Originally posted by JesseT
Simple diffusers were used in teh 1/12th scale racing a few years back. They increased the rear end traction in fast corners, but didnt' really help with lap times as they introduced pushing in high speed corners, decreased top speeds, more weight and added battery consumption. I haven't seen any for years.
I actually found them quite useful on 10th and 12th pan cars when racing on Asphalt. On asphalt they helped to lock-in the rear, thus reducing tire wear and actually increasing corner speed by keeping the vehicle on line with out an over-abundance of mechanical grip required from the tires. Obviously they'd be of limited benefit on a short, high bite carpet track.
Of course with today's advances in chassis design, they're not really necessary.