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BMW on 01 2nd, 2012 |
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Editorial: On Tires and Compromise
The perfect tire would stick to any surface, never go flat, run in any weather, provide plentiful steering feedback, and wear forever. Fat chance we’ll ever get a perfect tire because a big set of those features are mutually exclusive. So tires are about compromise, compromises between traction and wear, traction and wet performance, traction in hot weather and traction in cold. Oh, and they should generate no noise, no vibrations, nor add any harshness to the ride. Impossible. Tires range from wide and sticky for racing slicks and narrow and hard for low rolling resistance e-mobility specials and then everything in between. Putting the right tire on the car for its intended use, and finding a suitable tire that will minimize NVH, increase fuel economy, and yet deliver appropriate traction in dry and wet/hot and cold is the stuff of nightmares. Once the appropriate set of compromises are reached, the tires reach the public (on suspensions tuned to that specific tire – in the case of high performance and luxury cars). And up until recently, that was five tires per car, then four tires and a donut spare, and even more recently, four run flat tires. The run flat tire allowed manufacturers to save weight by eliminating the spare tire, jack and accessories. The weight savings would help with fuel economy, every pound shed adds up to fractions of MPG – the more weight lost, the more MPG improved – and car makers will take MPG gains wherever they can find them. The manufacturers could accurately claim that the use of run flat tires as improves safety. After all, it is dangerous to change a tire on the side of the road. But they could not claim that they improve feel, that ever elusive notion of road information being transmitted from the contact patch up through suspension bits, and finally emerging in the driver’s fingertips. In addition, they couldn’t deliver the ride comfort expected on a luxury car (and of course the suspensions of cars had to be tuned to deal with the harshness of a run flat). And from an enthusiast’s point of view, they just didn’t feel good. The reason they didn’t feel good was the compromise required in the sidewalls of the tire that provides the run flat capabilities. They are extra stiff/thick to provide...