My Garmin GPS has a MPH and "miles to destination" feature that works very accurately as long as some end point to a trip is programmed. I use it all the time, and rarely look down at the actual speedometer. Tire size, tire wear, and other variables don't affect it.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!