History of Run Flat at BMW?
The first vehicle to have Run Flat tyres fitted in the BMW Group was the Z8 and MINI with great success, then Z4 E85/86, 5 Series E60, 6 Series E63/64, 1 Series E87/81/82/88, 3 Series E90/91/92/93, X5 E70 and X6 E71.
What BMW vehicles do not have Run Flat tyres yet?
Currently the following vehicles do not have Run Flat yet: X3, 7 Series and M products.
Why has BMW developed this system?
Every driver’s nightmare: a tyre suddenly blows at high speed on the motorway, the car slews and can be brought under control only with difficulty. A hair raising situation even for experienced drivers or in bumper to bumper traffic on a secondary road where there is hardly enough room to safely leave your car without risk, BMW have found a solution in a set of safety tyres including a Tyre Pressure Monitor (TPM) system. Run Flat tyres therefore provide vital safety benefits.
What is the availability of Run Flat tyres?
BMW SA has a network of dealers across the country that not only will be able to supply you with the required tyres, but are also able to fit them to the required quality standards. Most tyres suppliers also supply Run Flat tyres. A further extension of our support for this technology is through BMW-On-Call.
How far can one travel with a punctured Run Flat tyre?
The flexible rubber springs in the side walls of the tyres ensure the tyre largely retains its lateral support even in the event of sudden, total pressure loss and remains operable within certain limits (150 km partly laden at max. 80 km/h, 50 km fully laden and 250 km in a vehicle that is not heavily loaded). In the case of typical punctures with very slow pressure loss, the vehicle can still be driven for approx. 500 to 2000 km at max. 80 km/h as from the TPM warning.
Can I replace a Run Flat tyre with a standard tyre?
Technically Yes, BMW however does not recommend this (with the exception of an emergency situation where a Run Flat tyre is not available. In this case the tyre must be replaced with a Run Flat tyre at the earliest opportunity). The reason for this is that no spare wheel will be fitted to vehicles with Run Flat, therefore there is the risk of a situation of getting a puncture and having no spare wheel and no run flat tyre to drive on. Note: 5 Series (E60) 530i, 530d, 545i and 550i are the only models to have Run Flat technology and an emergency spare wheel.
What is the price of Run Flat tyres compared to normal tyres?
The Run Flat tyre is approximately 15% to 35% higher than a normal tyre. (Two reasons for this. Firstly, it is a more expensive technology. A plasma screen costs a little more than a normal TV, doesn’t it? Secondly, as more and more manufacturers join the Run Flat parade, the tyre manufacturers will produce and sell higher volumes at a lower cost.)
Will I get the same mileage out of the Run Flat as I do with a normal tyre?
How do you identify a Run Flat tyre?
There is an RSC identifying mark on the outer side wall of the tyre. (Most tyres are marked RSC, but some tyres are also marked as RFT or, RunOnFlat.)
What does RSC stand for and how does it work?
(R-un flat S-ystem C-omponent). Indicating that these tyres are merely one component in a more comprehensive safety system.
How do I initialize the system?
Regardless of whether your car is equipped with TPM or the Tyre Pressure Control (TPC) system, reinitialisation must take place every time the tyre pressure is adjusted or when wheels/tyres are changed in order to record the current pressure required. This calibrating process must be performed when the tyres are cold, to prevent the values from being falsified by higher temperatures. Initialization starts when the Tyre Pressure Monitor/Control button is pressed until the indicator lamp in the instrument cluster lights up yellow. After a brief driving time, from a speed of 15 km/h, the system learns the new reference values and the yellow indicator lamp goes out. The indicator lamp lights up red if a pressure loss is identified by the system. The driver is alerted to a system failure by the indicator lamp in the instrument cluster lighting up yellow. (This is the method for some of the older BMWs. In the newer models such as the 1, 3, 5, X5 and X6 it is done either through the iDrive if equipped, or through the On-Board computer.)
Do other manufacturers use Run Flats?
Recently, Audi and Mercedes have also begun to recognise the advantages of Run Flat tyres. Mercedes now offers them as an optional extra for every new model. Audi is about to follow BMW’s lead and will introduce run flat tyres as standard for its vehicles in the near future This will inevitably lead to these tyres becoming even more readily available from tyre retailers.
Is it true that Run Flat tyres are subject to more wear than conventional tyres?
No. If both tyres are subject to the same stresses, they will both experience equal wear. Vehicle durability tests performed on identical test tracks have confirmed this time and time again during the design and development process, using different BMW Group vehicles. However, Run Flat tyres respond a little more sensitively to changes in tyre pressure – to develop correct user behaviour, it is necessary to understand the function of the Run Flat indicator or TPM (Tyre Pressure Monitor). This does not replace regular pressure checks. In addition, the new models are consistently more powerful than the old ones. While this enables more dynamic driving, it also exposes the tyres to increased stresses and thus may reduce their service life a little.
Is it true that the ride comfort achieved with Run Flat tyres is inferior to that of conventional tyres?
The ongoing design optimisation of Run Flat tyres and the adjustment of chassis and suspension systems have eliminated the initial drawbacks of Run Flat technology in terms of ride comfort. The new BMW Group vehicles have exactly the desired balance between handling ability and ride comfort.
Why do Run Flat tyres have flattened shoulders?
For optimum handling, high-performance (HP) tyres have a smaller tread depth in the shoulder area than in the wider longitudinal grooves that contain the wear indicators. So what looks like wear on the outside shoulder of the tyre is in fact not tread wear at all.
At the end of the day, a spare wheel gives you an added feeling of safety – doesn’t it?
The spare wheel has not been dropped – it has been replaced with a better and safer solution. With Run Flat technology, what you effectively have is four spare wheels. The emergency capabilities of Run Flat tyres listed in the user manual and in advertisements all relate to completely deflated tyres (0 bar): in this condition, which in practice is very rarely encountered, Run Flat tyres are designed to still last a considerable distance. Driving carefully (max. 80 km/h), with four persons on board, this distance averages around 150 km, or 50 km with maximum axle load or 250 km with a light load. This “Run Flat distance” represents the built-in reserve of the Run Flat tyre.
Can I use conventional tyres on a BMW that was designed to have Run Flat tyres?
For all new vehicles which have been specifically designed with the Run Flat technology in mind, as well as all future vehicles of this type, conventional tyres can theoretically be used, but their use would not make sense. The engineering parameters and specifications of Run Flat tyres and conventional tyres are quite different, due to their different design concept; providing equally optimised conditions for both types of tyres would require a different vehicle and suspension design.
What is the difference between the Run Flat TPM (Tyre Pressure Monitor) and TPC (Tyre Pressure Control)?
The Run Flat indicator indicates tyre failures, while TPC checks the tyre pressure. TPC monitors tyre pressure on an ongoing basis, based on direct measurements. The Run Flat indicator does not measure tyre pressure directly; it detects differences in the wheels’ rotational speed and thus can only indicate major pressure changes in one tyre compared to the others. This is sufficient to effectively address the most frequent causes of pressure loss encountered in driving, and the resulting tyre failures. The most common situation is a drop in pressure in one tyre. And the Run Flat indicator is enough to indicate to the driver that one of the Run Flat tyres is losing pressure.
How should I deal with complaints about “abnormal tyre wear”?
When customers complain of “abnormal wear” and it is suspected that this may be due to a lack of pressure maintenance (manual pressure checks), the control units for the Run Flat indicator and TPC should be checked for the mileage count when the most recent initialisation took place. Based on this mileage count, it is usually possible to guess when the most recent initialisation and pressure check were performed. If this was a long time ago, then it may be assumed that tyre pressure was not checked and maintained on a regular basis.
Should front and rear wheels be swapped on a regular basis?
Swapping tyres from front to back is not recommended for BMW vehicles, since it would impair dynamic performance. Tyres used for longer periods on cambered rear wheels are particularly likely to cause an unpleasant ride when mounted on the front wheels. In addition, such an instruction would run counter to the trend for longer and longer customer service intervals.
Is it possible to repair a damaged Run Flat tyre?
BMW does not recommend tyre repairs. Tyres are a major safety component and should never be used in a “weakened” condition. This is particularly important for high-performance tyres, be they of conventional or Run Flat design. Note that we are not saying that you “cannot” but rather that we don’t “recommend”. Even if you refer back to a BMW owner’s manual from 1982 (long before Run Flat) you will find that “BMW do not recommend the repairing of tyres”. The procedure for repairing a Run Flat tyre is however the same as that for repairing conventional tyres, i.e. any standard puncture (in the tread area) can be repaired by an authorised specialist vulcaniser. The vulcaniser together with the customer however assumes responsibility for the work carried out. BMW cannot assume product liability for repaired tyres. This would have been the case with a conventional tyre as well. BMW however recommends that a tyre should only be repaired in an emergency, subject to the above. The repaired tyre should then be replaced at the earliest opportunity. A Run Flat tyre may also not be repaired if the vehicle has been driven in “Run Flat mode” (in other words, with 0 tyre pressure). Note that this is again exactly the same as what would have been the case with conventional tyres.
We hope that this clears it all up for you. It should also be mentioned at this point that if at anytime you have a question about Run Flat tyres, or you experience any problems, BMW On Call are there to help and are fully equipped to do so. Just in case you don’t have it, their number is 0800 600 777, and the BMW Customer Service number is 0370 5050 160
. If you are still in doubt, speak to the Aftersales department of your local dealer.
Further reading – RFT: Tramlining