24. From version 4 onwards, the swivel arm can be adjusted using two grub screws. This is not to grind a cone, but to compensate for manufacturing tolerances.