Yes it is a freemium title & is stock full of in-app purchases but so far I've managed to play without any paywalls. I've unlocked the second bike 'Tango' & I'm currently upgrading so I can take on Butch.
It has the same one not go appeal of the XBLA games just a shame the leaderboards are UPlay registered. Gamecentre leaderboards would have been better.
You use fuel for each track you race & this replenishes over time. Parts are needed to upgrade bikes which you get from a roulette wheel when completing a track.
A world map unlocks new tracks when you complete various missions.
I've got quite a few silver times but not a single gold yet. I think these will come with more bike upgrades.
Now to go find my UPlay username & password ...