Run-flat tyres in the 1970s?
Like me, you may have thought that run-flat tyres were a fairly new invention, that became popular with BMW models in the 2000's.
However, while looking through some motoring magazines from the early 1970s I came across two run-flat concepts.
The first was the Dunlop Total Mobility Tyre, later renamed Denovo. According to an article in Modern Motor magazine, August 1973, a blow-out at 160 km/h makes little difference to the vehicle's handling. And you can continue driving on the tyre at speeds up to 80 km/h for at least 160 km before repair is necessary.
The tyre requires a special two-piece wheel rim, which makes repairs simple and tyre levers unnecessary.
These tyres were available as an option on the 1973 Rover P6 3500.
In Modern Motor's July 1974 issue I found an article about a run-flat tyre made by Bridgestone that seems much closer to what current BMW's have.
The Bridgestone Tripguard Safety Tyre does not require a special rim. The tyres were made in two types, one for medium passenger cars, and one for large passenger cars. The medium car tyres had much stronger sidewalls and the latter had a small secondary tyre inside.
The tyres can be driven on at up to 80 km/h for 200 km after a puncture, and the outer tyre can be then repaired like any other tyre.
Like modern BMW's the Tripguard system also included transmitters for each wheel that would notify the driver if any of the tyres' air pressure fell below normal.
Despite the authors of these articles praise and suggestion that these types of tyres would become commonplace, neither of these appears to have enjoyed much success. Even today, and with the support of BMW, run-flat tyres only have a tiny fraction of the tyre market.