TIP
You can set up your car to "autopilot..."
When you have your races with humans, and need races in zone, assuming your car's basic numbers are = or greater than the challenge numbers, take out the boosters & shields, anything you have to click for, load up the spikes, etc, and you can start and finish a race with CPU or human without having to click the meter... so you can multitask.
Just take out stuff you have to click the challenge meter for... turbo's etc... start the race, check back later, it's done, race again. You may get less points per win, but it isn't boring if you are reading an email while the car races.
When I feel like really racing, I put the other stuff back on... when I am just meeting requirements( x wins, x races in zone) it is helpful to have autopilot...
Lol thats what I do! And, if you buy a new car in your class, even if you have nothing with which to click, you will pass every challenge