Smaller spare, bigger space

FEW things can deflate a motorist’s mood like, well, a flat tyre. Fortunately, punctures don’t happen frequently these days, thanks to improvements in tyre technology and roads. (I’ve had just two in the past 10 years, the last one over four years ago.)

When it comes to shopping for a new car, consider the factors that Malaysians deem important – style, price, resale value, prestige, fuel economy, colour, comfort, safety, low maintenance, etc. But do you know of anyone choosing a car because it has a great spare tyre?

Danger

That may change if the Consumer Association of Penang (CAP) has its way. On Thursday its president, S.M. Mohamed Idris, claimed that the temporary use spare tyres that many cars are equipped with today pose a danger if they were not used in accordance with the car manufacturers’ instructions.

He has a point. Temporary use spare tyres and wheels are narrower and lighter than the other four standard wheels and tyres. So, they are not as strong, nor are they as good in all the other areas that tyres are expected to be good in, including grip and resistance to damage from road hazards.

There are two types of space-saver tyres – full size temporary spares that are narrower but have the same height as the standard tyres, and compact temporary spares that are not only narrower but smaller in diameter as well.

The latter pose an additional risk because a car will end up having one tyre smaller than the other three, which could affect stability.

Most European and many Japanese cars now come with space-savers while the popular local cars that use them include the Proton Waja and Savvy and Perodua's Myvi.

So, why would safety conscious carmakers specify such wheels if they are potentially dangerous?

More space, less waste
The primary aim of space-savers is to maximise space and minimise weight, the latter being a significant factor in reducing fuel consumption.

In coming up with specifications, the challenge that car designers face is to find the optimum balance between space that is usable every day and fuel economy that is beneficial every minute that the vehicle is running – and a spare tyre that is likely to be needed only once or twice in several years.

“The benefit that space-saver tyres bring is that they provide greater luggage capacity and improve flexibility of the interior space of vehicles,” says Ford Malaysia managing director Michael Pease.

“Space-saver tires have been used and approved by many (car) manufacturers globally for more than a decade now. When these tyres are used in accordance with manufacturer's specification, they have been demonstrated to be reliable and dependable.”
The key point is “used in accordance with manufacturer’s specification.”

Alternatives

There are other solutions to the perennial problem of punctures.
BMW, for example, has decided that the spare tyre is obsolete and is working towards offering cars fitted only with extended mobility or “run-flat” tyres that can be driven on even when punctured. Some other manufacturers offer these tyres as options.

When engineers invest so much time, effort and money to shave “mere grammes” from hundreds of components, it is absurd to lug around 20kg or so of spare tyre that’s rarely needed, according to BMW Group Malaysia managing director Wolfgang Schlimme.
Run-flats sound like the ideal way to go but they have limitations, too. They can be used only on cars equipped with an onboard tyre pressure monitoring system (otherwise, the driver may not be aware when a tyre is punctured).

While BMW insists that its suspension systems are tuned for run-flats, many drivers still feel that standard tyres offer a more comfortable ride.

There are also constraints on how fast and far run-flats can run without air, and the ultimate put-off may be that they cost 50-100% more than comparable conventional tyres.

Another option is some kind of temporary repair or sealing system, and inflation using either an electrically operated pump or compressed air and sealant stored in canisters.

These, too, have disadvantages; the tyre can be too severely damaged to re-inflate, or a simple valve failure can leave you stranded. The canisters have a finite lifespan, too.

The best may be the run-flat but, as with all good things, it comes at a price that many can’t or won’t pay. The cheapest in the long run is probably the space-saver, used appropriately and checked regularly.