Speedo vs. MFA WRT Tire Size

[Jeff Newton <Jeff_Newton@pmc-sierra.com>]

Howdy all,

I am aware that our speedos are optomistic but the MFA is quite
accurate.  Can someone explain to how this happens?  

My curiousity stems from the fact that I am contemplating going with
a 215/45R15 tire that has a radius of 287.25mm.  Stock is 282.75mm.
I know the speedo will be higher by an additional 1.4mph but what
about the MFA or overall milage (not gas milage but total miles
driven)?  

Cheers,   

----
Jeff Newton