Jul 2

Jul 2 Guide: Mercedes-Benz C111-I

Mercedes-Benz - Mercedes-Benz C111 - 1960s German Cars - 1960s Supercars - 1960s Concept Cars - 1970s German Cars - 1970s Supercars - 1970s Concept Cars

Background

When Mercedes-Benz unveiled their mid-engined C111-I at the Frankfurt Motor Show in September 1969, it garnered massive attention and interested parties began lining up to buy one.

The elegant W113 SL introduced in 1963 had proven enormously popular, but did not offer the same level of performance as its famous predecessor - the W198 Gullwing and Roadster.

By 1969, the W113 was nearing the end of its production life and it seemed natural to assume the startling new C111-I might take its place.

Unfortunately though, this was not to be the long-awaited successor to the iconic 1950s Gullwing.

Despite appearing almost production-ready, and with the high standard of fit and finish one would expect of a Mercedes, the C111 was created purely for research and development. Not even blank cheques from several wealthy individuals could convince the firm to change their mind.

Instead, the objective was to test new propulsion concepts and production methods.

Mercedes had first trialled a rotary-piston engine in late 1965 and wanted to establish once and for all whether the patented Felix Wankel design was the future of combustion engines.

They also used the C111 to experiment with bodyshells manufactured from glass-reinforced-plastic (GRP).

Chassis

The C111-I comprised a sheet steel monocoque chassis with a 2620mm wheelbase. To this, the GRP bodyshell was riveted and bonded in place.

Torsion bar suspension was independent all round; double wishbones at the front and an advanced triple wishbone multi-link arrangement at the back.

Anti-squat and anti-dive controls were installed along with vacuum-assisted ventilated disc brakes from the 6.3-litre W109 300 SEL.

Each sill contained a 60-litre fuel tank.

Fuchs 14-inch cast alloy ‘Mexican Hat’ wheels were switched to ATS ‘Penta’ five-spoke rims for the C111-I’s motor show debut. They were both originally shod with 195 VR 14 Dunlop Racing tyres.

Engine / Gearbox

Mounted transversely in the chassis was a three-rotor Wankel engine designated Type M950F.

At the time, many manufacturers had an interest in Felix Wankel’s unconventional powerplant, but Mercedes were ready to push the rotary-piston format to its limit.

Compact and quiet compared to traditional reciprocating-piston engines, the motors installed in the C111-I and subsequent C111-II were at the zenith of Wankel technology.

Three rotary piston chambers of 600cc gave an overall displacement of 1800cc.

With compression set at 9.3:1 and mechanical Bosch fuel-injection, the Type M950F produced a peak output of 280bhp at 7000rpm. The torque rating was 217lb-ft between 5000rpm and 6000rpm.

As dual ignition proved difficult to adjust, single ignition was adopted.

The five-speed transaxle comprised a ZF 5DS-25/1 gearbox with triple-plate clutch and limited-slip differential.

Bodywork

Six examples of the C111-I were built, often with slight detail variations from one example to the next.

The C111-I’s futuristic styling was created by chief designer, Bruno Sacco.

Although not the first mid-engine Mercedes-Benz concept, this new car was a complete departure from the SL-X produced in early 1966.

Sacco’s creation featured a sloping nose with retractable headlights located either side of a radiator cooling grille that was variously given a brushed alloy or matt black finish.

Supplementary lights were housed further down the nose underneath clear plastic covers.

The lower body was painted matt black to give the C111-I a slender profile.

Sacco incorporated Gullwing doors, each of which was equipped with a pair of pressurised hydraulic struts.

An unconventional clap hands wiper layout was used to clear the panoramic windscreen.

Side windows could not be lowered, but a vertical hinge allowed the rear quarter section to open outwards.

Some early C111-Is used a fastback rear windscreen, but this was soon ditched in favour of a small vertical screen with a flat rear deck and flying buttress sail panels either side.

Each sail panel housed a large bank of engine cooling vents that were variously finished in matt black or body colour. Some later examples had cut down vents that allowed the upper portion of the buttress to remain open.

A Kamm tail gave the C111-I a very short rear overhang. Aside from the rear face of the body-coloured engine cover (hinged at the trailing edge), the tail fascia was dominated by a full-width matt black grille. Either side of this were banks of three stacked light clusters.

The first few prototypes were painted metallic white, but all subsequent C111-Is were finished in ‘Weissherbst’ metallic orange. The GRP bodyshell meant the finished car was very light and stable.

Several of the C111-I’s design features were adopted by other manufacturers, most notably the retractable headlights mounted above clear panels for auxiliary lighting. This layout was used on both the Lamborghini Countach (designed by Bertone) and the Ferrari Berlinetta Boxer (Pininfarina).

The Ferrari also incorporated a full width nose-mounted grille similar to the C111-I plus its two-tone livery where the lower body sections were painted matt black.

Interior

Inside, the C111-I displayed at Frankfurt certainly did not have the feel of a development test bed.

In typically Germanic fashion, it was very well laid out.

A boxy dash extended across to the passenger side of the cockpit.

A speedometer and rev counter were housed directly behind the steering wheel. Supplementary gauges were located off to the right and air-conditioning vents were littered all around.