A few weeks after getting my scooter, I wanted to buy armored jeans to go along with the armored jacket, gloves and FF helmet.
I ordered a pair from Newenough only to discover that the placement of the knee protection was lining up at mid-shin (completely worthless). I tried on two more pairs at the Cycle Gear store in Allentown, PA. Different brand jeans, same problem.
Figuring it must be some sort of design problem (I think my legs are normal), I went with Icon's Field Armor Knee Protectors:
http://www.newenough.com/armor/elbow_shoulder_knee_worn_on_the_body/icon/field_armor_leg.html
Pros: virtually undetectable under all the jeans I wear, better protection than the "kevlar" no-tear pads found in most "armored" jeans, helps block the wind in the cooler weather, adjustable to fit (most), makes any pair of pants a pair of "riding pants", makes kneeling to take photos (a hobby of mine) virtually painless
Cons: keep you warmer in the warmer weather, something else to put on before going out, velcro straps could be longer for people with more full-figured/muscular calves.
I do feel more confident at speed on the scooter, maybe I am kidding myself, but I figure that a broken leg can be set, but skin grafts would be no fun. The armor itself is hard, but the patting and neoprene are soft.
I don't put them on if I am just jutting across the neighborhood to pick up some takeout or to go to the post office, but if the ride is 15 minutes away and/or involves highway speeds, then yeah, I'm wearin' 'em...
In my experience, it is easier to put these on prior to putting on your pants.
Barring that, it is easier to drop your drawers and put them on your exposed knees than it is to pull your pant legs up high enough to put them on properly (unless you are wearing really loose fitting jeans).
If you do end up pulling your pant legs up to put them on, consider putting your foot up on a chair or a few steps up on a staircase -- that makes is a little easier too.
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Combine with Icon's Field Armor Motorcycle Shorts for as complete protection as you'll likely find...
http://www.newenough.com/protective_apparel/vests_underwear_and_misc_/icon/field_armor_motorcycle_short_2.html