By Shell on Feb. 29, 2020
There are also those that split the difference with something that isn’t a ‘true’ spare but will get you through at a pinch. So, what’s under your boot floor or hanging off the back door of your vehicle, and what are its pros and cons?
A full-sized spare is the same as the other four wheels on your car – same-sized wheel, same-sized tyre.
Aside from the need to ensure it’s kept inflated and in roadworthy condition, there are no conditions for its use. Once you’ve changed onto it you can drive normally and for as long as you need to. All you need to do is make sure you get the flat tyre fixed so you’re not caught out the next time you puncture. Simple.
Skinnier than a full-sizer, these allow car makers to make better use of the available space – often (but not always) to the benefit of boot capacity – while shaving a few kilos and saving some dollars as well.
There are shortcomings, however, when it comes to actually using them. Your car won’t steer, brake or grip as well as it would on four same-sized wheels, so they come with strict speed and distance limitations (typically 80km/h and a few hundred kilometres respectively, sometimes less for the latter).
If the car maker has taken advantage of a space-saver’s easier packaging, you might also find your punctured full-sized wheel just won’t fit in the space-saver’s hidey hole.
Sometimes packaging any kind of spare into a car just isn’t possible or it will have different-sized front and rear wheel/tyre combos, making any spare a 50/50 bet.
This is the answer to that conundrum and, in theory, it makes sense. Just hook up the 12V compressor/puncture-sealant combo to the punctured tyre, flick the switch to ‘on’ and watch the magic as the goo seals the puncture and the tyre inflates.
These sealants, however, are typically only able to seal very small holes – slash a sidewall and you’ll be waiting for a tow truck. They're generally intended just to get you to a tyre shop for a repair, so similar speed and distance limits to space-savers apply. The latex-based sealant also has an expiry date, meaning you’ll pay to replace it even if you don’t use it.
Another solution to the ‘no space for a spare tyre’ problem, run-flat tyres have an internal structure that allows them to be driven on while punctured. Aside from the packaging benefits of not needing to accommodate a spare or any kind of puncture-fixing apparatus, they are safer in a flat-tyre scenario because they don’t flatten entirely.
But it’s not all good news. Rather than just changing the tyre and driving on, you must drive straight to a tyre shop to get it repaired or replaced and you’ll have to adhere to strict speed/distance limits along the way. Run-flat tyres typically cost more than traditional ones, too, upping the replacement cost.