Automakers are losing weight by shedding that spare tire.
More passenger cars are rolling off assembly lines with no jack, wrench or fifth wheel in the trunk as the U.S. government seeks more aggressive fuel economy targets and consumers demand savings at the pump.
"There are increasing pressures to find alternatives," said Dave Cowger, group manager of tire engineering at General Motors.
The spareless effort, for now, is playing out predominantly at GM where most of its nearly two dozen car and crossover models in the United States do not offer spare tires as standard equipment.
But the trend can also be spotted industrywide, mainly on overseas models and frequently on cars designed for increased efficiency.
"For customers who want an extra wheel, they can get a compact spare as an option. That's the way we try to package it," Cowger said.
Virtually all cars had spares just a few years ago.
That has changed as 20 percent of the 1.2 million sedans, compacts and other passenger cars sold in the United States this year through October came without spares as standard equipment, according to data from online buyer research group Edmunds.com.
Full-size spares remain standard in big-selling large pickups and SUVs that make up more than half of industry sales because they are commonly used as work trucks on unfriendly road surfaces or for towing.
These include Ford F-Series pickup, the best-selling vehicle in America, and the Dodge Ram pickup.
"We'll still offer one as long as the customer expects it," said Vince Muniga, a spokesman for truck-heavy Chrysler.
The top-selling passenger car in the United States, the Toyota Camry, also comes with a spare, as do popular Ford compacts and sedans.
GM and other automakers, however, are producing spare-free vehicles, part of a strategy to answer an Obama administration plan to double average fuel efficiency requirements to 54.5 miles per gallon by 2025.
Losing the "donut" wheel, the compact spare offered in many cars for decades, and its related equipment, can save more than 25 pounds (11 kilograms), industry experts said.
That yields an average savings of less than 1 mpg, but it is part of an efficiency strategy that capitalizes on incremental gains. For instance, a spareless trunk was one of 42 changes made by GM on manual Chevy Cruze Eco models to reach an estimated 42 miles per gallon on the highway.
AAA data shows that tire problems steadily represented about 12 percent of more than 3.5 million calls annually to the motorist group for roadside assistance from 2000-2010. Despite the figure, automakers believe safety advancements have made the spare tire less crucial.
They point to tire pressure monitoring systems and roadside assistance programs, like GM's OnStar offering, that make it less likely motorists will get flats or be stranded by them.
Vehicles without a spare usually feature a trunk-mounted inflator kit that includes a mini compressor and a sealant to close small holes and reinflate damaged tires. Automakers and consumer groups stress inflators are designed to seal minor punctures, not repair a large cut or a damaged sidewall.
Toyota's Prius hybrid has a spare but the plug-in version carries an inflator, standard, as does the all-electric Nissan Leaf. The Fiat 500, a subcompact that Chrysler is hoping will revive its U.S. car lineup and boost fleet fuel efficiency, also features an inflator.
Hyundai, BMW, and Mercedes also offer inflators in certain vehicles.
John Nielsen, director of auto repair and buying services for AAA, cited anecdotal evidence of drivers who were surprised by the lack of a spare tire.
"The feedback we've received has centered on not having a spare and not knowing about the inflator kit," Nielsen said.
"The number of examples are small and would seem statistically insignificant, but the motorists that find out they don't have a spare in a moment of need consider the issue quite significant."
GM is showing some flexibility on the issue. Responding to demand last year from customers who wanted a spare, GM added them standard to those 2012 Cruze models that realize extra gas mileage from a more efficient transmission.
Houston-area Chevy dealer Carroll Smith said a typical consumer response is that it is smarter to have a spare and his showrooms will order one ahead of time, if it is available.
(Reporting by John Crawley; Editing by Tim Dobbyn)