Imagine this: you just signed up for a 100-mile Gran Fondo in the heat of the summer months. You've always worn shorts, but you're tired of the sunburn tramp-stamp on your lower back that has made pool parties embarrassing. Enter the Castelli Velocissima Bib, a short that is super lightweight, breathable and, well, a bib, which means you're guaranteed to get through your ride without nature's backhand to your backside.
If you're not opposed to a short, the Louis Garneau Fit Sensor 7.5 short offers a lot more comfort and protection for a lot less overhead. If you definitely want a bib for those longer efforts, the SUGOi RS Pro Bib offers a substantial amount of additional protection, but without the Castelli name.