Lotus Mk IX

X-ray spec

This car was Colin Chapman's first since he'd turned professional. His then-technical director Mike Costin guides Keith Howard around it

As all of us born in 1955 will attest, it was a good year. In the case of Lotus Cars for 'good' read 'transitional' – in the sense of growing up. Until then Lotus had been a part-time enterprise for founder Colin Chapman, who still had a day job at British Aluminium. Likewise, the unsung group of enthusiasts who worked alongside him – the likes of Mike Costin, Peter Ross and Gilbert 'Mac' Mackintosh – had done so for the buzz.

From 1955 that would begin to change. Secure jobs elsewhere began to be traded for less certain but more exciting ones at Hornsey. Chapman opted to work full-time at Lotus alongside chief mechanic – and soon to be technical director – Mike Costin, who had chucked in his job at de Havilland's.

Two Costins were to play a central role in early Lotus successes: Mike and his aerodynamicist brother Frank, who for the time being remained at de Havilland. Efficiency lay at the heart of Chapman's design philosophy, aerodynamic efficiency no less than mechanical. For a wind-cheating advantage he looked to Frank, who knew nothing of racing car aerodynamics to begin with but methodically turned it into a precise science.

Frank Costin would later offer up the prayer, "Save me, oh Lord, from the statement: what looks right is right." Aesthetics were of no concern to him; that a car's form should follow its aerodynamic function was. So you can understand the trepidation with which Chapman watched the Mark VIII, the first Lotus to be shaped by Costin's calculations, taking form. With its manta-ray front end, spats over the rear wheels and large tail fins, it looked so outlandish that Chapman began to doubt that he could sell it – until, famously, someone showed him a picture of the new Mercedes W196 Formula One car.

Chapman ordered a more flexible, more practical development of the Mark VIII for 1955, to be called (of course) the Mark IX. Superficially similar and requiring only refinements to Costin's shape, it had improved rear suspension and offered easier access under its enveloping bodywork. It would become one of the notable early Lotus success stories.

Part of its appeal came from the range of specifications on offer. If your pockets were deep enough you could have a Coventry Climax FWA engine, de Dion rear suspension and, eventually, disc brakes. If finances were tighter you could still be competitive in club events with a Ford 10 engine, Ford live axle and Girling cable brakes. Those who admired the Mark IX's revelatory handling and aerodynamics but craved more oomph asked for a car able to accept a larger engine, and were duly rewarded with the Mark X.

Frank Costin died in 1995, but his brother enjoys a busy retirement. Curiously for a man who was a lynchpin at Lotus until he left in 1962, he candidly admits: "I've got no interest in motor cars at all, and never did have. That was work, remember. All my life I've been interested in engineering and things technical, it doesn't matter what they are. It just struck me that with aeroplanes you never saw the whole thing, whereas with a car you could get involved from start to finish."

X-ray spec: Lotus Mk IX

Both the works Mark IXs — 9 ENX and XPE 6— had lightweight bodies. The MG-engined car, 9 ENX, was the only IX built with magnesium panels, while the Climax-engined car, campaigned by Chapman himself, had aluminium of a thinner gauge. "I think the body was 20 gauge rather than 18 gauge, so it weighed 25 percent less — a saving of 15lb," explains Mike Costin. "Many of the drivers were no lightweights and should have taken a stone off, too."

Although the Mark IX's spaceframe has been eulogised as an exemplar of the art, Mike Costin (who co-wrote the 'bible' on the subject with David Phipps) doesn't regard it as exceptional. "Chapman never solved the problem of the driver compartment," he says. "If you'd had diagonals to complete the structure in that area you could have done better, but it was virtually impossible to accommodate the driver and meet the dimensional requirements. You had to comply with these for the internationals. I remember that a scrutineer at Le Mans wanted to kick us out for having incorrect dimensions but I measured his piece of wood and it was the wrong length. I cut the end off and said, 'Now try that!"

To keep the front of the body aerodynamically clean the IX had novel pivoting headlights which could be raised into position when required. "They were never going to be used, except at Le Mans, but the regulations said you had to have them. Actually, the scrutineers at Le Mans didn't like them, but then they didn't like anything to do with Lotus." Despite the tragedy at the 1955 Le Mans and Chapman/Flockhart being disqualified in the race, Lotus celebrated its first appearance at La Sarthe by renaming the top-spec IX the 'Le Mans'.

To minimise drag Frank Costin paid particular attention to ducting air to and from the radiator. "The air was ducted into a low-pressure area under the car, so that there was a pressure difference between inlet and outlet." The arrival of disc brakes meant the amount of air ducted to the front wheels could be reduced, so FC developed a smaller, optimised inlet for XPE 6 that became a standard feature on future Costin designs. The efficacy of his design concept was confirmed when John Bolster tested XPE 6 for Autosport: it reached 128mph with its meagre 75bhp.

The next generation of Lotus racing cars, from the Type 12, would be fitted with the trademark 'wobbly web' cast wheels, but the IX still used classic Borrani wire wheels. "The Borranis were okay, just expensive [about £16 each]. With either Dunlop or Borrani wheels you had to have the expensive splined hub, and the wheel nuts weighed a ton. Coopers had used magnesium wheels for years, and Charlie Cooper used to reckon he made more money making and selling wheels than he did on the rest of the car. That sort of thing would light up Colin's eyes — he was the best plagiariser in the world."

Cutaways behind the front arches, to improve brake cooling, were the result of aerodynamic tests on the Mark VIII during which Frank Costin was strapped to the bonnet and driven up and down a Cheshire airfield. "Colin and I did the driving and Frank did the laying on the bonnet! He couldn't have done that with the Mark IX works cars, neither of the bodies would have stood him. The wool tufts he was watching were all underneath the wheel arch — he wanted to see which way the wind was blowing behind and inside the wheel. We were getting up to 100mph or so."

XPE 6, and maybe some other IXs, were fitted with an unusual rack-and-pinion gear to replace the standard Ford Popular steering box. "To save weight we cast our own magnesium housing and machined it to accept the internals from the Standard Eight rack-and-pinion gear made by Alford and Alder. The housing was pivoted from the chassis at one end, with the single-ended rack connected to the central steering arm system that dated back to the Mark VI. It was lighter and fitted in better."

Although XPE 6 was fitted with Girling disc brakes from the outset and they later became a standard factory fitment on top-spec IXs, Lotus had developed its own highly effective drum brakes, mounted inboard at the rear to reduce unsprung mass. 'We'd had problems with front brake cooling on the VIII because it had narrow Alfin drums, so we developed wider cast magnesium ones with cast-in steel liners. They were very good brakes. The idea of the radial fins was to centrifuge air from the centre and fling it toward the outside to take heat away."

Chapman insisted that the IX be more than a foot shorter than the VIII because he wanted it to fit in his new transporter, which was intended to carry two cars. "Really, somebody should write a book on Chapman's transporters — the early ones, before he put thousands of John Player's money into them. Somehow he did a deal and got a Commer chassis and had a dreadful box built on it. He skimmed it right down to the last inch and it had benches that were supposed to carry one car above another. It never worked — we never took two cars in it."