The Independent American Magazine for all Mini Owners
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Run-Flats: I By Peter D. DuPre Photos by Bridgestone and the author don’t know about you, but I can’t think of a good time or place in which to have a blowout or a flat tire. Sure, some days and places are better than others. If a flat is to be my Karma, then I would rather it happen on a straight stretch of country road that is blessed with wide shoulders. The weather should be sunny, not too hot and I would be wearing jeans and a T-shirt. In my experience, however, you are much more likely to have a tire problem while on the freeway at rush hour, or when it is pouring with rain, at night and you and your spouse are dressed for a night on the town. That’s how life happens and that’s why I like the idea of a run-flat tire or RFT. What I don’t like about them, however, is the reality. First, A Little History When Goodyear first pioneered the very first run-flat tire, which they called a self-supporting tire (SST) back in 1978, I was hopeful that my days of dealing with flat tires would shortly be coming to an end. The early SSTs were promising but as they say, there was a lot of low-hanging fruit to be picked first and it wasn’t until the 1997 Corvette debuted with new Goodyear EMT run-flat type tires that a viable commercial product was available. The Goodyear tires ran on standard design wheels and used reinforced sidewalls to support the weight of the car on the flat tire without completely collapsing. It meant that you could drive at a slow speed on a flat tire, eliminating the need to carry a spare. On the Corvette, this was an especially attractive idea, as the famous sports car has very limited stowage space and the elimination of the weight of 34 MC2 Magazine www.mc2magazine.com the extra wheel/tire, jack and wheel wrench helped improve both performance and fuel economy. At about the same time the French tire maker, Michelin, brought out their PAV tire, which is short for “Pneu accrochange vertical” and is roughly translated as Vertical Anchorage Tire because of the way the tire bead sealed onto the specially designed wheel rim. The company later changed the name from PAV to PAX, and in conjunction with special wheels and unique sealing around the bead, the PAX tire also used a hard rubber support ring around the wheel to support the weight on the flat tire. Later, in order to reduce unsprung weight, the support ring incorporated a mixture of rubber and polyurethane, along with a tire pressure monitoring system. The advantage to the PAX tire is that it allows the vehicle to be driven at a higher speed (still reduced from freeway speeds) without compromising vehicle handling. In the intervening years between these developments, Goodyear and Michelin have agreed to work on run-flat technology, as have Bridgestone and Continental. Likewise, Pirelli has been working on their own PAX-type tire. Because of the fact that the typical stiff-walled run-flat can be driven at speeds of up to 55 mph and for as long as about 50 miles without any noticeable affect on handling, and because while doing so the motorist may have no idea that a flat has occurred, the federal government has mandated that TPMS (or tire pressure monitoring systems) be standard equipment on all cars beginning with the 2007 model year. TPMS has been developed along with the run- flat technology and is generally accepted as a great way to A l t h o u gh t don ’ hk t l i y wh ee t orem a k a s a d n v er t d don ’ i s ae nd t t t w , mh o s t d r em . iv er s The Tires Everyone Hates