Why Is Coast Down Testing So Important?

A few years ago I had an illuminating chat with an engineer from a UK-based manufacturer (they make very nice cars, that’s all I can say about who he worked for) who described their coast down practices. One thing I learned was that going somewhere hot, like Arizona, nets better results than they could ever hope for if they did it in the UK – for one thing the consistency in temperature makes life easier. Plus they like going to Arizona.

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I was reminded again recently about the importance of coast down testing. We’ve been selling VBOXs to the industry for years specifically for this purpose, but recent conversations with the guys at the sharp end have made me realise just what a big deal it is.

Why is it so important? It’s those emissions regs again (for which the EC type approval document is… long). For the manufacturers, making cars with low emissions values is vital these days – not just from a legislative, but also from a sales and marketing perspective.

Official emissions testing is carried out on a dyno where there is no wind resistance. To compensate, an extra load is placed on the engine via the dyno’s rollers – the amount of which is derived from the coast down results previously generated at the test facility. No wonder they want to get these numbers in a conducive environment.

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The coast down values must have a statistical accuracy that falls within a 2% range, so consistency is essential. We supply specific software to abide by the regulations laid out in EC70/220 and it’s good to know that wherever they’re testing, the engineers can rely on it.

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