The notable exception here is Suzuki, which never did fall for the under-seat exhaust on the GSX-R. I had an interesting interview with Suzuki engineers in 2005, who stated categorically that a traditional under-engine exhaust was ideal, though they wouldn’t come right out an accuse their competitors of succumbing to fashion. According to the engineers, a more traditional exhaust was long enough (for an inline-four), could be made considerably lighter, and had sufficient volume when combined with a chamber under the belly to do anything they needed an exhaust to do. Adding weight, far back and high up on the bike, was anathema to the idea of mass centralization, an effort that prompted considerable engineering effort to reduce things like headlight weight and subframe mass. The Suzuki engineers were too polite to openly scoff at their competitors, but the point had been made: under-tail exhaust is dumb, and we’re not doing it.