Leadfoot is one of the Autobots' premier infiltrators. He has no problems staying in his vehicle mode for extended periods of time, just waiting for the perfect opportunity to strike hard, fast, and final. With his incredible speed, he'll be gone before the Decepticons even know he was there - and when he combines with his Mini-Con partner Pinpoint, they can't even see him.
Need an example of how stealthy Leadfoot is? His "disguises" can only be found on certain Earth race tracks, and he still doesn't raise any suspicion.