The first Sidecar TT race was run in 1923 over three laps of the Mountain Course, covering 113 miles. Freddie Dixon and passenger T.W. Denney won aboard a special Douglas banking-sidecar at an average race speed of 53.15 mph. The term "banking-sidecar" referred to a design that allowed the sidecar body to lean with the motorcycle through corners, a notable technical innovation for the era.
The class did not run continuously from that point. For 1926, both the Sidecar TT and the Ultra-Lightweight TT were dropped from the programme due to insufficient entries. The sidecar race did not return as a regular fixture until 1954.
When the Sidecar TT was reintroduced in 1954, it ran on the Clypse Course rather than the full Mountain Course, and was restricted to machines with engines not exceeding 500cc. More significantly, from 1954 through 1976, the race counted toward the FIM Grand Prix motorcycle racing World Championship, making it one of the few world championship events conducted on public roads after the Isle of Man TT's broader departure from that status.
From 1960, the world championship sidecar TT events transferred to the full Snaefell Mountain Course, maintaining the 500cc engine limit. A non-championship 750cc class was introduced alongside the championship race in 1968, reflecting demand for a larger-engined category. By 1975, both the 500cc and 750cc limits were replaced by a single 1000cc engine capacity class. The following year, 1976, marked two changes: the event became a two-leg race, and it was the final year the Sidecar TT formed part of the world championship.
The current Sidecar TT runs under Formula Two regulations first introduced for the 1990 event. These specify two-stroke engines not exceeding 350cc or four-stroke engines not exceeding 600cc, with the four-stroke four-cylinder production-based engine being the dominant configuration in contemporary competition.
Technical regulations define precise dimensional constraints: maximum overall width of 1575mm, maximum wheelbase of 1651mm, a track between 800mm minimum and 1105mm maximum, and a maximum height of 800mm. Minimum weight without fuel is set at 136.5kg, and ballast may not be added to reach the minimum. All three wheels must be independently braked using ferrous brake discs. Slick tyres are permitted.
The sidecar may be placed on either side of the motorcycle, but hinged sidecars and steerable sidecar wheels are prohibited. The main chassis frame must be constructed from steel tube to prescribed specifications, and monocoque and composite construction of the frame is forbidden, with the single exception of the sidecar platform itself, which may use aluminium or carbon fibre skinned honeycomb material.
Passengers in TT sidecar races must hold a TT Course Licence as a passenger, a separate qualification from the rider's licence, reflecting the distinct skill and physical demands placed on the third wheel occupant who acts as mobile ballast and stability element through the course's corners and elevation changes.
The outright sidecar lap record on the Mountain Course stands at 18 minutes 45.85 seconds, an average speed of 120.645 mph, set by Ben Birchall with passenger Tom Birchall during Race 2 in 2023. The same pair set the race record at the same event: 56 minutes 41.816 seconds across three laps for an average race speed of 119.784 mph, improving on their own previous race record from 2018.
The Birchall brothers have been the dominant force in modern sidecar TT competition, accumulating multiple victories across both legs of the two-race format. Their consistency has driven the progression of lap records through the 110 mph and then 120 mph barriers.
Sidecar racing at the TT retains characteristics that distinguish it sharply from both solo motorcycle racing and from sidecar events at permanent circuits. The Mountain Course's 37.73 miles include public roads, stone walls, hedges, and buildings at close proximity, with no run-off in many sections. The weight distribution and cornering dynamics of a three-wheeled outfit respond very differently to camber, gradient, and surface changes compared to a solo machine.
The passenger's role is physically demanding and tactically significant. By shifting body weight through corners, passengers can influence how the outfit rotates and how the third wheel loads and unloads. Effective communication and synchronisation between rider and passenger, established over years of practice laps and partnership, is considered as important as mechanical preparation.
The two-leg format means that cumulative timing across both races determines the overall result, adding a strategic dimension around risk management and consistency that single-race formats do not produce.