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A PHYSICIST WRITES . . .

(February 2014)

Which items in a car are critical for your safety? Tyres and brakes, certainly. And after these, the lighting, I would say. If I notice a vehicle with a rear light or brake light out of action, I feel that I must take any safe opportunity to tell the driver. Incredibly, sometimes you even see two brake lights missing, out of three: how many months since they were checked? And why hasnít anyone else done the decent thing (and also the self-preserving thing, if you want a clear warning that the car in front is braking) and let the driver know that he or she is two lights down, with one to go (after which you will get no warning at all)? As for driving with a failed headlight, the excuse for this canít be that I wasnít aware of it, officer. It must be that the garage is booked up solid for another fortnight, sorry.

Is it only me who feels real alarm at seeing a car with a headlight out, and even more so if the sidelight has gone as well (which is often the case)? At night, you could easily glance at such a car, think itís a motorbike and make a serious error in aiming to pass it by. And with the driver being so carefree about being visible, what else might he be careless of? Anyway, hereís a suggestion: if your repair-shop is going to have to replace a bulb for you, ask them to change the opposite one as well (as itís probably wonít be long otherwise before this burns out too) Ė saving you time, money and another period in peril.

Well, you can imagine how relieved I was, last year, to find that my new (2010 registered) VW Golf possessed not only a dashboard warning-light to indicate any dead bulb, but also (in spite of its recent date of manufacture) bulbs that I could replace myself! Yes, I checked each different one. But you may be able to guess what happened in the next episode of the story. I thought: this Golfís a popular modern motor, should be easy to get a set of spare bulbs specifically for it. How wrong I was. Even the VW dealer in Reading offered me only a general set containing a random selection of bulbs.

Of course by then I knew exactly the nine types that I needed, and I wasnít going to let the hunt for them defeat me. I found them variously at Halfords, at VW again, at a Motorists Discount Centre and on Amazon, where I finally tracked down the unusual silvered front-indicator bulb, strangely described as a BMW Genuine Headlight Bulb (though definitely the right one for me, from its look and its part number) and painfully priced at £21. It occurs to me now that Amazon could probably have supplied all nine bulbs, if I had looked there first.

I guess the manufacturers are to blame for this chaos by not standardizing, or rather, not continuing with the system of a few standard bulbs that Iím sure existed years ago (even if the actual list of bulbs might have needed to be updated since). And what a nonsense it makes of the legal requirement, as stated on countless travel websites, that a complete set of spare bulbs must be carried when driving in Spain.

Of course, itís a good idea to try to gather them together for driving anywhere Ė but really, is a policŪa ever going to stop you and check (somehow) that they are all present and correct? And even given that they are all there, if a bulb then blows and you replace it on the spot, you will have an incomplete and hence illegal spare set. To avoid this situation, you had better stock up with two of ... wait a minute: Iíve just come across an RAC webpage, dated last August, advising that it is no longer compulsory to carry spare bulbs in Spain. Iíll leave this confliction with you.

If I switch topics now to fuel consumption, please donít ask how the Golf compares with my old Corolla, for miles per gallon: Iíve no idea! I never looked up the Ďofficialí figures for consumption, nor have I tried to measure it. My reasoning is that mpg varies greatly from one minute to the next, depending on the road and how Iím driving along it, and so any useful number for comparison purposes would need to be an average, worked out over a long journey (or over a year) that I could exactly repeat, which I couldnít.

And who buys their fuel by the gallon anyway? But all this is just my view of consumption figures. Iím sure many drivers are comfortable with mpg, and understand how to compare the numbers ... but forgive me if I just test this last notion on you: letís say (purely hypothetically) that my Corolla averaged 46 mpg, and that the Golf is an improvement at 60 mpg. And suppose that you too have changed cars, from a gas-guzzler that only achieved 21 mpg, to one that does rather better at 25 mpg. Assuming we cover the same annual mileage, which of us will save more money in petrol with their new vehicle, you or me?

So that you donít read straight on to the answer, I will mention here that while writing this column I have been thinking that something is missing from its first couple of lines. And Iíve just now realized what Ė the driver! How can anything be more safety-critical than the ability of the person at the wheel?

Back to consumption: if I tell you that one of us saves 50% more in fuel than the other (by changing cars), does this help you decide who it is? Surely my big jump in mpg far outweighs your small one? No: your annual bill drops by many more pounds than mine. One reason is that yours is more than twice as big to start with. But what makes the answer so unintuitive is that consumption was stated in miles per gallon, when it should logically be gallons per mile. Or better still, litres per 100 miles (lphm, Iíll call it). Let me convert the numbers in the second paragraph above, for you: my consumption improved from 9.9 to 7.6 lphm, yours from 21.7 to 18.2 lphm. Itís not hard to see now that you will be saving more litres than me (over any given distance).

Did you read the story last year about the Italian who drove his silver Golf to Munich for the Oktoberfest? I felt such sympathy for him: he parked in a side-street, but forgot where. He searched for five weeks on and off, visiting by train in order to tour the city by tram, until the car was noticed by a resident who had seen his desperate advertisement in a local paper. Hereís the problem, then: how to make a Golf stand out, whether its colour is light (like the Italianís) or dark (like mine)? I fear the only sensible answer is to paint contrasting stripes on the roof...

Peter Soul

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