Purchuased my '03 1800s in '05 as a leftover, and like alot of the other posts here "nothing but the best for my bike" ran 93. Then after the bike had around 1k miles on it I went on a 250mile trip and decided to save $ and run 87. Noticed the bike was running smoother at low speeds, with no loss of power. It also seemed to run cooler, but that could just be my imgination. Since then it has only had 87 in it, and now has 9k miles on it, with no plug problems. Nice to know it was not just me that found this out.