Designed for an 18" wheel, this tube also works very well for narrow 20" (406) applications. We've used this tube for years in Gran Prix and Stelvio tires on narrow rims. In presta only.
Many guys have gone with this over the years because it seemed to be the only tube narrow enough to handle the 28mm 406 tires. The Continental tubes were too fat even though they stated they were for the Gran Prix. However, the Schwalbe tubes (AV6 & SV6) fit both the Gran Prix and Durano/Stelvio very nicely.