Originally Posted by
VooDooPH
running an old 12L3.... was wondering if anyone has tips on how to fit bigger pinion gears? currently running a 94t 64p spur and the biggest pinion i can fit is a 34. due to limited availability of smaller spurs, i'm looking if there's another way to get the gearing/roll-out i'm looking for.
Originally Posted by
Ophidian
I would try to find smaller spur gears. You could find some tires that haven't been cut down but that would affect the handling of the car.
To Ophidian's point, the only alternative is larger tire diameter...but I don't think he QUITE realizes just how large those tires will need to be. They would affect the construction of the car, not just the handling.
tire circumference X pinion teeth = roll-out X spur teeth
tire circumference = (roll-out X spur teeth) / pinion teeth
So, if you're running 17.5 brushless and want to shoot for, say, a 80mm-90mm roll-out with our given pinion and spur:
tire circumference = (85mm X 94 teeth) / 34 teeth
tire circumference = 7990 mm teeth / 34 teeth
tire circumference = 235mm (this kinda surprised me...no decimal amount. We ended up with a mm teeth number evenly divisible by the pinion teeth--believe it or not the odds against this were staggering. I'm headed off to buy a PowerBall ticket as soon as I finish this)
tire diameter = tire circumference / pi (an approximation, of course...our "perfect example heads, theoretically, off the rails at this point)
tire diameter = 235mm / pi
tire diameter = 74.8mm
That's a BIG tire...getting close to half again larger than a Touring Car tire. Jaco Prism's are start out at 48mm and most folks cut them down a few mm from there to reduce sidewall.
I'd go ahead and buy some smaller spurs.