What size speedo gears do i need if Im going from 273 to 342 ? (drive gear and driven gear for speedo)stock tire DIA . My car is a 1991 firebird formula 305TPI auto. Ive called trans shops and the GM dealer no one knows

 

Here you go steveusa, as you can see it depends on the tires as well as the transmission as to what you would use. BTW, this is out of a 1990 camaro GM service manual.

 

yes this wil be variable answer, it depends on much more than just axle ratio,

a stop watch and driving at 60mpg and timing yourself form one milemarker to thenext will tell you what you need to change


if at your 60mph you get to next marker before 60 seconds then you need to speed up the speedo cable

if you get to the next marker later than 60 seconds then you need to slow up the cable

smaller driven gear or larger drive gear will speed ujp cable

larger driven gear or smaller drive gear will slop up the cable

from factory most speedo's were not 100% accurate, they were real close though, it is not always possible to make speedo so accurate there are too may variable tire height and axle ratio and trans ratio variables


http://www.google.com/search?num=20&...edometer+gears


good luck