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www.engineeringnews.co.nz 21 the trailing arms, which can make the turn in unpredictable,” says Nelson. “The jury’s still out on whether it is a real benefit for a Sprint Car, but it could be useful on other forms of speedway car racing. The concept is quite good and early results are encouraging. You can have some really odd spring rates from the rear of the Sprint Car by virtue of the kinematics of the car and the way they lean into the turn.” The wheels are often massively offset with huge amounts of stagger. Anything from 8” to 16” inches difference in rolling circumference of the rear tyres from side to side. The wheels can be staggered as much as 300 or 400 mm depending on the track. “On a really heavy track, where there’s a lot of grip, the car will be staggered substantially, to discourage the tendency for the car to roll over,” says Nelson. “Unlike a circuit car, it’s very easy to roll a Sprint Car just by tipping it into a turn too aggressively.” The Sprint Car category hasn’t changed much in the last 20 years, unlike F1 or any other open wheel circuit racing category which has changed massively over the same period. “So our approach to building Sprint Cars is to try and inject some modern innovation, while still working within the rules,” says Nelson. “There is also a tendency to stick rigidly to the American traditions of Sprint Cars rather than to try and improve things for the better locally. The live front and rear axles are a case in point, this is really antiquated automotive engineering, especially since independent suspensions and active suspension control are standard on many domestic vehicles today.” In Sprint Cars it doesn’t matter whether you buy a Triple X, Maxim or J & J chassis the engine plate from one will fit on the others and things like the front torsion arms are interchangeable. “It’s not so much standardisation, as the fact that everybody copies everybody else,” says Nelson. “This sort of thing doesn’t happen in other formulas – you couldn’t put a Dallara upright on a Reynard for example.” The same kind of reliance on tradition has meant that some performance parts from the US are lagging behind other markets. “Parts from Europe or Japan are too expensive, so we make our own,” says Nelson. “Sometimes it’s difficult to get parts from the US, but in general the quality doesn’t meet our requirements. For things like oil pumps and fuel pumps and relatively standard components we would buy from America. But in terms of performance parts, they tend not to change the designs, so it’s much more costeffective to develop our own performance parts from scratch.” The other Sprint Car design departure is that Nelson has abandoned the traditional unstiffened birdcage and introduced significant cross bracing. He has eliminated the chrome moly frame in front of the driver and with custom-machined bulkheads, has made the engine a stressed part of the chassis as in an F1 car, but the other way round. He has also fabricated an aluminium glu-lam monocoque box section (à la Lotus Elise chassis) in front of the engine holding the front suspension and housing oil reservoirs for the dry sump. This has been developed in a ‘lighten it until it breaks’ manner as it’s virtually impossible to Image left: Unique 3 spring ‘coil over’ rear suspension. Semi-monocoque Sprint Car underneath the skin.


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