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Colin Chapman had been uncharacteristically cautious, possibly more for financial than technical reasons, about embarking on rear engined cars. Cooper had taken one World Championship and were busy taking another before a "proper" F1 with the engine behind the driver instead of in front emerged from Cheshunt, the then Lotus base and H.Q. in 1960.
It was the "18" destined for a triple life with a variety of engines. One was the 2.5-litre, four-cylinder, Climax engine. When that was consigned to the dustbin by an international ruling that imposed, amid British uproar and general frenzy, a 1.5-litre limit in F1, the 18 got the four-cylinder Climax FPF. Chapman had hoped for a new V8 that was in the pipeline but not ready. The business success of the "18" was by no means hindered by selling it as a highly successful 1100cc formula junior car too.
The 18 achieved a sort of immortality with Stirling Moss's classic Monaco Grand Prix win, not only because it beat everyone from Ferrari down, an experience Britain had only just begun to savour, but because of Moss's decision to run for the sake of coolness with side panels removed: memorably revealing his legs, or the tubes of the classical spaceframe, depending on your sphere of interest.
Refined, lowered, smoothed and wider-tyred the 18 became the still spaceframed 20, then 21 and 24. Along the way, the Triumph Herald front upright - surely the most successful production car component ever pinched for racing - finally said one of its numerous farewells so that Chapman could not only choose his own suspension pick-ups, having gone inboard with the damper coil units but also move the rack and pinion steering up into perfect line with the top wishbone.
Climax's V8 had arrived and built up a reasonable, if erratic, record of wins in full GPs within two years. Reasonable that is for some teams. It was not a level of achievement that recommended itself to ACBC whose intertwined initials sat on the front of the cars, win or lose.
1962 brought an extraordinary mixture of events. The still potent 21 enabled Trevor Taylor and Jim Clark to take a quick first, second and fastest lap for openers in South Africa. A load of happy customers paid up for their brand new 24 spaceframe cars (not least being Jack Brabham and the Rob Walker Racing Team who were fielding Stirling Moss).
Then from the Team Lotus transporter at Zandvoort, in May, they saw the then un-buyable 25 monocoque emerge. There were only ever to be seven of them. Within sixteen months the perfectly integrated partnership of Jim Clark and Colin Chapman with the 25, created by one to be used with dominating perfection by the other, gave both car and driver their respective Championships of the World.
In fact it had been so good out of the box, that starting halfway through 1962, Clark only missed the Championship in its first season when a much publicised 4 inch bolt fell out of the distributor mounting, near the end of the final and key race, to be rapidly followed by all the engine's oil.
Everyone knows how it is done - afterwards. The boldness is in the workshop and drawing office, the thinking and the risk taking. The world is quite full of people with ideas, some of which are potentially excellent. Carrying them through is a different story.
Hollywood would have been proud of the 25's faintly novel-like beginnings, sketched in rough outline on a restaurant napkin. But Chapman had his misgivings, as he was later willing to publicly admit in Doug Nye's book, Theme Lotus: "Why not space the sides of a backbone far enough apart for the driver to sit between them. Made as box sections we could carry fuel inside in rubber bags. It was the first monocoque racing car, so far as I was concerned". (He was not unreasonably ignorant of the 1912 French version of this idea in laminated wood veneer).
"I'd never seen one before and we didn't know if it would work. We sold the spaceframe to our customers. We could not sell them a revolutionary car which might not work at all and might need a long and expensive development programme. At that time it was really an unknown animal".
As it turned out, it must have had one of the shortest development programmes ever for a totally successful car, but who is counting the days? Certainly it was still being cut and riveted, its bulkheads fabricated, and suspension borrowed from the 24 a long time after Christmas 1961.
Twenty years later it was only just giving way to what the 25 itself was often called but was not - the "bathtub" car. This latter came about with the neat, tall, narrow hipbath-shaped structure of the glued honeycomb, true venturi, cars in the very late seventies.
Until this was both forced and made possible by side pods and new materials, it is instructive to see how much of the 25 conception was so right from the word go that it became the pattern for every F1 to follow. While the Brabham BT26 was determinedly soldiering on - very successfully - with tubes seven years later, it was the farewell flourish of a bravely dying man.
Imagine if you will, in a world totally dominated by and dedicated to the tubular spaceframe, a cardboard tube a couple of inches in diameter and eight or nine inches long. Bending or twisting it with your bare hands verges on the impossible. Lay another parallel to it three inches away.
The difficulty is not to make them stiff, but to join them in such a way they are held rigidly parallel to each other, no easy matter. The methods conceived for the 25 were virtually those of everyone since. Two vital bulkheads, one behind the driver and one beyond his feet, link the two tubes, together with a marginally less rigid one at instrument panel level. Our two side tubes have become flattened into D sections, to permit economic insertion of the driver between them while keeping everything as narrow as possible.
Those flat inner surfaces, together with the floor linking the two are now tied together with panels that begin behind the driver's neck, support his reclining back. then posterior and rising thighs, to his knees, falling again towards his heels. These zig-zagging surfaces, provide on their way triangular boxes into which can be usefully inserted another fuel tank, fire extinguisher bottle, battery or other electrics.
The two sections of pontoon left projecting rearwards into thin air beyond the bulkhead separating driver and engine are then tied together by a power unit, bolted in solid, making it all one integrated structure. The final small bonus is that beyond the driver's feet a totally rigid subframe can be made, not only carrying the front suspension but giving a portion of its own strength to keeping those original two tubes accurately and rigidly alongside each other.
Really the only major change in the monocoque's history since then was that the Cosworth DFV when it arrived had been conceived from the very beginning as half the car, 4-bolted to the engine bulkhead at its front, and carrying suspension links damper/coil units, rollbars, wings, gearchange and assorted other bric-a-brac all by itself at the rear end.
Chapman had always been a man inclined to controlling, as closely as possible, exactly what the wheels and tyres of his racing cars were doing by carefully planned suspension geometry allied to soft springs with stiff dampers adjustable in both bump and rebound. The success of such an approach is founded on the pickup points for the suspension staying where they are supposed to be, dependent in their turn totally on the torsional stiffness of the chassis.
The monocoque rocketed the torsional stiffness figures by some 200 per cent, and saved ten or fifteen pounds of weight into the bargain. As this happened to be the twilight of the fifteen inch diameter "bicycle wheels" and narrow tyres, control of wheel angles through the suspension was shortly to become ever more important.
The internal dimensions of the car were so closely controlled it would have been practically impossible to get taller or fatter drivers than the modestly proportioned Clark and Taylor into the cockpits at all.
Beside their lie-down seats the gearchange, travelling through tubes let into the monocoque sides, had a lever operable by hardly more than rotating the right arm to allow a couple of fingers to move it in a tiny gate. Space was so limited Jim Clark once said he had to allow himself time somewhere in every lap to drive with one hand while he flexed his gearchange arm to avoid cramp.
Astonishingly there were still quite a number of rubber bushes in the suspension but these did not last long and were gone by the Championship year of 1963 - as were carburettors in favour of fuel-injection.
Other development thinned the L72 alloy sheet of which the car was largely built by a couple of gauges, improved the cooling and altered the geometry. Further, the victorious year of 1963 was used - apart from winning the Belgian, Dutch, French, British, Italian, Mexican and South African Grands Prix - for a succession of experiments on thirteen inch wheels, totally different tyres and suspension geometry and location - all for the coming 33.
Though nearly all the 25s created were either wrecked or ended in the hands of private collectors you can still go and study R7, the last one, and ponder its technicalities, in Tom Wheatcroft's incomparable museum at Donington.
There could be few better ways to spend a quiet hour.
This text is a chapter in the enjoyable, informative and helpful book by Allan Staniforth.
Race & Rally car source book : a D.I.Y. guide to building or modifying a race or rally car / Allan Staniforth. - 1st ed. 1983; rev. ed. 1986. - A Foulis Motoring Book; Sparkford, England: Haynes, 1987. - 204 p. : ill. ; 28 cm
Topics covered: springs (steel & rubber); Dampers; Anti-roll bars; Rising rate suspension; Suspension geometry; Setting-up; String computer; Steering; Rack & pinion units; Bump-steer; Tyres; Wheels; Fabricating wishbones & steering links; Rollcages; Fuel tanks; Brakes; Glass-fibre; Carbon-fibre; Costing; Gear ratios; Ground effect; Wings; and whatnot.
With Richard Blackmore, Allan Staniforth designed the Terrapin cars and took six British and three international speed records with the supercharged version of his first hillclimb car - three of which records are still held when above book was published in 1987.