According to http://www.miata.net/garage/tirecalc.html with 215/55/16 tires, the speedo reading is 1.3% slow so when it reads 60, you are going 60.8 so about 1pmh difference at 60 mph which is nothing really. I really want these to work so I can keep my 7 spoke rims which go really well with the car.
Thanks
brockley

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89 300E Pearl Grey Metallic
7 Spoke 16" staggered wheels (SLK)
215/55/16 Hankook Ventus HRII H405 tires
Euro Headlights
Smoked Corners
Smoked red/clear tail lights

1987 300e Black Metallic (mom's car)
8 hole 15" wheels (C Class)
Clear Corners
Red/Smoked tail lights