Tire Sidewall Height

[ew1usnr]

Thanks, Jeff.

6.5-13 overall diameter highway tread = 24.58"

Hmmm. I am trying to figure out the source of my speedometer inaccuracy.

I am running 175/80 tires (tread width mm / height aspect %) with a tread width of 6.875” and a sidewall height = 0.8*175 = 140 mm = 5.5 inches. With 13” wheels and 175/80 tires that gives an overall diameter of wheel (13) + tire (11) = 24". So, what I have is a little smaller than what was originally specified (24.58").


But, my speedometer reads 3 mph slower than my actual speed. My actual speed was calculated from a 24" wheel size and tachometer rpm plus observations of road side radar signs that say "Your speed is ..... " that were 3 mph higher than my speedometer. It is a puzzle that with a smaller tire/wheel diameter that my speedometer should be reading slower than actual speed. It should read higher.


PS: I really like the white roof on your wagon. My first car was 1963 four door Falcon wagon with a 170 and I still think that Falcons were the most nicely sized, styled, and designed station wagons that have ever been made. I love the roll down back window and the way the back seat flips around to make a flat surface and that the car has no blind spots. They are pure automotive perfection.