The Taigen 4:1 steel gears are a perfect match for a Tiger; you'll slow it down nice and they're very robust.
Not sure if Curtis has them yet.. but Taigen might soon, and other vendors already do. Welsh Dragon Models (UK), rctank.de (Germany), or tank army in Australia.
Tiger I - Panzer III - Panzer IV - Chi Nu Kai - Panther G - KV-1b 756(r)
M4A3(76) Sherman - T-34/85 - M3 Grant