Well I guess I can do a speech on Road Biking only. I need 3 main points for the speech.
1. The bike/Gear - tights, shirts w/ water bottle holders, bike it's self, emergency flat tire stuff
2. The benefits - exercise, scenery, comradery
3. The dangers - prostate, cars, crashing, dogs.

How would that work? I'll bring my bike in too to show the class. If I had more time I'd show them how to change a tire with a CO2 cartridge.