Under the skin of Jim Clark's Lotus 29

Revenge was exacted in various ways. Jim Clark – whose one previous drive at Indy was a test session in a 25, an experience he described afterwards as “a bit dull really” despite a best lap of 143mph was compelled to take a humiliating rookie test. In the race itself Gurney started well but slipped back to seventh at the finish, whereas Clark, despite being robbed by yellow flags of much of the advantage of his fewer pitstops, looked set to win until Parnelli Jones’s leading roadster infamously began to leak oil onto the track. Furious complaints by Chapman failed to get Jones disqualified and Clark had to settle for second. A prize purse of over $55,000 helped soothe Lotus indignation. As did an emphatic win in the following Milwaukee race, where Clark led for all 200 miles.

Len Terry would exact his revenge in turn in 1965, when Clark triumphed in the third-generation Lotus Indy car, the 38, to become the first non-American to win the race since 1916. Still, that 1963 ‘robbery’ irks even today. “If they had stuck to their own rules we would have won the race,” says Terry for what must be the umpteenth time, “but I’m biased, of course.”

Construction of the 29 was on the ‘bathtub’ principle first used in the 25. To maximise its fuel capacity and so capitalise on the decision to use pump fuel, the chassis ‘sills’ were taller and wider and a saddle tank was added above the driver’s legs, bringing the total capacity, including the small tank behind the driver’s back, to an impressive 42 gallons. Unlike the 25, the tanks were interconnected using a system of non-return valves of Terry’s devising which allowed fuel to flow into the left-hand sill tank but not out of it — other than to the engine! — thereby ensuring that the weight of the fuel load remained evenly distributed through lndy’s succession of left-hand corners.

Ford’s pushrod Fairlane V8 must have seemed pretty crude to Lotus eyes compared to the Coventry-Climax FWMV used in the 25, and its 370bhp from 4195cc (just 88bhp/litre) compared very poorly with the 130bhp/litre achieved by the Coventry unit the same year.

One consequence was the unexpected kink in the front tube of the lower wishbone, which required an extra tube to be added to triangulate it — a distinctly un-Lotus feature. On the right side of the car this arrangement appears perverse, but the reason for it becomes obvious on the opposite side. Here the inboard pivot of the lower link has to be located further inboard to accommodate the body’s offset, with the result that the wishbone would foul the rear bulkhead hoop if it didn’t incorporate that kink.

A Colotti Type 37 transaxle replaced the ZF unit used in the 25 to accommodate the much higher engine torque. Only two of the four available ratios i were used — one low enough to start the car from a standstill and the other for normal lappery.

The 25’s inner Metalastik ‘doughnut’ UJs, which would have wilted under the Fairlane’s torque, were replaced by a Hooke joint-and-roller spline assembly, supplied by American firm Saginaw. Terry recalls that the driveshafts may have been derived from truck units, which would explain why they look so unfeasibly large for a racing car.

Offsetting the 29’s body 2.625in to the left was done principally to even up tyre wear — essential if the 29 was to run fewer pitstops. Originally the car was fitted with Dunlop rims, but when Firestone agreed to manufacture 15-inch tyres for the Lotus, it understandably wasn’t too happy at the prospect of these being carried on a competitor’s wheels. So Lotus substituted American-made Halibrand knock-off rims. Ironically, Lotus switched, against Ford’s advice, to Dunlops for the Type 34 in 1964, only for tyre failure to bring the Lotus-Ford challenge of that year to a premature and ignominious end.

Despite the high average speeds on US ovals the braking requirements were relatively light so, although provision was made for increasing the disc diameter if necessary, the 29 ran with precisely the same 10.5in Girling discs and calipers used on the 25 in Formula One