As with all Mad Skills games, all bikes and upgrades can be unlocked by playing for free! The more you play, the more gold and silver coins you'll earn. Here are some tips to help you get the most coins and gold in the quickest time possible.
Achievements can be found in a tab on the player profile
Completing an achievement will reward gold coins
Play in the Daily Dash
Beating the Daily Dash challenge each day will give you silver and gold coins.