S4 gearing
 

Not much good at the gearing ratios :( i think i have the standard spur on and are going to fit a 13x2 so want to know the pinion size needed as a starting point plz :)

hmmm, never ran a 13x2 :eh?:

don't forget, its the same drivetrain as a BJ4 so those guys will be able to help.

thinking about it, I have never even run a brushed motor in one, only ever ran a 5.5 or a 4.5

I ran a 12x2 for the national at Stotfold last year on a 22 tooth pinion if thats any help.

Nice backheel there chris;)

22,23/78 should be about right, depending on the track of course

Cheers fella's ;)

I generally find the formula WIND + 10 works fairly well to gear brushed motors on the stock 78 spur.

So: (wind)13 + 10 = 23 teeth