There is a tire calculator Here
This will clear up most problems.  Input stock tire size, and new tire size, and it will tell you how far off the spedometer will read in both a percentage and deviation at 60mph.
Have fun, and play around!
-Jeff

i was thinking about this cuz there is something about this up on team-integra.net about this. if you get bigger sizes how would u correct that problem?

apexi rev/speed meter will tell you corrected speed