Quote:
Originally posted by Dennis
You can determine the amount that your speedo is off by finding the circumference of your current tire/wheel combo and comparing it to the circumference of the factory tire specs.
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Note below the 78 aspect ratio, stock tires in the 70's were 165SR15 which can be translated to an 80 but 78 is more accurate. A larger overall diameter will slow the speedo down and a smaller diameter will speed it up.
135/78R15 = 23.29
145/78R15 = 23.91
155/78R15 = 24.52
165/78R15 = 25.13
195/50R15 = 22.68
205/50R16 = 24.07
205/40R17 = 23.46
215/40R17 = 23.77
225/35R17 = 23.20
235/35R18 = 24.48