Ok, this is not exactly a trick, I would rather call it an easter egg (probably not intentional!). 

Yesterday I lost the car in an usual point of AR Offical track. You should aim for the right side of the bridge, somewhere near it, at high speed (higher than this pic, let's say 170-180 kmh).
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But, instead of the usual bouncing against the barrel, the car jumps over it (!!!) and suddenly I found myself out of the track, and my car still working 
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Well.... that hill is there just to say "climb me" 
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Here we go!!! And upside the hills, some rough rally setting was just waiting for me!!!
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I believe I can fly!!
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Come oooon! Jump higher!!!!!
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It works with other cars too! yeah look at the pegeaut 
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... but this Honda really sucks on the grass!! 
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This "glitch" can't affect lap times, even if there should be some shortcut (and I haven't found it), anyway the lap times will count all the time you spent off the track. So it's just for fun and kidding 

I hope the Devs are not canceling this glith in future updates. Instead they should improve this kind of stuff, making a sort of bonus track or a simple easter egg at least. Something like: "Congrats! You have found the secret rally path #1!" Then add a couple of flags which delimitate some track and we will have a dirty track for practicing 

...Can't wait for the REAL rally update!!!