Wouldn't that through off the speedometer and odometer reading?

 

because the 16" tires use a lower profile (55 series) giving it a slightly shorter sidewall height.

 

I went from my stock 15" steel rims to my 16" MB Motoring (winter rims) and my 16" chrome rims and i dont have any problems with it throwing off my speedo. It will all depend on your final wheel height. On the stock 15" rims w/ 195/65/15 have the same height (really close) w/ a 16" rims w/ 225(or even 205 or 215)/55/16. With the 225/50/16 is a bit smaller in height vs the stock tire/rim setup.