If you watch old movies, have a look at the cars of those times, you will certainly have noticed that they all have one, or maybe even two spare wheels. The plight of those early years becomes even clearer when you see the old racing cars in action, with a mechanic and at least two spare tyres, which were strapped onto the rear. Because there are no rims to be seen, one must assume that the rims were solidly mounted to the rear axle, which means that during the race the tyre had to be fitted and inflated.
The removable wheel rim, which by the way, even after 1920, had to be paid for as an optional extra in the Model-T-Ford, was a blessing. The large amount of unsurfaced roads and the unaffordability of new tyres gave rise to an active system of sending the tyres away to be repaired and then waiting. The standardisation had also not yet asserted itself, so that very often, in the event of a puncture, together with the lack of a spare wheel, it was difficult to provide assistance.
Perhaps the fears of the car drivers back then, are ingrained in the minds of modern day drivers, there are still car owners who are very reluctant to go without the fifth wheel. Whereby, even in trucks nowadays, the statistics show that punctures occur approx. only every ten years, with motor cars the period is even longer. Getting rid of the spare wheel and the extra weight, and obtaining more usable volume, seems to be a lengthy process.
Indeed, the technology for the further usage of flat tyres has been around for some time. With the patent of 1905 and the safety inner-tube from the 1930's, systems with additional air-pockets were appearing. Much later the idea of two tyres was born, each with its own air-volume, mounted on one rim. The slipping of the tyre into the rim well was to be prevented.
In one mechanical solution, there are rings, which compensate for the rim well, after the tyre is mounted, they have however, an external diameter which corresponds to the tyre seating on the wheel rim. Only later were these increased (Michelin, Continental), to provide a support in the event of a puncture or blow-out. However, in general these are not easy to mount.
The safety-aspect suppliers are always interested in emergency systems. Even today, steel discs are attached (with a lot of effort) behind the tyre-flanks, which should prevent the total collapse of the tyre. As a rule, this is sufficient to enable one to carry on driving for a further approx. 80 kms.
The difficult attaching of mechanical aids inside the tyre in the 1980's, was the attempt, through special hump- and rim edge constructions, to prevent the flat tyre from slipping into the rim well. Dunlop's Denovo is, in this case, an important keyword. Of course, one needs new rims and bead constructions which deviate from the current standards.
All in all, none of the new wheel rim constructions has been able to assert itself. This is also the case with the Michelin TRX-system, which also introduced the Whitworth system, and in a number of series is available, at least as an extra. The modern Runflat-tyres are a little more reasonable. They also need other rims, which can however, also accomodate customary tyres.
The Continental-CT concept in the 1990's, showed the most promise. It was a stroke of genius, to have the tyre grip the rim from the outside. This way, no part of the tyre can come into contact with any other part. In the beginning, rings were tightly installed in a complicated assembly next to the tyre beads. Unfortunately this set-up could not assert itself because of the complete re-orientation.
One thing doesn't change, if the rim is so different that it cannot be used with customary tyres, the system will not be widely accepted. Apparently the construction was, in normal driving operation also difficult to master. There are reports of directional instability. There is one Mercedes-model, where this tyre/rim-combination was available as an optional extra.
When it's all said and done, there are three possible solutions: - the self-repairing inside layer, - The difficult to install inner ring (e.g., the PAX-system), - The reinforced sidewall (Runflat).
At the moment it would seem that the Runflat system can assert itself, although the comfort suffers somewhat. However, for a number of years now, the tyres are being made harder and harder and is somewhat compensated through the suspension springing and also rubber buffers. The advantage of the Runflat: One can drive through a motorway road-works without having to worry about blocking the narrowest lane, and one has more usable space in the luggage compartment, e.g., for gas-fuel equipment. 09/10