In a car you're fairly insulated from noise and traffic. On a motorcycle, your dealing with a lot more for example balance, keeping track of other motorcycles, cars, trucks, obstacles in the road like potholes, and also weather. Your eyes are constantly scanning and the head is turning a lot.

So in that respect, your brain and body are working harder to process everything that's going on. Couple that with a sunny day and you can be dealing with other stresses like dehydration.

Stimulants like coffee have helped me deal with all of the different inputs which I'd argue are more on a motorcycle than that of a car.