Run-flat technology maximizes safety


Very low lateral expansion and its high volume compressibility make it possible for Cellasto® to be used for shock absorption and damping where the surrounding construction space is limited.


Even in a capsulated environment Cellasto can be compressed to more than 60% of its thickness without any lateral expansion. As a result of its special combination of properties, such as excellent damping, high resistance and excellent static and dynamic long-term behavior, Cellasto can withstand the highest strains permanently.


The new safety limousine from BMW also fulfills the highest requirements in terms of safety: the BMW 540i protection protects the passengers even against being fired at with a 44 magnum.


Among other things, the run-flat-tire developed especially for BMW by BASF Polyurethanes ensures driving safety. This ‘wheel-in-a-wheel’ ensures a safe continuation of the journey, even in cases of destroyed and pressure-less tires. The driver does not have to compromise on the handling of the vehicle, even at speeds of up to 80 km/h. The Cellasto wheel assumes the supporting function of the tires. Even driving over the edge of the curb is possible without any damage to the system.


Cellasto marked the beginning of a new era in the manufacture of emergency wheels. Cellasto's volume compressibility makes for a completely new type of assembly. For the first time, an emergency running element consisting of just one part can be mounted on a one-piece standard rim. For this, the Cellasto ring is buckled to such an extent that it can be moved over the rim horn, so assembly can be carried out on conventional lines.


In the manufacture of the Cellasto ring, polyester webbing is placed in the mold at the start. Later, in use at high speeds, this takes on the role of positioning the emergency wheel which is radially pre-stressed on the rim, preventing the divergence of the ring as a result of centrifugal force.


In the event of running on a flat, the steel breaker tire overtakes the emergency wheel with a defined relative speed as a result of the difference in diameter. Friction energy is generated, which is converted into heat. The outermost webbing protects the Cellasto tire against premature thermal destruction, increasing its running performance in an emergency.


In the following production step Cellasto is foamed into the mold by means of a casting technique developed by BASF Elastogran. In the casting process, the A components of the material (made up of a polyester diol and naphtyl diisocyanate) are mixed with the B components (made up of cross-linking agents, stabilizers and catalytic converters). The skill here lies in mixing two different viscosities and mixing ratios homogeneously within as short a time as possible.


After releasing the emergency wheel from the mold, the material is tempered at 230°F (110°C) over a period of 16 hours. Then the ring is counterbalanced by means of pins made of thermoplastic polyurethane. Now the emergency wheel can be assembled. Within the framework of a cooperation arrangement, BASF Polyurethanes is currently working on the development of an emergency wheel with a hard external shell. These elements could also be assembled with conventional lines on standard rims.