We use something similar at work to unreel rolls of fibre/cable, try searching for cable roller or reel roller, they are usually rated for weight. personally I'd be expecting the car to roll off when the clutch is let out on the bike, there again I am probably wrong.....again
I have seen an 8 inch angle grinder used instead of those little motors baz
Not sure what "little motors" you are referring to. The starter motors in the pics are Ford auto starters and they definitely are not little. And they really put out the torque. The rollers are kind of violent when the 2 starters engage.
1967 BSA Wasp 1967 BSA Hornet (West Coast Model) 1967 BSA Hornet (East Coast Model) 1968 BSA Firebird Scrambler 1968 BSA Spitfire Mark IV