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A petrolhead's lament: What happened to 'power-to-weight' ratios?

2016-05-05 12:11

Calvin Fisher, TopCar

WONDER, WONDER: TopCar's Calvin Fisher ponders about the good old ‘power-to-weight’ ratio. Image: iStock

Cape Town - Whatever happened to the good old ‘power-to-weight’ ratio? Easy to decipher and honest in its verdict, it’s as stalwart a measure of a vehicle’s athletic prowess as the quarter-mile dice and zero to hundred sprint.

Real ‘top trump’ stuff, emerging from a capable science of predicting a car’s performance and dynamic characteristics, all with a simple ratio that sets engine output against kerb weight.

Yet that hardy ratio has been all but relegated to measuring the carbon composite-rich supercar elite.

Ratios for everything

It’s of shrinking worth when bellied up against some of the new, greener staples of the industry – the likes of ‘litres per 100km’ and ‘grams of carbon dioxide per kilometre’. Purer and purer fuel is required to make the most of the clever new engines being built to meet the new imperatives, but that’s okay because we even have ratios for that. Sulphur content? 50 parts per million is good. 500ppm must try harder!

Just listen to the mental environmentalists whine in unison between their sips of herbal tea about how evil the automobile is and how it should be improved if not culled, all in the name of efficiency. How ironic, as the quest for optimum power to weight has exactly the same outcome. What the Earth really needs, I say, is a return to the old ways of thinking.

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In pursuit of a purer driving experience, Lamborghini gave us the ‘Sesto Elemento’ concept, literally ‘Sixth Element’ – a reference to carbon – from which it has largely been constructed. It’s the anorexic twin to the Italian firm’s Gallardo, but thanks to extensive usage of the light-but-strong weave, it weighs in at just 999kg.

That’s 50 kilos less than a Ford Fiesta despite mechanical necessities such as a 10-cylinder engine, E-Gear transmission and drive to all four wheels. And to do this, Sant’Agata’s best consulted with the boffins at Boeing, long-time specialists in the dark matter. Gone is the old supercar ethos of lashings of power and overwhelming visuals. Instead technicians at McLaren, Ferrari and the like have traded flowing pen lines and aggressive vents for extensive aero testing. Will the slipperier shapes styled by science give us cars that look like aeroplanes, which, ironically enough, are among the worst green offenders?

Mercifully, and thanks to Formula 1, with more than a nod to Colin Chapman and his ‘Simplify, and add lightness’ mantra, we still have cars that shock and awe, supplemented by clever tech that justifies a green conscience. 

Power-to-weight yardstick

Good too that the new science has embraced carbon (adding lightness) for more than concepts, and it’s filtering to the mainstream if BMW’s all-electric Megacity Vehicle (MCV) is any indication. I’m not saying the dark stuff is the answer, just that a low kerb  weight is paramount in saving the world. That said, if in the future I see a ‘Joy is E-fficiency’ poster, I’ll bloody well eat it.

Still, we at Topcar are real-world drivers with sports days and band recitals to consider, so if the power-to-weight yardstick is now truly obsolete, rather than throw up our hands in frustration we’re embracing the quest for a new unit with which to measure the abilities of the latest vehicles filling up our driveways. How about a ‘doors-to-cylinder’ ratio?

The Subaru WRX STI sedan seems to generate a modest 1:1 ratio as it boasts four of each, but that offers up absolutely no clue to the fiery performance it delivers, compared, say, to the Suzuki Alto which boasts the same ratio. Perhaps ‘seats to boot capacity’ will do the trick, but single-cab bakkies might take honours over a Pagani and that doesn’t feel quite right either.

'Understand our fears'

What if I need a big capacity engine with forced induction to drive the sheer bulk of my SAV, in the Q7, X5 and Cayenne tradition, where the more cylinders the merrier applies? Disturbingly, it’s the (high) kilowatt to (low) carbon emissions ratio that will be the most logical measurement of worth to those pesky e-mentalists, ignoring the practicality on offer in a vehicle that can ferry seven occupants at a time.

Can you understand our fears as engines shrink? Do you too lament the dismal world that awaits the petrolhead if our cars cannot shed their weight?

Perhaps when all is said and done, it’s a combination of existing formulas that will solve our conundrum.

Could ‘power divided by weight, multiplied by CO2 over litres per 100km’ be the formula that saves the day? Or at least have us clamouring for the nearest hybrid, heaven help us. Until then may the world continue as is, because while great cars are often efficient, efficient cars are seldom great.

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