Because of the side car Lara can only mount it from the right side. The motorcycle has no reverse gear, so to drive backwards Lara has to pull it back bit by bit using her muscles.
Throughout the Dead City levels Lara can collect a Nitrous Oxide Cannister in Citadel Gate and a Valve Pipe from the Trenches and combine them to obtain a Nitrous Oxide Feeder. After attaching it to the motorbike Lara can use the Nitro to jump big gaps.
There are some parts throughout the levels where you can use the bike to break through walls or floors. And, just like the Jeep it can be used to run over enemies like the SAS or Flying Beetles before they leave the ground.