Change in tire/wheel size & effect on speedo

5.0_GT_kid

20+ Year Stangneter :roc</strong><span class=
Apr 18, 2004
1,155
1
39
Largo, Florida
Sometime this winter I'm buying a set of the 17x8 inch "standard" wheels off a 2004 GT. My car has the "waffle" wheels, which are 16x7 if I'm not mistaken. The 17x8's have the stock rubber on them.

If I were to swap these wheels onto my car, how much would this throw off my speedometer, and what's the simplest and CHEAPEST way to correct it?