My speedometer is way off. I have a 1970mav that came with a three speed manual transmision (same cable and gear as when we got it) and we put in a c-4 transmision from a 77 mav along with the rear end from that car. we have 15in wheels on the back and 14s on the front. My speedometer is reading about 20 miles slow when i am going 60mph. I have tried the equations that I have found and they say I need a 28 tooth gear for it to be right but they only make the gears up to 21. Am I using the formulas wrong or just not finishing them?
http://www.tciauto.com/Products/TechInfo/speedo_gears.asp I think your off with your numbers. I run 4.11's and use a 23 tooth gear and its pretty close. You should be going the other way if your speedo reads lower than actual. Did you input rim diameter instead of tire diameter??
Im thinking its the wheels, what did your car originally come with??? i had 14s on my car and at 70 i was going 60, changed to 15s in the back and the problem dispeared. But that would mean your car came with 16s... impossible!
the original tire size on the 70 was 13 inch and i now have 15s (235 60 15) on the back. I don't know the gear ratio, all i know is that it is an 8 inch rear end and it came with a 302 v8 in 1977.
tires and wheels are 2 different things... "the original tire size on the 70 was 13 inch and i now have 15s" in this case...the 26.10 inch tires would be twice as tall as the "13 inch tires" you had... the '70 should have had...14" 4 lug wheels... the tire size is what makes the difference...in the speedo being off...
Take a look at this calculator to see wheel and tire size impact on speedo. http://mmb.maverick.to/showthread.php?t=39234
