[DeTomaso] RPM - MPH Conversion

[Dan Courtney]

Since "The Beast" does not have a speedometer, I was trying to figure how to calculate my speed off the tach, just to make sure I'm doing at least 95mph at the Silver State so I can for sure get those $2mil US off The Dawg.
The following link calls for rpm, tire diameter (27.2"), and gear ratio (.705, right?). I think I have the wrong gear ratio because it says I'll be doing 49,947,234 miles per hour at 4,000 rpm's.
"The Beast" is damm fast but it ain't quite that fast.
Any mathematicians out there?
http://www.k3pgp.org/uct.htm

Dan