The Sidecar TT first ran in 1923, covering three laps (113 miles) of the Mountain Course. Freddie Dixon and passenger T.W. Denney won that inaugural event aboard a special Douglas banking-sidecar at an average speed of 53.15 mph. The race was dropped after 1925 due to a lack of entries and did not return until 1954, when it was re-introduced for machines not exceeding 500 cc engine capacity, run on the shorter Clypse Course.
The event moved to the full Snaefell Mountain Course in 1960 and became a round of the FIM World Championship, a status it held through 1976. A non-championship 750 cc class was added in 1968, and from 1975 the old 500 cc and 750 cc divisions were merged into a single 1000 cc class. In 1976 the race adopted its current two-leg format. The 1990 edition introduced the FIM Formula 2 class for sidecar outfits, specifying two-stroke engines up to 350 cc or four-stroke engines up to 600 cc, a framework that has governed the race in the decades since.
The Sidecar TT runs as two separate legs on different days of the festival, with overall results determined on aggregate time. Entrants must hold a valid National Entrants or FIM Sponsors Licence for Road Racing, while sidecar passengers are required to hold a TT Course Licence specifically as a passenger.
Under current Formula 2 regulations, machines use production-based motorcycle engines of 501 to 600 cc in four-stroke, four-cylinder configuration. Rotary engines and electronic traction control systems are prohibited. The sidecar may be placed on either side of the motorcycle, and hinged sidecars or steerable sidecar wheels are not permitted. Minimum weight without fuel is 136.5 kg, and the addition of ballast to reach this minimum is prohibited. The maximum overall width is 1,575 mm and maximum wheelbase is 1,651 mm.
Official qualification requires completing the lap within 115 percent of the time set by the third-fastest qualifier in the class.
The lap record for the Sidecar TT stands at 18 minutes 45.85 seconds, an average speed of 120.645 mph (194.159 km/h), set by Ben Birchall with passenger Tom Birchall during Race 2 in 2023. The Birchalls also hold the race record at that event: 56 minutes 41.816 seconds for three laps, an average race speed of 119.784 mph (192.774 km/h), bettering their own previous race record from 2018. The Birchall brothers have been the dominant force in the modern era, repeatedly raising the speed ceiling on the Mountain Course.
The Sidecar TT occupies a unique place within the TT festival as the only class that requires a two-person crew, placing crew coordination and physical teamwork at the centre of the competitive challenge. The passenger — often called the monkey — moves their body weight to help balance the outfit through corners, a technique that has been refined over the century the event has existed.
The race's world championship years between 1954 and 1976 attracted the leading continental sidecar exponents of the era, adding an international dimension that went beyond the traditional British and Irish road-racing community. Since the withdrawal of world championship status the event has retained its prestige within the specialist sidecar road-racing world, drawing dedicated crews from across Europe who regard the Mountain Course as the ultimate test of their craft.
The transition from the Clypse Course to the Mountain Course in 1960, and from open-capacity to the standardised Formula 2 regulations in 1990, mark the two most significant structural changes in the event's history. Both shifts prioritised closer competition and improved safety management, allowing the Sidecar TT to maintain its place as one of the most demanding and distinctive events in the Isle of Man TT programme.