Speedometer gear reference thread

[K85 Octane]

Lets try to run the same format, unless this thread already exists, which it probably does, but why not have another

I have a...
1989 700r4
1989 241
4.88 gears
38" tires that measure closer to 36.5" or 37" when hot

My speedometer gears are 15/40

Speedometer says 75 when I'm actually doing 70. Close enough for government work

 

[Blue85]

The transmission doesn't matter. Only the T-case gear, because not all tooth counts are available for all cases. Basically all mechanical speedos across brands are doing 1000 rev/mile. So the speedo gear ratio depends only on tire size and differential ratio.

 

[Idratherbedrivingablazer]

Hi, I've been trying to find some info/threads on speedo gears and only found this one. Can anyone help me. I have an '88 with 37's and 6" lift and just went from 3.42's to 4.88's. Runs and drives great but speedo says im doing 80 when I'm probably doing 55. How can I get it close to correct? any responses or direction to a thread would be greatly appreaciated. Thanks

 

[George_Pimpdaddy]

heres most the gear info http://www.transmissioncenter.net/speedometer_calibration_______va.htm

 

[Blue85]

Or you can take the ratio of your indicated speed to actual speed and multiply that by the number of teeth on the driven gear. That will tell you which driven gear you need. If it's not available, you have to look at a drive gear swap, which can be hard in a 208.