When running 205/60/13 yoko ao48 what's the exact distance of one complert revolution of the wheel?
I am wanting to set up my speedo but and know the diff ratio and the number of pulses per prop rotation but the measurements I'm doing are not accurate and differ with each one! Imsuppose tyre pressure will play a part too

http://www.superlite-wheels.com/yokohama.html

Are you sure you know have the correct axle ratio in your calcs?

I am fairly sure the Honda s2000 diff is 4.1:1

So can someone verify my calcs based on the info given?
1609= meters per mile
4.1:1 diff ratio
1.747 meters = rolling circumferance
6 pulses per prop rotation (6 bolts on prop)

6x 4.1 = pulses per wheel rotation.= 24.6 pulses
1609/ 1.747 = 921.007441. Which is meters per mile/ wheel circumference

921.007441 x 24.6 = 22,656.7831 pulses per mile

That looks right
Is there a place where you have to input 22,656.7831 then?

Yeah. The race technology dash 2 requires pulses per mile in either meters or inches!
As the speed sensor is on the prop with 6 bolts and diff is 4.1:1 the result is so large.
Would I be more accurate to calculate it in inches rather than meters

I don't think it is a math or setting problem more likely you aren't getting a clean 6 pulse signal per rotation of the prop, the only way to check would be to look at the signal with an oscilloscope

does the sensor have a small light to let you know its getting a clean reading?