The Spare Tire

Temporary Spare TireHave you checked your vehicle's spare tire recently? Depending on your vehicle you may have a full size spare, a temporary spare or no spare at all. Knowing what to expect in the event of a flat tire will mean avoiding inconvenience or being stranded at the roadside.

Full Size Spare Tire

If your vehicle comes equipped with a full size spare tire you well prepared to look after a tire failure. The usual drawback here is having forgotten to check the pressure regularly and finding it low or flat itself.

Knowing where to find and how to use the jack and tools before a flat occurs is a good practice as well.

Temporary Spare Tire

One cannot use it to replace a flat tire and carry on as normal. The owner's manual for my vehicle says "The compact spare is for temporary emergency use...the original tire should be repaired (or replaced) and reinstalled at the first opportunity."

It goes on to specify the correct inflation pressure for the tire and a maximum speed limit of 80 km/h when using it. It also warns about reduced ground clearance and cautions that the driver must be aware of this.

The Motor Vehicle Act Regulations reinforce the importance of using this spare tire as little as possible. They allow the use of the temporary spare only if the driver makes arrangements immediately to repair or replace the original tire.

Drivers who neglect to deal with the situation immediately may be subject to a fine and the possibility of having their vehicle removed from the highway until such time as an adequate tire has been installed in place of the temporary spare.

No Spare Tire

Many vehicles today come without a spare tire of any kind. Manufacturers have omitted the spare, jack and tools in order to save weight and improve the model's fuel consumption ratings. This leaves you at the mercy of roadside assistance services unless you are prepared to help yourself.

Having run flat tires on your vehicles are an option, but they do tend to be more expensive and offer a rougher ride.

You may choose to carry a full size spare and the necessary tools either full time or just when you are taking a longer trip. Tire sealants and a compact compressor are also an option if the tire damage is a simple puncture.

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As I used to manage a fleet of driving school cars, one thing that became apparent was that the 'spacesaver' spares are typically mounted in the trunk with the tire valve situated on the 'other side'. And spares, just like mounted tires, lose pressure over time. So even if you pay your dealership or tire shop lots of money to properly maintain your vehicle, it's worth asking whether they took the time to unsecure it from the trunk, and verify that the pressure was at least up to the maximum recommended. Don't be surprised if nobody has checked it since the car was manufactured; dealerships in particular tend to extol what they have done, without bothering to mention what they ignored.

Separately, with regard to my own vehicle - a 2012 Ford Econoline LWB - the spare Hankook doesn't appear to have ever been used (though I have ensured that the pressure is always maintained at or slightly more than the minimum pressure). But after more than a decade since manufacture, and despite being kept out of direct sunlight, can it actually be relied on, if needed?

Having already taken this thread a bit off topic (as now I'm refering to commercial vehicles), and as I know our site host is a 'tire guy', I found it interesting to note recently that while the Econoline solution to potential loading is to specify 55 psi front / 80 psi rear (yeah it does bounce around a bit when empty), the modern Transit successor uses dual rear tires with a reduced aspect ratio, and the recommended pressure is 67 psi front, 57 psi rear). 

It's definitely recommended that vehicle owners check their pressures this time of year, simply because - even if there has been zero leakage - the tires will have lost pressure due to the ambient temperature. 

Meanwhile, I am of the strong belief that passenger car tire pressure recommendations are usally too low, mostly to maintain a 'soft' ride. It's common to see a sticker on the driver door jamb that will ask for 32 psi, whilst the maximum pressure specified by the tire manufacturer is 44 psi. Quite a difference! In this case, splitting the difference (i.e. 38 psi) will in no way adversely effect the integrity of the tire, or its longevity / wear across the tread; but it will improve ride, and handling, and fuel mileage. Your results may vary. 

I do take some exception to the supposition that the engineers that designed the car might not know the best tyre pressure for your car (but it is a compromise) or that running 15% higher pressure won't have adverse effects.

Running higher pressures is more likely to adversely affect ride, rather than improving it.

Higher pressures can also change tyre profile, causing tyres to wear faster in the centre.

Higher pressure can also affect the ability of the tyre to get up to proper operating temperature, which may affect handling.

That being said, it's probably better than running 15% too low (unless you are racing)