Feel free to share if you find any new tricks here!

Restart trick: The very first attempt at a track for some reason allows you to turn sharper at the start. So exit out the level and re-enter it each time instead of pressing the retry button. This is useful on any level where you need to turn at the beginning such as Welcome!, Collect, Around etc.

Snowball courses trick: On Hollow and Cold there are snowballs which you can move out the way of the path however when you press the restart button they go back to their original positions. You can avoid this and clear them out the way by forcing your car to flip over and wait until it respawns you automatically. The snowballs wont return. It's easier on Hollow since you can head to the bowl on the left and drive up the fence to flip yourself over.

Ramp glitch: Useful for Half-Eight, I'm not sure what triggers it but you can fall off the ramp at the start quicker. I did this by randomly driving up against the rails at the end of the track and upon restarting the car will go over the ramp a lot quicker. This effect only goes away after you exit the level. Something similar seems to happen on the Beyond track that makes you drop off the ramp quicker.

Undercup glitch: I've tried recreating it but to no success. I believe this glitch can happen on pretty much any course but it is only faster on some like Undercup where the finish line is close to the start line.

ZigZag glitch: I've only seen this work on the track 'ZigZag', but for some reason on this level if you reset while colliding with one of the barriers, instead of spawning parallel with the rail you spawn pointing diagonally left, allowing you to turn much quicker and gain 2-3 tenths. The best way of doing this is to reset normally, then drive straight into the grassy patch on the second barrier, although I've seen it trigger on most of the others. My guess is that the spawn point is too close to the yellow rails so the game gets confused and tries to move you away from the rail.

Tight-turning trick: It's possible to make a tighter turn than usual if you first tap in the opposite direction before quickly holding down the desired direction (i.e. for a tight right turn, you would briefly tap on the left side of the screen before immediately holding down on the right to turn right). This is usually faster as you spend less time in the turn and can start accelerating again sooner, as well as allowing you to beeline for the corner.

De loop : it is possible to cross the backdoor fence at thé start and cut through thé fields thé cross thé finish fence again

Plenty Flip Restart: There seems to be an invisible bump or something just behind the starting area in the track Plenty (see my PB), I have no idea if there could be a consistent way of doing it, but plenty of people on the iOS leaderboards seem to have found it as well, and I have gone over it without flipping once before, so maybe it's doable?

Switchboard : The secret is to tip the car by driving to the left of the last yellow button and moving to the left so that when the platform tips the car tips over and then restarts at the start, at the time of this second start the platforms are already tipped over so saving time

Ice: it is possible to go over the barriers by going to the barriers in front of the starting line and giving a right hand drive. See my run at 3sec41

The record of Half-Eight is 3sec96, I think it was made with the same method it must be possible to go over one of the two round barriers by taking the right angle