Outfitting a recumbent for rough roads and gravel trails is the same as on a regular bike:  add more aggressive tires.  Most recumbent ship with relatively smooth tires, best suited to roads and paved trails.  In order to ride safely on gravel and bumpy roads, you’ll have to switch those slick tires for something with a little more bite.  If you visit a bike shop, they will be able to choose the best tire for you, based on where you intend to ride.  Department stores that sell bikes usually have a small selection of tires as well, but don’t expect the staff to be nearly as helpful.

In addition to new tires, you may also want to add a set of fenders.  The fenders will prevent dirt and rocks from being thrown at you, and your bike’s frame.

When riding on loose gravel or crushed limestone trails on a two-wheel recumbent, there are a few things you should be aware of.  First of all, it’s not quite as easy as on a regular bike.  Don’t make any sudden course corrections until you’re used to how the bike handles on loose ground.  When passing through gravel, maintain a straight path until you’re on more solid ground.  Of course, if you ride a trike, you can do almost anything you want.  ;)