Speedometer Calculation

You can use this conversion table to calibrate your speedometer: http://tire-size-conversion.com/speedometer-calibration/ OR you you can reprogram the ECU to make the MPH correct on the gauge with a tool like this: http://www.hypertech-inc.com/products-speedometer-calibrator.aspx

After entering your tire sizes, you're only about 2 mph off (slower) on the MPH gauge than the stock tires. Not much to worry about unless you want to get the speedometer dead accurate. Going from a 70 to a 65 series is not a huge jump so it's not that far off.

When I calculated it from http://tire-size-conversion.com/speedometer- calibration it says + 2 mph not - 2 still not a major difference, but you stated (slower).

Ahhh.. Sorry about that. Yes you are correct. My mistake. Smaller tires = faster speedometer. Thanks for the correction.