Problem with 1995 Si Speedometer

Since i've gotten 17" wheels with 215/40/17 tires (the "correct" size), my speedo has read 5 mph or so faster than what i'm actually going. Does anyone else have this problem and would it fix it to get a different tire size next time i need new tires? Thanks!

i have 205/40/17's... that's the size you need. right on spec.