Version 2
The rest of the arm/leg joints are enabled with varying speeds to allow for greater speed control. Also, the chest turns more slowly.

There are four joints controlling each wheel. This allows for 2^4 - 1, (2 to the 4th power minus 1) or 15, possible speeds. (this excludes stopped)

If you understand binary, this should be easier to understand.

The innermost joint (pec/glute) is velocity 4.
The second joint (shoulder/hip) is velocity 8.
The third joint (elbow/knee) is velocity 16.
The outermost joint (wrist/ankle) is velocity 32.

The slowest speed other than stopped (hold all) or neutral (relax wrists/ankles, hold everything else) is moving just the innermost joint, and holding everything else. (velocity 4) You can express this with binary - 0001.

To go four velocity units, or one speed, faster, use just the second joint. (velocity In binary, this would be 0010.

For velocity 12, use the two innermost joints. (4 + 8 = 12) 0011.

And so on:
Third joint / 16 / 0100.
Third and innermost joints / 16 + 4 = 20 / 0101.
Third and second / 16 + 8 = 24 / 0110.
Third, second, and innermost / 16 + 8 + 4 = 28 / 0111.
Outermost / 32 / 1000.
Outermost and innermost / 32 + 4 = 36 / 1001.
Outermost and second / 32 + 8 = 40 / 1010.
Outermost, second, and innermost / 32 + 8 + 4 = 44 / 1011.
Outermost and third / 32 + 16 = 48 / 1100.
Outermost, third, and innermost / 32 + 16 + 4 = 52 / 1101.
Outermost, third, and second / 32 + 16 + 8 = 56 / 1110.
All / 32 + 16 + 8 + 4 = 60 / 1111.

Though if you want to be mathematically correct, you'll have to use ternary, because you can hold, contract, or extend joints. But you probably don't care.

There are two files attached: cars2_race.tbm is side-by-side (note that Uke is very slightly forward) and cars2_fight.tbm is facing each other, like the original.

Version 1
Turns the characters into living cars.

Most of the joints are set to zero range, so they're basically stiff.

The wrists and ankles (hidden by the hands and feet, respectively) control the wheels. (the hands and feet) Unfortunately, there's basically top speed and zero, and not much in between.

The chest turns the front wheels. (turning is, of course, easier when the wrists/ankles are set to relax) Of course, real cars' wheels turn quite a bit differently... but this is simpler and works about as well.

Physics are decent: It should work fine, but can be a bit of a pain. Okay, the physics are pathetic. At least, that's what someone else would say. I'd say they're more fun.