You've been sent 25 years into the past. To save the world and get back to your current time, you need to design a hidden electric motor inside a bike to change who wins the tour de France. What are the engineering challenges you'd have to overcome to pull this off?

You've been sent 25 years into the past. To save the world and get back to your current time, you need to design a hidden electric motor inside a bike to change who wins the tour de France. What are the engineering challenges you'd have to overcome to pull this off?