A rumpshot of Mayor Flitter Flutter riding a standard bike from Mario Kart Wii. Sorry if I got some details on the bike wrong, I couldn't find many references for that angle.
The idea grew from her riding a scooter in Twinkle Wish Adventure. I can't remember seeing many modern ponies riding bikes.
I've grown out of this phase, so you won't be seeing very many rumpshots from me nowadays.