Spare Wheels And Tyre Repair Kits
(18 October 2012)
Bit of a tizz going on at the moment on the subject of spare wheels. In one corner we have the BBC's Watchdog team swinging through the trees to speak up for motorists inconvenienced for want of a spare, in the other the Society of Motor Manufacturer and Traders defending, as its name shows it must, the current state of the industry.
Although I'm not a big fan of Watchdog when it comes to motoring issues (it made an unholy arse of an inquiry into fuel economy figures several years ago, for example), I have to say I'm on the BBC's side here, as I shall now demonstrate by temporarily appearing not to be.
A spare wheel is in some ways a villainous thing. For most, and in some case all, of the life of the car it's fitted to, it serves no purpose whatever, because let's face it, why do you need a spare when you don't have a puncture? And as well as doing the square root of bugger all for years on end, it takes up space that might be required for other purposes and adds weight to the vehicle.
Owners generally like to have as much space as can be provided, so it's tempting for a manufacturer to ditch the spare so that more of it can be provided. Doing the same thing to reduce weight has even more appeal, because a lighter car will, all other things being equal, be faster and handle better and brake more efficiently and use less fuel and emit less CO2 and, because of the CO2 thing, cost less to tax than a heavier one, and who wouldn't want all those things?
Hence the appeal of the space-saver wheel, which in its early days was primarily intended - anyone? - yes, that's right, to save space, but is now worth considering for all those other reasons too.
From this viewpoint, tyre repair kits, which replace spare wheels altogether, are better still. They use a clever sort of foam which, when squirted into a punctured tyre, both inflates it and seals the hole. They also take up very little space and don't weigh very much at all. Game, set and match to the tyre repair kit.
Except not really. In terms of usefulness in the event of a puncture, tyre repair kits are much nearer the chocolate teapot end of the spectrum than a proper, full-sized spare wheel is, as the following not-to-scale diagram shows.
Space-savers aren't actually too bad, and would unquestionably appear to the left of kitten videos on the spectrum, but you can't use them for very long and, being much thinner than the other tyres on the car, they create a dynamic compromise which means you have to be very careful when driving on one. With a tyre repair kit, the chances of you being able to continue driving at all are very limited.
There's no problem if what has caused a puncture is a small hole in the tread, but that may not always be the case. If the hole is large, the foam won't be able to deal with it. If the hole is in the sidewall, forget it. If the wheel is damaged, forget it.
I've had to use repair kits in two pothole-related incidents, and they didn't work on either occasion. The first time, the wheel was buckled, and there isn't a foam in the world that will fix that. The second time, the tyre was distorted beyond repair. Both times, I had no option but to drive home (fortunately not very far) on mangled rubber which I couldn't replace because the assumption was that with a repair kit I wouldn't need to.
My worst encounter with a pothole was so severe that the wheel that hit it actually snapped in two. (I was only doing 50mph. It was a very deep hole.) This was after midnight, in the rain, five miles from the nearest habitation, and it's just as well that the car I was driving had a space-saver. I don't even want to think about what would have happened if it had been fitted with a repair kit instead.
And how about the habit some manufacturers have of providing nothing but a repair kit, or even a space-saver, in an off-road vehicle? If a tyre fails while you're in a river and have no way of getting out except by driving up a thirty-foot muddy slope, how exactly are you going to bring your SUV home?
So, while I can see why a culture of avoidance has built up on the subject of full-sized spare wheels, they are clearly the only sensible things to have if you're in the unfortunate position of having to deal with a puncture. When I'm in charge, they will be made compulsory, and the engineers can deal with the resulting space and weight. They won't mind. They enjoy that kind of thing really.
