Get rid of the technological race for faster easier-to-ride bikes and put them on BMX's, no gears.
This sorts the men from the boys when it comes to hills, of course going downhill they can perform tricks to save the crowd from dying to death from boredom.

Only one Grifter style mudflap allowed to be added after each circuit, to enable the motorbike sounds.

Ask them all politely to not use drugs.

We're all responsible adults here, no need for draconian piss testing, just look in their eyes to see if they're telling the truth.

Either that or go the whole hog and use nano-enhancements, fuck it use motorbikes and call it speedway.
Boredom averted.

No need to thank me.