Lotus 23

The 23 used a wider version of the Lotus 22 space frame, with the lower side pipes and rear crossmember in rectangular tube and most other members in round steel tube of varying diameter. Notably, the upper left round pipe served as the water feed to the radiator, the lower right side pipe and part of the rear cockpit cross-pipe formed the return path, while oil feed and return ran through the upper right and lower left tubes respectively — a water and oil-bearing frame configuration shared with the Lotus 22 and later Lotus formula cars. Front suspension was double wishbones with outboard coil-damper units using Triumph uprights made by Alford and Alder, with Triumph Herald rack-and-pinion steering and outboard Girling disc brakes. The rear used top link and reversed lower wishbones, radius arms, and halfshafts with Metalastic rubber joints that carried no cornering load. The car was originally intended for engines between 750 cc and 1,300 cc with a Renault four-speed transaxle, but production examples mostly used a five-speed Hewland Mk.III.

The 23 complied with FIA rules by incorporating regulation trunk space to the right rear of the driver, windscreen wiper, horn, paired headlights and tail lights, a rear number plate light, cable-operated handbrake, and spare tyre mounting under the front body.

The 23B of 1963 relocated the gear shifter from the centre to the right side of the driver and combined the radiator and oil cooler into a single unit, with the lower fifth acting as oil cooler. The frame was reinforced to handle the torque of the 1.6-litre Cosworth Mk.XII and Mk.XIII twin-cam engines mated to a Hewland Mk.V transaxle. Smaller engines used the Hewland Mk.IV. The 23C was developed to accommodate wider Formula Two tyres on six-stud magnesium wheels, with the body extended accordingly to cover the broader rubber. Approximately 130 examples of the 23, 23B, and 23C combined were made in period, though the model's popularity led to many additional cars being assembled from reproduction and replacement parts; estimates of the total number including these range between 200 and 400.

The 23 debuted at the Nordschleife on 27 May 1962 in the 1000 km of Nürburgring. Jim Clark, driving a works car with a 1.5-litre Cosworth Mk.X engine rated at around 100 bhp, stormed through a wet opening lap to lead the race by 27 seconds over Dan Gurney's Porsche 718GTR despite the Porsche having nearly four times the Lotus's power. Clark extended his lead on each lap until the track dried, but was overcome by exhaust fumes from a damaged manifold on lap 12 and crashed out. A second 23, entered by Ian Walker Racing and driven by Peter Ashdown and Bruce Johnstone with a 997 cc pushrod Cosworth Mk.III, finished eighth overall and won the 1-litre sportscar class, beating class winners from the 3-litre prototype and 1-litre prototype categories as well as outright larger-engined cars including a Ferrari 250 Testa Rossa.

Two 23s were entered for the 1962 24 Hours of Le Mans, one for Les Leston and Tony Shelly with a 742 cc Coventry Climax FWMC, the other for Jim Clark and Trevor Taylor with a 997 cc Cosworth Mk.III. The cars failed to pass scrutineering on multiple grounds including insufficient windscreen height, excessive fuel tank capacity, too large a turning circle, insufficient ground clearance, and failure to meet the spare tyre regulation. Most issues were resolved by makeshift modification, but the spare tyre question proved insurmountable. The cars carried different-diameter front and rear wheels and thus a front spare could not substitute for a rear flat tyre. Lotus had new four-stud rear hubs machined overnight and flown to Le Mans, but scrutineers rejected these on the grounds that the original six-stud design must have reflected a structural requirement, making the four-stud version unsafe. The ACO did not change its position even when Lotus engineer Mike Costin offered to provide structural calculations demonstrating adequate safety margin. Colin Chapman vowed that Lotus would never race at Le Mans again — a promise the company kept until 1997, long after Chapman's death in 1982.

In the aftermath, Chapman worked with Alpine through Gérard Crombac to help the French constructor develop what became the Alpine M63, itself based on a Lotus 23-derived frame design by Len Terry, Bob Dance, and Keith Duckworth. The M64 that followed won the Index of Thermal Efficiency at Le Mans in 1964, partly as a consequence of the 1962 ban.

The Lotus 23 established itself as a "giant-killer," regularly defeating cars from larger classes in period competition. Its reputation attracted a restoration movement from the early 1980s, with parts remanufactured and a Register established that is now part of the Historic Lotus Register in the UK. Several replica manufacturers have produced continuation cars, among them Xanthos Sports Cars in Liverpool (later Niagara Falls, Canada), whose Xanthos 23 exactly replicates the 23B frame design, and Lee Noble's 1996 version with a wider track for modern tyre sizes, which sold more than 60 examples. The 23 remains a staple of vintage racing in Europe and the United States.