Wheels and Speedometers

[Kevin B]

I've been reading about people's wheel upgrades to larger diameter sizes. Has anyhone had to get their speedometer recalibrated after making a wheel swap? A change in diamter can throw off the speedometer. I'm wondering how far you can go without affecting the reading?

[Mean Green]

On these cars you can not get your speedo recalibrated. This site will tell you the difference in speed
http://www.miata.net/garage/tirecalc.html
On my GT when I went from factory 205/50-17 to 205/40-17 my speedo is now 6.4% too fast. At 60 mph I am actually doing 56.1 mph. I just compensate with a 4 mph difference. You can adjust going to a bigger size tire by going to a lower profile tire if you want, in other words if I went to a 205/40-18 I would only be reading 2.4% too fast and going 58.5 mph instead of 60 mph. You can play with the numbers and see what you want.

[CREWZIN]

I went from the OEM size 205-55-16 to a larger 205-50-17. My speedometer is reading .08% too slow so when it reads 60 mph I'm actually doing 60.5 mph. Not enough to worry about.

[Kevin B]

Your reports are good news. I'm still thinking of going with the full moon disks from Speedway Motors. If I did I would like to put a tire with taller side walls per "back in the day." It sounds like it wouldn't throw things off too far. Crewzin I like the how the wheels look on your car.