I have 16 inch rims on my car(came that way) and I am using 205/55r16 tires.
using the tire calculator on Miata.net, it shows that my speedo should be 1.4 mph fast @ 60mph (actual speed would be 58.6) comparing stock size of 205/65r15. However, my speedometer is about 5-6 high @ 60-70. I have swapped in a VE gauge cluster, but the problem existed before the swap (hoped the inconsistency was due to the speedo). so I am trying to figure out what else I should check before I consider a new set of wider tires (215/60 shows it being 1.6 off the other way @ 60).
any suggestions?

 

it could be the speedo sensor gear , but I doubt it.