Readjusting the speedo reading?

[Hilush]

Does anyone know of any equation to work out how to get the right drive cog for the speedo after you have changed diff gearing,gearbox and wheel size to get the speedo accurate again?

[dumbass]

if u have 20 teeth on the gear
and u goto 19 well I make speedo go faster by about 5%

[benjamin]

If you have an electric speedo sender, get the speedo corrector kit from jay car and follow the instructions. Simple as. I used a GPS speedo on my phone to calibrate it. If the sender is mechanical, do what dumbass said.

Also work out what percentage you are out by.

For mechanical sender, if you are indicating 110 but actual speed is 100 then you need to slow down the sender by 10% (need a bigger cog). Therefore, if the cog has 20 teeth it needs to have 10% more teeth so 20 x 1.1 = 22

And for personal preference I would try to keep indicated speed a little bit higher than actual speed