I just bought a 2003 Miata. It came with low profile Ventus tires. I have noticed the speedometer is reading about 8-10 mph faster than it should. I believe that this is due to the smaller diameter of the tires. Has anyone found a solution to this problem? I have seen a device called a Yellow Box that corrects the speed, but I can't verify that it will work with the Miata.
Thanks

 

After I fitted white gauges to my NB, my speedo was reading too high, I set it up by removing the clear plastic screen on the instrument panel thenaligning rpm and 70mph with my Sat Nav, Idrove up and down a short stretch of motorway (UK), noting the rpm/speed,leaving the motorway and stopping where suitable, I pulled off the speedoneedle and moved back or forward, rejoined the motorway then checked again, managed to get it spot on after the second attempt.
Hope this helps.Not heard of the yellow box but sounds like it would be quicker than my method, it should work as Miata/MX-5 speedos are now electronic.

 

Douglas[/align]Thanks for the reply. Your solution would fix half of my problem. The speed of the car would be known but my odometer would still be reading more mileage than I would be actually traveling. I found out that the NB speedo is calculated for a 23 13/16" diameter tire. The tire I am using has a 23" diameter. I may persue the Yellow box fix as soon as I can get under the dash and find out weatherI have a 2 or 3 wire speedo cable. The yellow box is supposed to fix the speed and milage error by splicing it in line. [/align]