Right, "pedal strike," the pedal hitting the ground. Not a pretty thing. Especially nasty if you're riding a fixie.

"Heel strike" refers to interference between the rider's heel and the pannier. It was a common problem when bike touring became popular in the 1970's when a lot of the equipment wasn't optimized for the purpose. Chain stays were not long enough, luggage racks carried their weight too far forward, and panniers were too rectangular. After that, touring bikes got longer stays, luggage racks were redesigned to hold the weight farther back, and panniers now have a diagonal cut at the lower leading edge.




For what it's worth, here's my Holdsworth "531 Special" on a tour a couple years ago. This is a typical 1970's "race bike" with a short wheel base, and the luggage rack was a typical early 80's Jim Blackburn rack; it was retrofitted to serve as a tourer, I don't know when; so a classic candidate for heel strike. Nonetheless, heel strike was not a problem, owing to the design of the panniers and perhaps helped by my preference for shorter crank arms (165 mm). Here you see it with 650b Col-de-la-vie tires (38 mm). Pedal strike is also not a problem. Nor toeclip overlap, but then again I wasn't using toeclips.