EB 410 gearing

[pac]

I just ran my EB410 for first time.Bought this car used and in great shape.
Currently its geared 20/81. I have Reedy 510r blackbox,A 13.5t Revtech.
Local track is hard pack clay(They all run M4 proline primes or they sand down Proline shadows
Im thinking about lightening the car best possible and smaller spur (70t)Seems like good place to start(Along with tit ball studs ,shock bolts Etc)
20/81doesnt match up on any "charts"..Car seems to go pretty good as is.
My question is ,,with 70 t spur, Where do i start with pinion to get close gearing to the 20/81
Maybe charts are wrong..Maybe i am too nit picky..I would like to understand the gearing thing a little more everyday
Thanks everybody for input!!

 

[carolinagator]

81/70= 1.157

1.157 is our magic number. Reduce your pinion by the same number in the same manor.
20/1.157=17.28


A 17 tooth will be close.