The Run-flat technology (tires with emergency running properties) is on the rise again. Although a few years ago the run-flats seemed to run out of steam, now the market share is significantly rising again. In an interview with Sales Manager at “Wheels” and Key Account Manager at “Delticom” Timo Eisen we talked about the pros and cons of run-flat tires, the price and safety of run-flat technology, what tire manufacturers offer for run-flat technology and what to look at when choosing run-flat tires.
TIRE.CA: Good day, Timo!
Timo Eisen: Hello, Tetiana!
TIRE.CA: Everyone knows that the tire plays a particularly important role in driving and safety. There are many new technologies that improve driving safety. One of these technologies is Run-flat or Run On Flat. What are run-flat tires and how does the principle "run flat" work?
Timo Eisen: Run-flat tires are still roadworthy even when the air pressure inside the tire falls, at least for a certain distance and at low speed. Due to the considerably reinforced side walls of the run-flat tires, they can carry the weight of the vehicle without air. The specially designed tire beads also prevent the tire from coming loose from the rim. The run-flat principle is therefore based on a self-supporting reinforced sidewall of the tire. This prevents pinching the tire side between the road and rim, as well as slipping of the tire in the rim well. In a nutshell, that's what a run-flat tire is and how it works.
TIRE.CA: It is a pretty interesting technology in my opinion. How can one recognize a run-flat tire?
Timo Eisen: Each tire has an appropriate marking on the sidewall indicating the size, manufacturer, model, DOT and other details of the tire. Run-flat tires have another special marking. However, this varies depending on the tire manufacturer. The label may be, for example, ROF, RFT, EMT, RCS, SSR, ZP for zero pressure, or DSST. Or simply "RUNFLAT." But there is always a special mark on the sidewall of the tire.
TIRE.CA: Thank you! And what about the trade? Do you have to look at the tire to see if it has the run-flat technology?
Timo Eisen: No, of course, if you are looking for such a tire, you have to check the tire sidewall to see if it is a run-flat tire. This then stand for these mentioned manufacturer identifications. These manufacturer's markings are included in our web shop, for example, if you are looking for a corresponding tire. That means, for example, you can filter for certain brands of tires with run-flat features and get there online exactly those shortcuts reproduced, which are then also found on the tire.
TIRE.CA: And what are the advantages and disadvantages of run-flat tires?
Timo Eisen: The biggest advantage is clearly the safety. Even with a sudden drop in pressure or with creeping pressure loss, it is safe to continue journey by car, as you can control the vehicle. A sudden pressure loss, the classic puncture, on the other hand is life-threatening and overwhelms many drivers, especially on the highway at high speeds. It is different with run-flat tires, because the onward journey is guaranteed with the usual tire damage. An otherwise require wheel change at life-threatening places, such as at the hard shoulder on the highway, on rural roads or in long tunnels, is then eliminated. Another major advantage is the comfort. In the event of damage, you do not have to do the wheel change yourself or by a breakdown service, but you are usually able to directly contact the dealer because of the large diversity of the run-flat tires. With use of run-flat tires, you don’t need to carry any spare wheels, which in turn increases the compartment volume by up to 80 liters. Another advantage is that the weight of spare wheel is eliminated and so energy and fuel are saved. But advantages come together with disadvantages. They can be seen in the price. Run-flat tires are more expensive than conventional tires. The weight of a run-flat tire is also slightly higher due to the design of its run-flat property. More weight always means energy expenditure, which entails a low additional consumption. At the current stage of development, however, this is largely at the level of conventional tires.
TIRE.CA: Great, thank you! One of the main advantages of run-flat tires is that you are still mobile in case of damage. How far and how fast can you drive with a damaged tire?
Timo Eisen: Range and speed are of course limited, because in case of damage, the tire is depressurized. The well-known manufacturers specify a speed of up to 80 km/h, as well as a range of about 80 km in the damaged state. However, higher speeds or longer ranges are not recommended. If a vehicle is equipped with run-flat tires in the factory, you will find the specific emergency distances and speeds in the vehicle manual.
TIRE.CA: Do the run-flat tires also have the so-called fuel-saving technology?
Timo Eisen: The run-flat tire naturally saves the weight of a spare tire, but it also requires a little more energy because the run-flat tire is heavier than conventional tires. I would say that is about to outweigh. A fuel-saving tire, namely a tire with low rolling resistance, is not automatically equivalent to a run-flat tire. However, fuel-saving technology and emergency running properties are not mutually exclusive.
TIRE.CA: Which brands offer run-flat technology?
Timo Eisen: There is now a wide mix of brands in different price segments. Some of these manufacturers include Bridgestone, Michelin, Continental, Goodyear, Dunlop, Pirelli, as well as Falcons, Nokian, Kumho, Hankook, Nexen, Yokohama and others. There are now many brands that are available in various sizes.
TIRE.CA: And does the price depend on the brand?
Timo Eisen: In terms of prices, it needs to be said that a run-flat tire is more expensive than a conventional tire due to its special design and technology. The gradations within the brands are in the usual brand structure to each other, so for example, a Michelin tires will be significantly more expensive than one from Hankook.
TIRE.CA: I understand that. And can the run-flat tires be mounted on all vehicles?
Timo Eisen: The use of run-flat tires is always recommended for vehicles that are factory-equipped with such tires. In these vehicles, forces acting on the suspension are taken into account by the stiffer tire sidewalls. In addition, the vehicle needs a tire pressure monitor to be equipped with run-flat tires. It is very important that the driver notices when the tire loses pressure. Therefore, the tire pressure control is mandatory. Run-flats are thus generally recommended on vehicles that have such equipment since production at factory or to vehicles which can be additionally equipped.
TIRE.CA: Can run-flat tires actually be driven on a "normal" rim?
Timo Eisen: Yes, that is possible. But there is a risk that the run-flat tire will jump off the rim when there is pressure loss. This can happen in an extreme situation, for example in a sharp corner or during an evasive manoeuvre when the tire is empty. Here the advantage lies of so-called Extended Hump rims. These are rims that have the technical name EH2 or EH2 +. Due to the special shape of these rims more stability and safety for the tire is given and the risk that the run-flat tire can jump off from the rim is eliminated. This is not a requirement though. You do not necessarily need a corresponding run-flat rim with run-flat tires and consequently you do not necessarily have to use run-flat tires for the run-flat rim. It may be mixed there.
TIRE.CA: BMW plays the pioneering role in run-flat tires and equips several models with this technology as standard. Are run flat tires mandatory for any BMW models?
Timo Eisen: Although BMW is considered a very early pioneer of this technology, the use of this tire system is not mandatory. It should be noted, however, that these vehicles usually have no breakdown set or spare wheel on board. So, if a vehicle is designed by the manufacturer to use run-flat tires and you swap these run-flats for conventional tires, then you have to know that the mobility in case of damage depending on the vehicle may no longer exist. Even if you later equip the vehicle with a different breakdown set, you have to remember to procure these on-board resources and to deal with whether enough secure storage space is available for them.
TIRE.CA: Good, thank you. I would like to ask a bit more about the tire assembly. Where can the run-flat tires be mounted and can you do it yourself?
Timo Eisen: Run-flat tires should always be mounted by a qualified dealer. There are so-called WDK (The Trade Association of the German Rubber Industry) certified dealers. Such a certificate documents is a quality standard regarding the training of fitters and assembly machines. The customer who is interested in tires can quickly and easily select a specialized dealer from his area from more than 10,000 assembly companies, for example www.tire.ca . Self-assembly is generally not recommended because the tires require special assembly and can be easily damaged, which significantly increases the risk of accidents.
TIRE.CA: And what should be considered when changing run-flat tires? You said that qualified dealers are important?
Timo Eisen: The handling of run-flat tires should always be trained and then the assembly is neither complicated nor expensive. However, an unspecialized person with inappropriate equipment can apply so-called bead injuries to the tire, which can then become critical as soon as the tire becomes hot or is heavily stressed. Run-flat tires belong in the hands of specialist dealers.
TIRE.CA: Well understood. Many Thanks. Could you maybe tell me if a burst run-flat tire can be patched?
Timo Eisen: That's a very interesting question. The patching of run-flat tires is not recommended or even rejected by the manufacturers. That is, a tire that has a puncture wound, a damage or something else is not repaired but replaced. This is due to the design and the special sidewall of the tire; the consequential damage of a flat ride does not necessarily look.
TIRE.CA: And what about run-flat and TPMS?
Timo Eisen: TPMS stands for tire pressure monitoring system. A run-flat tire does not necessarily show the pressure loss compared to a conventional tire. A run-flat tire with pressure loss feels when driving, e.g. in city traffic, quite "normal". This is dangerous, because then you are already in case of damage and cannot follow the limitations of the tire manufacturer in terms of speed and residual mileage of the tire. That is why it is important that vehicles with run-flat tires have an appropriate tire pressure monitoring system. For vehicles that are designed for run-flats at the factory, these tire pressure monitoring systems are always on board.
TIRE.CA: Good. That would be all. Many thanks for your help.