speedometer drive/driven gear selection

[busterrm]

I have no problem with the calculations, but I cannot get it exact! Which is better, the number I arrive at to be larger or smaller than what the calculations suggest? My perfect number is ratio of 2.7759 , a 10/27 combo will give 2.7 or 11/31 will give 2.8181. Which one will give me the speed shown on the speedo to be just a little faster thanthe speed the car is traveling?

 

[Grumpy]

I've always preferred the speedo read I'm traveling a couple miles FASTER than I truly am, personally


theres calculators here in the links
http://garage.grumpysperformance.co...r-gears-at-the-transmission.12179/#post-59006

https://www.hotrod.com/articles/calibrate-gm-mechanical-speedometers/

http://garage.grumpysperformance.com/index.php?threads/speedometer-cable-90-adapter.1237/#post-43063

http://garage.grumpysperformance.co...the-speedo-gears-bye-redmen031.680/#post-8579

http://garage.grumpysperformance.co...correct-your-dash-after-rear-gear-swaps.1245/

 

[Loves302Chevy]

The calculated numbers (2.7, 2.8181) are the amount of reduction, correct?
If so, then the 2.7 would turn the speedometer faster than the 2.8181.
Or did I get this all backwards?

What will you do after a few burnouts and your tire diameter is now a 1/2" smaller?

 

[busterrm]

Haha!

 

[busterrm]

That (2.7 or 2.8181)is the drive to driven gear ratio in the transmission tail shaft.

 

[Loves302Chevy]

That (2.7 or 2.8181)is the drive to driven gear ratio in the transmission tail shaft.

Right, but the speedometer cable (output of the gears) must be slower than the input side, correct? As in - reduction.