Run-flats still function for optimum safety

“The benefits of this tyre technology have proved themselves time and again with owners who have been unfortunate enough to get a puncture”

Tyre manufacturers estimate that by 2008 one in four new cars sold will not be equipped with a spare wheel in the boot. The age-old practice of changing a punctured or damaged tyre on the roadside will increasingly be confined to the history books as vehicle manufacturers turn to fitting run-flat tyres to models. From a safety perspective, not only do run-flats mean the end of the dangerous practice of jacking up a car on the roadside to change wheels, but also the new technology means that a motorist can continue driving for up to 150 miles at 50mph with a puncture depending, on model and tyre make.

Run-flat tyre supporters also point to their weight-saving advantages – no spare wheel in the boot reduces weight and therefore improves fuel economy – and the elimination of the “fifth wheel” means additional boot space for load-lugging. It is those advantages that have led BMW to increasingly fit run-flat tyres on the majority of its models. Without doubt, the German marque is comfortably in pole position in the fitting of run-flats to production models with the 1-Series, 3-Series, 5-Series, 6-Series and Z4 all having the tyres as standard fit, with only a handful of discrepancies across the ranges. Continuing run-flat technology developments will result in BMW being able to fit the tyres to the rest of its models, including the range-topping 7-Series and X3 and X5 off-roaders.

Meanwhile, opponents of run-flat tyre technology point to their additional cost – unlike traditional tyres, in the event of a puncture they cannot be repaired, but must be replaced – and claim a harsher ride and increased road noise due to the stiffer sidewalls of run-flats. BMW, which fits run-flat tyres from a number of manufacturers to its models, counters such claims by saying that the suspension on its cars – the first model to feature run-flat tyres was the latest generation 5-Series in 2001 – has been designed to suit the firm sidewalls of run-flat tyres. A company spokesman says: “The benefits of this tyre technology have proved themselves time and again with owners who have been unfortunate enough to get a puncture. Unlike cars with conventional tyres that experience a slow puncture or even a blow-out situation, the run-flats still function for optimum safety.”

He adds: “Conservative advice also says a driver can continue for 150 miles at 50mph with a punctured run-flat tyre. However, during testing expert drivers continued driving on a deflated run-flat tyre for more than 600 miles before the tyre eventually failed.” In addition to motorists changing damaged tyres at the roadside, more than one million tyre incidents are covered by the major breakdown services every year and more than 4.8 million punctures were suffered by UK motorists in 2004. Despite run-flat technology also eliminating the nuisance and dangerous activity of wheel changes on a main road or motorway hard shoulder, few manufacturers have followed BMW’s lead.

“The only standard on which the tyre industry appears to agree on is that cars fitted with run-flats can be driven at speeds of up to 50mph in run-flat mode”

Audi, for example, offers run-flat tyres as an option on a number of models, including the new A4, which went on sale earlier this year. Asked why run-flats were not fitted as standard on some models when the rival German prestige marque had already adopted the technology, a spokesman says: “The decision to offer run-flat technology as an option has been taken based on Audi customer feedback, which indicates that UK Audi drivers generally prefer conventional wheels and tyres with a full-size spare wheel. We therefore take this route wherever possible in the Audi range, except in cases where space may be compromised.” While Audi says it will continue to monitor market trends it has no plans in the “foreseeable future” to fit run-flats as standard.

Meanwhile, Citroën, which for 40 years until the mid-1970s was owned by leading tyre manufacturer Michelin and continues to exclusively fit the brand’s tyres across its model line-up, does not promote run-flats. Indeed, even when so-called spacesaver tyres were promoted a few years ago the French marque steered clear of the technology. For all vehicle manufacturers, but particularly volume manufacturers, keeping list prices to a minimum is a major issue and the standard fitting of run-flats would add cost both up-front and in terms of replacement in the event of tyre damage. That is believed to be one of the factors in Citroën not embracing run-flat technology. A spokesman says: “We are known for our value for money. We have looked at run-flat tyres, but have no plans to fit them to our models in the near future.”

A weighty issue

All major tyre manufacturers are promoting run-flats and they have been introduced in response to vehicle producers looking to eliminate the “dead weight” of the spare wheel, according to tyre makers in order to reduce the weight of the vehicle and therefore improve fuel consumption, gain space in the boot and allow innovation in car design. Some tyre manufacturers offer two types of run-flat tyres – wheels fitted with an inner support ring on which the tyre rests at zero inflation and so-called self-supporting tyres, which is effectively a standard tyre with sidewalls reinforced by special rubber compounds.

However, the different inner support ring technologies used to fit the tyre to the wheel by tyre manufacturers means that no universal standard has been agreed upon, so moving from one tyre make to another is impossible. Indeed, it is not recommended to switch between self-supporting tyre manufacturers. In addition, the range of run-flat tyres in run-flat conditions is also hugely variable, with figures ranging from 50 miles to 150 miles possible depending on tyre make and car model. Indeed, the only standard on which the tyre industry appears to agree on is that cars fitted with run-flats can be driven at speeds of up to 50mph in run-flat mode. To draw the driver’s attention to an imminent puncture or a gradual loss of air in the tyre, all vehicles fitted with run-flat tyres are equipped with an automatic tyre pressure monitoring gauge. In the event of a loss of pressure, it informs the driver – usually optically and acoustically – via the dashboard display. This then allows the driver to adjust their speed and make plans to top up with air at the next available opportunity or divert to a tyre centre.

The Tyre Industry Council and British Rubber Manufacturers’ Association says it is vital that drivers check both the quoted distance and speed permitted in deflated conditions as they can vary according to the tyre and vehicle manufacturer concerned. The organisations add: “In the course of running in a totally deflated or significantly under-inflated condition the tyre structure is subjected to high stresses and hence may become weakened and permanently damaged, rendering the tyre both unsuitable and unsafe to repair. When a standard tyre is run deflated (or significantly under-inflated) there are visible symptoms, which indicate that damage to the tyre’s structure has occurred. “However, because of the reinforced sidewall structure of a run-flat tyre, these symptoms associated with use in a deflated or partially inflated condition are likely to be masked and be invisible even if they are present. Even a fully-qualified tyre repairer may not be able to detect run-flat damage. For these reasons, and in the interests of safety, we do not recommend the repairing of run-flat tyres.”

The organisations also say:

• Run-flat tyres should not be intermixed on a vehicle with conventional tyres or retro-fitted
• It is advisable that the same make and type of run-flat tyre is fitted
• The tread rubber compound used in run-flat tyres is generally the same or very similar to that used in conventional tyres so tyre wear rates between the two types should be similar
• Run-flat tyres should not be fitted to a vehicle that is not equipped with a tyre pressure monitoring system

The fleet options

Fleets must face up to a trade-off between safety and cost in the decision over whether or not to embrace run-flat technology.

In addition, run-flat tyre replacement is restricted to the original manufacturer, mobile tyre fitting is not an option on run-flats that come with an inner support ring and run-flat tyre supply at some fast-fit outlets is limited. ALD Automotive calculates that BMW’s decision to fit run-flats as standard adds, for example, £2.50 a month to the three-year/60,000 miles contract hire rate on a 3-Series and £4 on 5-Series model. In addition, the company points out, the cost of a new run-flat is typically 25-30% higher than a traditional tyre. However, as demand increases the price will, undoubtedly, reduce.

“The choice for fleet operators is based on balancing safety features and in-journey driver convenience with the increased cost and potential tyre replacement delay”

The company’s fleet services manager Csaba Ujvari says: “There is a cost difference at the moment between traditional tyres and run-flat tyres. But as more vehicle manufacturers embrace run-flat technology the price premium will reduce. “From a safety perspective, it makes absolute sense to fit run-flat tyres; the advantages are there for all to see and I am personally glad that BMW is taking the lead that it has. What price safety?” Rival contract hire company Masterlease says there are currently too few vehicles on its fleet of more than 100,000 company cars to accurately appraise some of the issues.

David Parkes, services support specialist at Masterlease, says: “There have been isolated instances where run-flats have created issues for individual customers and the use of run-flats presents the fleet industry with budgetary and service delivery issues as well as potential opportunities in road safety and vehicle operational areas. “We fully support innovation, improved safety standards and the increased convenience to customers and we will discuss all of the issues with our clients and will continue to investigate and appraise the products offered. “The choice for fleet operators is based on balancing the safety features and in-journey driver convenience with the increased cost and potential tyre replacement delay over the conventional tyre.

“In terms of benefit-in-kind taxation, run-flats possibly present a fuel economy issue in normal running, although verifiable evidence of this is hard to find. Time will tell if this should be a consideration.” Jamie Wiseman, maintenance manager at Lex Vehicle Leasing, says: “Run-flat tyres are fitted as standard to only a few models, such as the new BMW 3-Series. Run-flat tyres are currently about 20% more expensive than an equivalent standard tyre. As for wear rate, it is too early to judge from our fleet experience. We are currently running at 0.19% fitment on the fleet, which is obviously very low, but we see this growing as the likes of the 3-Series grows its penetration of the Lex fleet.

“Availability is currently low as there is not a great demand. However, usage is constantly monitored and stocks are being held at certain centres and their distribution hubs, so we shouldn’t see any problems in getting our cars’ tyres fitted with run-flats.” Kwik-Fit says due to limited demand it stocks replacement run-flat tyres at selected fleet centres. However, its regional “hub and spoke” depots stock a wide range of run-flats that can be delivered to centres within two hours.

Call for driver education

Risk management experts say run-flat tyres are a major safety feature and should be a consideration for motorists in choosing their new company car – although they all stress that driver education is vital. Duncan Vernon, road safety project officer, RoSPA, says: “Run-flat tyres can be a very useful safety aid so long as drivers know the limitations of the technology. For example, run-flats are only designed to be driven on for a short distance and at a relatively low speed. “The fact that their fitment to a vehicle removes the need for the driver to stop at the roadside in the event of a puncture is good because a potential hazard is removed.

“Drivers also need to understand that run-flats cannot be retro-fitted to vehicles that are not fitted with a tyre pressure monitoring system – the two technologies go hand-in-hand. Motorists also need to continue to regularly check tyre pressure and tyre condition – such checks cannot be ignored even if run-flats are fitted. “Run-flat tyres cannot be repaired and if punctured or damaged the whole tyre must be replaced, which can be expensive. However, there are safety benefits and undoubtedly as more vehicles are fitted with run-flats the cost will reduce.” Mark Edwards, head of training, IAM Fleet, says: “The arrival of run-flat tyre technology should be welcomed, as punctures and blowouts pose a bigger threat than they did in the past due to the greater volume and density of traffic on the roads. This in turn makes drivers more vulnerable, both in terms of the possible affects on vehicle stability due to a puncture and whilst attempting to carry out a wheel change. While recognising that cars fitted with run-flat tyres are only able to use a specific type of tyre to match their wheel rims, it is also important to remember that the technology is still relatively new and that this issue can and should be resolved.

Run-flats present pros and cons to drivers

“Run-flats bring a number of benefits, including that of preventing the driver from trying to change wheels at the roadside”

“The requirement for run-flat tyre vehicles to be fitted with a tyre pressure monitoring system is also a positive step from the risk management perspective, as it raises the driver’s awareness of what are ultimately the only physical points of contact between the vehicle and the road.” Agreement came from Les Hammond, director of risk management at Chesterfield-based Peak Performance, who says: “Run-flats bring a number of benefits, including that of preventing the driver from trying to change wheels at the roadside therefore decreasing the risk normally associated with this activity, but drivers must be fully conversant with the changes that run-flats can bring. “Speed, cornering, braking, accelerating, road holding in poor weather – all may be affected by operating on run-flats, and drivers must be made fully aware of any such performance changes and the appropriate modifications to driving style that may be required.

“It would be beneficial if the manufacturer allowed a prospective owner or buyer to see and feel such a system as part of the purchase. As was the case with ABS, many drivers did not understand the technology and were misinformed of the actual abilities of the ABS system, and we may see the same thing with run-flats if sufficient information and training is not provided.” He added: “The fitment of run-flat tyres is likely to mean that the emergency breakdown services will have to change their call-out procedures to include the question ‘do you have a spare wheel’ as the run-flat cannot be repaired or utilised.” Steve Johnson, of Drive & Survive, says: “It is quite difficult for an inexperienced or low mileage driver, particularly if in an unfamiliar car, to even detect that tyre deflation is in progress.

”The result is that vehicles tend to be driven for longer before the driver realises the problem and the tyre degrades to a dangerous state before the vehicle is brought to a halt. Experienced drivers tend to bring a vehicle with a deflated tyre to a halt smoothly and gently, whereas the less experienced, who have almost certainly never had to deal with this situation before, can panic and take drastic action. Stamp hard on the brakes with a deflated, or worse still destroyed tyre, and it will almost certainly lead to loss of control, ABS or not. ”Drivers just do not get the chance to practice dealing with a puncture whilst on the move, so anything that enables them to bring the vehicle to a halt safely must be an advantage, irrespective of cost.”