I bought 15" x 8" wheels and wonder if I should get a slightly smaller diameter tire to slow the car down in order to be more accurate with my speedometer?
just get the proper speedo gear and be done with it.
when i set the aftermarket speedo in my old dart i had a Garmin on the windshield and a speedo app on my phone. a the end all three (car speedo, garmin speed reading and phone app) were all within a single mph at any given time.
