Typical differential gear ratio = 3.29
Typical differential reluctor tooth count = 30
Typical input shaft reluctor tooth count = 25
97-03 tire rotations per mile = 781
"3.69" Drive sprocket ratio = 0.892
"3.29" Drive sprocket ratio = 1.0
"2.93" Drive sprocket ratio = 1.121
vss pulses per mile = differential reluctor teeth count X tire rotations per mile
vss pulses per revolution of the trans = differential reluctor teeth count / by differential gear ratio
Trans revolutions per mile = vss pulses per mile / vss pulses per revolution of the trans
Drive Sprocket Ratio = Drive sprocket size (In theory. See below)
As far as I can tell the only purpose of the drive sprocket ratio is to allow the pcm to calculate the actual transmission
rpm. This is because the sensor is on the input shaft so the pcm needs to know what to multiply the input shaft pulses by
to get the actual rpm of the transmission. Then the transmission can calculate shift times and slip with simple math.
Logically this makes sense but in reality every tuner including HPT refuses to modify the drive sprocket ratio. The accepted
method is to lie about vss pulses per revolution of the trans and trans revolutions per mile. I suspect it has to do with the
hidden table (Visible in tiny tuner) called calculated pulses per revolution. It appears to be the number of teeth on the input
shaft speed reluctor (25) divided by the final drive ratio. On a 1.121 sprocket ratio vehicle it is 22.30078. The only guess I
have is that both the calculated pulses per revolution AND the drive sprocket ratio need to be correct. Otherwise it will throw
off different transmission calculations. This would explain why everyone tends to just lie about the two values mentioned above
because it cancels out the incorrect values.
