Sorry, I don't have any advice on how to get out of it--I've had to pay almost all of mine. But I would give you a word of warning. It's not likely a wheel and tire change would mess your speedometer up that badly. So if it was really reading 75, I'd borrow a GPS unit and try to get a feel for how bad it's off--there's something else wrong with it. Or you can do the simple method--watch your odometer between mile markers. If your odometer reads .81 miles instead of 1.0, your speedometer is actually off that far, so watch yourself.
08 700XX (Gray, L8ton Racing Stealth Bumper, 13 tooth, 21" Razr2 fronts, stock rears, Precision Pro stabilizer, Fox Evols and Podium Xs, Teixeira Tech stock-length upper A-arms, Teixeira Tech stem, L8ton Racing 9/16ths sway bar, ProTaper Contour bar, Shock & Vibe clamps, EHS lid & programmer, HID headlights)
08 Outlander 800
08 Yamaha Big Bear 400 4x4