Hi, welcome to Tribes! Unfortunately, you can't overdrive here. You've just gotta find routes that get you going the direction you want to instead of flying in from the front, magically twirling around, and going back the way you came
. However, disc jumping is a ton more useful in this game than rocket jumping seemed in my brief foray into Legions, so in a way that's the Tribes equivalent to overdrive. It takes some getting used to, but if used correctly you can gain a lot of speed and/or height (you can change the ratio depending on where you shoot and how fast you're moving) at the cost of health. It's useful for capping and practically a must if you plan on going heavy (good heavies use the shield pack, so they don't even get hurt when they dj).
Also, here's a post with some good advice for players new to the game, although I imagine you already know at least some of it since you play Legions: http://goonhaven.org/forums/viewtopic.php?f=4&t=157