Grinding

Grinding (グラインド) is the act of balancing on a rail or something rail-like. Grinding is a big staple of the Sonic series in which characters can gain speed/momentum while on the rail. Grinding first appeared in Sonic Adventure 2 but can only be used by Speed Type characters such as Sonic or Shadow, also, those characters only wear Soap shoes in order to grind. Grinding is a must to defeat the Biolizard.

In later games, such as Sonic Heroes, Power Type and Flight Type characters can also grind. On top of that, the characters don't need to wear Soap Shoes in order to grind. Also, games before Shadow the Hedgehog required the use of balancing on the rail via control stick in order to properly maintain speed, this was removed possibly due to need for simplicity and possibly the fact that Sonic and Co. grew more experienced(along with the fact as of Shadow the Hedgehog rails have expanded somewhat in size and are less thinner). (Balancing is still used in Sonic Free Riders.)

In Sonic Riders and its sequel only Speed type Extreme Gears can grind on rails when it reaches a certain level. In Sonic Free Riders the grinding gear alone can be set for gears.

In Sonic Heroes, Shadow the Hedgehog, and Sonic 06, If the player presses the X button (Xbox/360), the B button (Gamecube), or the square button (PS2/PS3) the character will do a little spinning 180 hop on the rail which will make them go a bit faster. This no longer happens as the Boost can be used to go faster when grinding in the newer games. Although the flip can still be done for no effect in Sonic Unleashed, Colours and Generations by pressing either the B button (Xbox 360) or the circle button (PS3)

Grinding once again appears in all versions of Sonic Generations. However, it not only appears in stages that originally had rails, it appears in some stages without it in the past, such as Mushroom Hill.