Should OEMs be more upfront about vehicle braking distances?

While tyre manufacturers do everything in their power to reduce braking distances, recent test results highlight that there is performance gap wider than a supersingle separating the best and worst braking systems on new vehicles. That's the conclusion of a recent report by the UK's leading consumer magazine Which? The consumer watchdog measured the average distance new cars took to stop from 62 mph, one of the ongoing tests Which? carries out across 160 cars a year. In the supermini category, the Volkswagen Polo took 34.16 metres to come to a stop, whereas a Suzuki Alto took 42.52 metres – a performance gap of over 8 metres.

The worst performing car in the test was an MPV – the Chrysler Grand Voyager at 43.49 metres. Others that didn’t fair well include the Mercedes A-class, bottom of the medium cars category at 41.61 metres, and the Land Rover Freelander, bottom of the 4×4 category at 42.04 metres.

For those of you interested in the methodology, in this test Which? fills the car to half load (with two adult passengers) and ensures tyre pressures are correct. Which? then performs an emergency stop test from 62mph to 0mph (100km per hour to 0km/h) and measures the stopping distance using a GPS-based Racelogic tracking computer – the same kit used by racing teams. The magazine repeats this emergency stop test 10 times in quick succession and the average of these 10 braking tests is the overall braking distance figure quoted for each car.

Peter Vicary-Smith, chief executive of Which? said: “Car manufacturers are good at telling us how quickly cars get from zero to 60 miles per hour, but they’re not so good at telling us how quickly they get from 60 to zero. We think people should have this information before deciding whether to buy a car. This could be a matter of life and death.”

But should OEMs be more upfront about vehicle braking distances? The Which? test gives brakes a real pounding, and is designed to highlight any tendency to fade – that is, where brake performance reduces as brake temperature increases. Any car that exhibits fade is marked down accordingly.

What the Which? Report is not clear about is the exact reason for the tested cars’ good or bad performance. Could the well-known consumer magazine’s automotive branch be passing comment unwittingly on the relative merits of the different tyres supplied to the tested cars as original equipment?

The tests also appear to overlook the fact that most mainstream vehicles split OE across more than one tyre supplier. This is significant because without conducting the tests in parallel with each of the different OE tyres no objective judgements can be made about the braking systems’ stopping power. What’s to say that one set of tyres couldn’t bring the same car with the same brakes to a standstill, metres shorter than another? True, OE tyre supplier are usually drawn from amongst close competitors that don’t generally have this much between them, but numerous magazine tyre tests prove that one tyre can often stop metres shorter than another. All of which makes you wonder whether car manufacturers could – on account of the fact that they may have to releases multiple sets of stopping data across each of their different fitments – or would even want to – because of the potentially bad press it could generate – publish vehicle stopping figures.

However, from a tyre industry point of view the Which? Story somewhat sticks in the craw; especially with the continuing legislative drive putting legal pressure on tyre makers to do what the perpetually do anyway – strive to reduce stopping distances with every new product. Stripping the story down to the bare facts, what it’s really saying is: lower performing brakes can cancel out the positives offered by tyres with strong braking characteristics.

What do you think? Email theeditor@77.237.250.82 to air your views on this or any other issue relating to the tyre and wheel business