As with any pursuit meant to enhance a single quality or area of performance, the drive toward greater fuel economy sometimes requires compromises in other areas.

There's often give and take when it comes to increasing efficiency, whether it entails downsized engines, more complex electrified powertrains, or higher sticker prices.

But fuel economy may slowly be leading to the disappearance of a common piece of equipment: the spare tire.

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Automakers have eliminated spare tires in 29 million vehicles over the last 10 model years, according to AAA.

Run-flat tires and tire-inflator kits have led some carmakers to get rid of spare tires in new models, but AAA thinks spares are the only adequate solution to a flat tire.

Because of their "limited functionality," the alternatives "cannot provide even a temporary fix for many common tire-related problems," the group said in a statement.

Leaf Tires

Leaf Tires

It claims 36 percent of 2015-model-year vehicles were sold without spare tires, compared to five percent of 2006-model-year vehicles.

At an average four pounds, a tire-inflator kit saves about 30 pounds of weight, AAA notes.

But it claims they are not as effective in getting cars back on the road after a puncture as a spare tire.

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Inflator kits--which generally include a sealant and a compressor to re-inflate the tire--only work when the tire is punctured on the tread and when the object that caused the puncture is still lodged in the tire, AAA claims.

It says in-house testing has shown that tire-inflator kits don't work when the puncture occurs in the tire sidewall, or when the object that caused the puncture is no longer in the tire.

Some kits also cost up to $300 per use, making roadside repairs significantly costlier to drivers, AAA claims.

2016 Toyota Prius - first drive, Laguna Niguel, CA, Nov 2015

2016 Toyota Prius - first drive, Laguna Niguel, CA, Nov 2015

It also notes that these kits generally have a limited shelf life--averaging four to eight years.

Yet if spare tires are in shorter supply, so are the skills needed to make use of them.

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More than one in five Millennial drivers (age 18-34) do not know how to change a tire, whereas nearly 90 percent of drivers aged 35 to 54 do, according to AAA.

So it's possible that in the future, many drivers won't bother trying to change their own flats at all.

They may just call roadside-assistance services like ... well, AAA.


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