Bad news for supporters of ‘loud pipes save lives’. They don’t do any such thing, and for the simplest reason of all: car drivers can’t hear even loud motorcycles.

Having demonstrated some time back that even brightly coloured and exotic-looking bikes – in my case an almost fluorescent Benelli 1130 Tornado Tre – don’t get through to drivers, this is not welcome news. A potplant in a Volvo (old Australian expression for gormless drivers) moved into my lane and almost punched me into the side of a bus. What’s left?

It could be argued that loud pipes are as American as Route 66! And perhaps just as superseded.

Interestingly enough, in that particular case loud pipes might have helped – see below. But let’s start from the beginning.

We all know that motorcycles are far too often overlooked in traffic. True, though sad. We also know that noisy pipes alert drivers to our presence. Even more sadly, not true. Don’t believe me? I have proof, albeit from Romania.

The Romanian Pro-Motorcycle Association for the National Development of Motorcycling, together with the Polytechnic University of Bucharest and the noise emission specialist Enviro Consult, has conducted a study to determine how much of the motorcycle noise actually reaches the car.

Specifically, the question they wanted answered was where and when the motorcycle becomes audible in the passenger compartment. They found it difficult to measure this while driving with any scientific accuracy, so the research group conducted the tests while the car was stationary – but with the motorcycle at maximum revs.

At the same time, the car’s engine was kept between 2,500 and 3,000 revs and the radio was set to 20 decibels, a volume considered normal. The motorcycle was then placed first 15 metres behind the car, then ten metres, then next to the car and finally in front of the car.

So what we (or rather the Romanians) have here is a stationary noise measurement much like the one used by police, only at maximum motorcycle engine speed with a correspondingly extremely high sound pressure. Sound pressure is the aggregate of all frequencies.

Benelli appears to have given up on being seen, and has become more discreet.

If you think that the sound of a motorcycle howling on the rev limiter only 15 metres behind a car would make the driver snap his head around, you are sadly mistaken. The motorcycle is simply not audible at 15 metres behind the car, which is the minimum distance between vehicles recommended in urban areas. Things are no better at a distance of ten metres. The combination of the sound insulation of the car and the sound pressure of the frequencies it generates itself, including that 20 dB radio, is greater than the noise of the motorcycle.

Below this distance, the motorcycle slowly becomes audible in the car. But here’s the rub: that is only in terms of sound pressure, the total of all frequencies. It does not mean that the driver can pick the sound of the motorcycle out of the noise that reaches him. This is a particular problem because even then, only very low frequencies arrive in the interior and these are not only more difficult for the human ear to identify but also even more difficult to isolate among other frequencies.

Finally, with the front wheel of the motorcycle level with the rear wheel of the car, the sound pressure of the motorcycle becomes clearly audible in the car for the first time. Only the loudest of the six bikes tested could be heard, however, and its exhaust put out 110 decibels. So even when they were moving up level with the car, the other five motorcycles are still far below the audible limit.

In other words, the average motorcycle will only really become audible in the interior of the car when it is level with it. By then it is pretty much too late to abort a lane change or any other move on the part of the driver. So the window in which loud pipes might be considered to save lives is quite small.

Is motorcycle noise a matter of freedom?

Here is some background to the study. The difference between the loudest and quietest motorcycles tested at maximum revs was just under 30 decibels, in other words the perceived difference in loudness was some ten times.

On average, the difference in sound pressure in front of and behind the motorcycle was measured at seven decibels. Behind the motorcycle, then, the noise is perceived as more than twice as loud as in front of the motorcycle. That’s a problem when you want drivers in front of you to be aware of your presence – and presumably not annoy the drivers behind you too much.

Although that problem might not be too bad because the sound pressure inside the car decreases again when compared to the measurement next to the car. Cars are apparently designed to be as soundproof as possible from the front.

This is not good. But all is not lost. My own research, conducted intermittently over several decades, suggests that there are auditory and visual cues that work to keep riders safe on the road. Unfortunately these include not only aggressively loud pipes but also a scratched flat black half-helmet, tight-fitting shades over a grey beard (a long one on the blokes), colours worn over scuffed leather jackets and stained jeans.

And remind me not to buy any used bikes from Romania.

Photos of or by The Bear)

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