MM5700 in Losi XXX-T

[BrianG]

Can't answer your gearing question as I'm not familiar with that vehicle, but whether you need a UBEC or not is determined by the main battery pack voltage. If you are running over 8 cells or 3s lipo, get a UBEC.

And in case you don't know; a BEC is basically justy a votlage regulator which converts the main batter pack voltage to 5 or 6v for your receiver and servos. The BEC in most ESCs are linear, and will heat up a lot if using higher cell counts. The UBEC is a swithincg device so it runs much cooler and more efficienty.