Hard-sided panniers were not evaluated in the tests. Often fitted with hinged drop doors, these have been around for many years. Often gravel would bind or break the hinges, the boxes are bulky, and most designs provided no way to direct the gravel on its way out of the box.
Improved aluminum gravel panniers, featuring a sliding, rather than a hinged door, are available from Wyoming Outdoor Industries, Inc. Similar panniers have been fabricated by other saddle shops. We did not evaluate hard-sided aluminum panniers, but based on reports from some who have used them, the panniers work well and are very sturdy. They are bulkier, noisy (should be lined with some type of fabric to cut down on noise), and are more expensive than fabric gravel bags. The aluminum panniers available from Wyoming Outdoor Industries, Inc., currently cost $395 per set of two, not including rigging. Discounts are available when more than one set is ordered.