All have inline, 4-cylinder, normally-aspirated four-stroke, double overhead-cam engines and chain drives, and larger generating systems than similar civilian models. C- and P-series Police Specials were also equipped with tires designed to stay on the rim in case of deflation. These run-flat tires, supplied by Dunlop, were able to increase safety significantly by enabling the rider to safely slow to a stop if the tires are damaged in a high-speed pursuit. However, the very thick sidewalls on run-flat tires transmit a much greater level of road shock to the handlebars, increasing rider fatigue; and also generated excess friction/heat which resulted in above average tire wear, prompting operating agencies to migrate to standard high-performance tires. As a result, Dunlop discontinued production of the run-flats. The most popular replacement tires are provided by Metzeler.