The battle to cut CO2 by car manufacturers has encompassed many aspects of car design and development.
Apart from the more obvious tweaks that make engines and gearboxes operate more efficiently, some changes have also focused on aerodynamics, wheel design and tyres.
Weight saving has also made an important contribution, from the materials used to fitting a puncture repair kit instead of a spare wheel.
But according to the RAC’s latest vehicle fault analysis data, puncture repair kits are no substitute for a spare tyre and contributed to more than 4,000 days of downtime for fleet vehicles in 2009.
The total figure – 4,111 days – represented more than a quarter of the near 15,000 days lost to vehicle downtime last year through breakdowns, of which about 30% were due to avoidable faults.
The RAC claims it would be less costly for businesses to choose cars with spare wheels fitted or to select them as a dealer-fit accessory.
“Spare wheels began disappearing in the mid-nineties with LPG vehicles which used the spare wheel well for the tank,” said Steve Whitmarsh, senior partnership manager, RAC Fleet and Commercial Services.
“When the Government linked CO2 emissions to VED and BIK tax the need to save weight brought a renewed focus on removing spare wheels and the trend for not including a spare tyre continued.”
He adds that manufacturers now frequently remove the spare wheel to reduce CO2 emissions by saving weight and to save money on the cost of the spare wheel itself.
Whitmarsh says the problem of increased downtime has escalated as a result, as carrying a spare wheel would have resulted in a relatively short delay compared with using a puncture repair kit.
And he believes using the kits themselves presents difficulties for many drivers who don’t know how to operate the devices.
“Advice and training on how to use repair kits and space-savers would be invaluable to fleets to ensure greater up-time for their vehicles,” said Whitmarsh.
“However, it is also a question as to whether spare tyre replacement devices are fit for purpose for fleets, and there may be duty of care implications for fleet managers to consider.”
Puncture repair kits usually comprise an air compressor that plugs into a car’s 12-volt power socket and a container of liquid gum, or an aerosol containing foam. Whichever type is used, the repair is only temporary and the tyre must be replaced as soon as possible, forcing up costs.
But if the damage is in the tyre sidewall, or if it’s a major blowout with shredding, the repair kit will be useless.
Whitmarsh says: “Saving on the transaction price of buying the vehicle can be nullified by having no spare.
“Once a can of foam has been used on a puncture, the tyre has to be replaced – it cannot be re-used.
A new tyre could be £200, whereas a puncture repair is often free at many tyre-fitting centres.”
Repair kits also extend downtime caused by a puncture by up to half a day.
Run-flat tyres are a safer alternative allowing a vehicle to be driven some distance before replacing the tyre – useful if the puncture happens several miles away from a fast-fit outlet or dealer.
“One premium brand manufacturer sensibly began fitting run-flat tyres instead of providing a spare wheel,” Whitmarsh says.
“This is the only suitable compromise for not including a spare wheel as it will keep you moving until a repair can be made.
"Anyone who has changed a spare wheel on the hard shoulder will know just how valuable run-flat tyres are.”
But run-flats can also increase costs as they are more expensive to replace than standard tyres after a serious puncture or when they wear out.
Whitmarsh says fleets should now call time on the practice of repair kits and spend money on an aftermarket spare wheel, that would have no implication on a vehicle’s CO2 emissions recorded on the V5 document.
“Repair kits are absolutely no substitute for a spare wheel or even a space saver,” he said.
“Fleets should consider specifying a spare wheel as a dealer-fit accessory. The costs of doing so will be offset by reduced downtime and tyre replacement costs.”