Well the stock rear-end ratio is 3.31
The stock ratio of the 3 speed in high gear is 1.53 to 1
Kershaw Direct drive is 45 diff gear with a 18 tooth center gear=2.50 to 1
If you use all of these numbers, compare your old setup with your new setup, or just pick a speed you want to run, you can then pick your pinion size.
I need to run a 27 tooth (from a previous 16 tooth) to mantain the same speed (48 mph)
I'm also running a Neu 1515 1Y on 4s until my 6s shows up in the mail.
Well, I don't have an old setup to compare it to, lol. I just ordered my brushless setup and the gearbox at the same time. I was running a nitro before, and I don't know what kinds of loads the electrics can handle before overheating, which is why I was asking.