Originally Posted by

**Bhodi11**
Im trying to do the math on the gear ratio's and FDR. Need Help.

The rear differential ratio is 1.8

92 spur / 46 pinion = 2 x internal ratio. The internal ratio is where im stuck. To get this im supposed to take the number of teeth on the differential spool pulley divided by the number of teeth on the layshaft pulleys. I think the number of teeth on the layshaft pulley is 19 but have no idea how many are on the differential spool pulley. Im thinking it is 38T which would give me an FDR of 4.0. Is this correct? Can anyone help me with the math? I was also hoping to plug the numbers in to a calculator to estimate top speed if possible.

From the Eryx part list:

401359 Pully solid axle 38T

401360 Pully middle 19T + spacer (3)

So you're correct, 38 / 19 = 2.0.

Edit: And internal * spur / pinion = 2.0 * 92 / 46 = 4.0

I can't help you with top speed, though.

-Mike