Sonic Riders is based around characters racing each other using devices known as "Extreme Gear", anti-gravity-equipped vehicles consisting of hover boards, hover skates, and hover bikes. Players compete to finish three laps around a racetrack before their opponents and complete the race in first place. Each race features up to eight characters competing. A key component of gameplay is the air tank, displayed in the lower right-hand corner of the screen. Air serves as the fuel for Extreme Gear, and is depleted gradually as the race goes on. Characters can also perform a Boost, which will give them a sudden burst of speed at the cost of a significant amount of air. If a player boosts into an opponent, their character will attack and stun the opponent for a brief period. Air is also more quickly spent using techniques like cornering, which allows the player to round sharp turns with ease, and building tension before a jump, which involves using the air to propel the player higher off of ramps. If a player runs out of air, their character will start running on foot; this prevents them from boosting, attacking, cornering easily or using charged jumps. Players can refill their air by performing tricks when jumping off ramps or off opponents' slipstream, with higher-rated tricks sequences restoring more air. Players can also collect rings scattered across the track; collecting a certain number of rings will cause their character to level up for the remainder of the race, increasing the strength of their attacks and extending their maximum air capacity.
Sonic Riders features sixteen playable characters, including guest characters from Nights into Dreams, Space Channel 5, and Super Monkey Ball. Each individual character has different statistics, altering their performance slightly in races, though some characters are restricted from using certain types of Extreme Gear. Characters are divided into one of three classes, each with different abilities: Speed, Power, and Fly. Speed characters can grind on rails, which grants increased speed and air. Power characters can break certain objects, giving the player a boost and additional air. Fly characters can fly through rings, boosting the player further into the course. Each race track features multiple shortcuts that can only be accessed by characters of a specific class. Players can spend the rings they acquire at the in-game shop to purchase new Extreme Gear, each of which possesses unique statistics and properties.
The game includes eight unique areas, each with two track variants, for a total of sixteen tracks. Nine tracks are unlocked through progression in the game's story mode, while two must be unlocked by winning Gold in both the World Grand Prix tournaments, in which players race through five consecutive tracks and attempt to get the highest overall score. The game's Story Mode is divided into two campaigns, whose events intersect with one another: The "Heroes" story, focusing on Sonic, Tails, and Knuckles; and the "Babylon" story, focusing on the Babylon Rogues, consisting of new characters Jet the Hawk, Wave the Swallow, and Storm the Albatross. In each campaign, players take part in consecutive races with predetermined characters, and must take first place in each race to continue the story. Completing the Heroes campaign unlocks the Babylon campaign, which includes an epilogue in which the two stories converge. Up to four players can also compete in the game's single race and battle modes.
Plot
Jet, leader of the thieving Babylon Rogues, observes the Key to Babylon Garden, an artifact and family heirloom said to unlock the secrets of their Babylonian ancestors. Doctor Eggman arrives and claims he can use the Chaos Emeralds to make Babylon Garden rise, asking for the Rogues' help in retrieving them. The Rogues agree and steal an Emerald, but run into Sonic, Tails, and Knuckles, who were also looking for the Emerald. Sonic gives chase, but Jet escapes with the Emerald. The next day, the three see Eggman on a digital billboard advertising an Extreme Gear race known as the World Grand Prix, with the Chaos Emeralds offered as the grand prize. When they realize that the Rogues are participating, Sonic and his friends enter as well.
Team Sonic and the Rogues compete in several races, but during the last race, Wave sabotages Sonic's board, allowing Jet to defeat Sonic and win the Grand Prix. Jet uses the Chaos Emeralds to make Babylon Garden appear, hoping to discover the legendary treasure of the Babylonians. Eggman steals the Key from Jet and heads for the garden, with Amy Rose grabbing Eggman's ship in an attempt to stop him. Sonic grabs a new board and pursues Eggman, but Jet challenges him to another race, seeking to defeat Eggman first. The two arrive at Babylon Garden and find Eggman, who is holding Amy hostage. Combining their powers, Jet and Sonic manage to retrieve Amy and the Key.
Jet uses the Key to open a secret door, leading the Rogues inside a Babylonian ruin. Team Sonic follows them inside, where they encounter the Babylon Guardian, a giant creature tasked with protecting the treasure. The two teams defeat the Guardian, causing a chest to appear. Eggman returns and demands they give him the treasure, but passes out in confusion upon discovering the treasure is only a carpet. Using the Key, Jet manages to make the carpet fly, revealing that the carpet is an early form of Extreme Gear. Team Sonic and the Babylon Rogues go their separate ways, with Jet promising to race Sonic again one day.
