While most of the suspension arms were in common with Lotus 22, the angle of the rear radius arms on the plan view was different from the narrower-frame Lotus 22, so they were not interchangeable with the 22. On the frame structure, the lower side pipes and the width-wise lower pipe behind the cockpit were rectangle tubes, with most of the other frame pipes being round steel tubes in various diameter. The upper left round pipe was used as the water feed pipe (the use of anti-freeze chemicals was prohibited by most of the race organisers at the time for the danger of making the tarmac slippery) for the radiator up front, and the lower right side pipe and a half of the width-wise lower rear cockpit pipe were used as the return path. Likewise, the upper right side pipe was the oil feed to the oil cooler, and the lower left tube was the return. This frame was mostly made by Arch Motors, carrying 'AM' serial number. This water/oil-bearing frame configuration was shared with Lotus 22 and other later Lotus formula cars, but the combination of a wider and thus larger radiator, wider and bulkier steel frame acting as a cooling device, and the small displacement engines resulted in more than ample cooling capacity. Atypical of the contemporary racing cars, Lotus 23 models sometimes experienced an over-cooling problem when the thermostat was not installed in the coolant circuit in sprint races, and displayed a very stable water/oil temperature in endurance racing. The 23B The 23B in 1963 had the original center gear shifter relocated to the right side of the driver, and the radiator and oil cooler were combined into a single unit, with the lower 1/5 or so acting as the oil cooler. The frame received additional structural tubes to take the torque of Lotus TwinCam-based 1.6 litre Cosworth Mk.XII and Mk.XIII, mated to "high torque spec" 5-speed Hewland Mk.V transaxle. Smaller displacement engines were mated to 5-speed Hewland Mk.IV. Both the Mk.IV and Mk.V transaxles had GKN (Ford Zephyr) differential gears and a forward-facing selector rod on the right side in a bespoke (Hewland made) tail casing. The intake funnels on the Weber carburetors on 23B (and the 23C) were housed in a "cold air box" which received fresh air from two oval holes cut out on the top side of the rear body behind the driver.