I would have thought the out runner motor would have High Torque because of the multiple coil energising coupled with the effectively large rotor diameter.
That being said the rotor mass is also quite large albeit rotating at a far lower speed that your typical 540 rotor. Wonder if gyroscope type forces come in to play? Could be a stabilising force helping keeping the wheels pinned to the track.
Crude check could be spin up the motor on the axle set up and try to rotate the chassis (hand held) at 90 degrees to the axle line, you could feel any torsion/twisting effect if its significant.
Just food for thought
