So Long Way Round has inspired you, and you want to explore the world on an adventure bike. You're also 5 foot 6 inches tall and can't touch the ground while sitting on the BMW R 1250 GS of your dreams. Should you give up your dreams and settle for a Honda Rebel? No way. The Rebel is a good bike, but just because you are vertically challenged doesn't mean you have to settle for riding a beginner bike for the rest of your life. There are ways to make a tall bike work for you even if you're not Andre the Giant.
It's worth pointing out that although being small in stature is the one area of motorcycling where women far outnumber men, these tips apply equally to men, women, or whatever gender you identify as. All that matters is your height, your weight, and setting up the bike to work best for you.
Improve Your Technique
There are still ways you can ride an unmodified tall bike. Jocelin Snow is 5 foot 1.5 inches tall (that half is important when you're of smaller stature). Yet she rides even the largest BMW adventure bikes despite having a full six inches between her feet and the ground when seated normally. Check out this video to see how she does it. Then check out this one to see her rolling starts and stops. I'm super impressed.
Even at six feet tall, I can't flat-foot my Kawasaki KLR 650. Holding it up at a stop on my tippy-toes is possible, but not optimal. A better technique is to lean a little to the left and let my left foot go flat. This is actually much more stable than tip-toeing both feet, despite using them both. It also allows your right foot to remain on the rear brake, which is handy for holding yourself in place when stopped on a hill. I've been getting better at this technique while recovering from my broken right foot since I'd rather trust my undamaged left foot to hold up the weight at this point.
Most modern motorcycles have an adjustable suspension. If yours doesn't, an aftermarket option probably does. Some people never touch their stock suspension settings, which gives up an important method of tuning not only performance but also ride height.
From the factory, most suspensions are set to accommodate a 180-pound rider. Smaller people usually weigh less, so you'll want to soften your suspension to match your weight. The suspension is designed to work best while you're sitting on the bike. It sits tall when parked, then hunkers down to the appropriate height and geometry when you get on. If it's set up for a 180-pound rider and you only weigh 120, it's not compressing enough and riding taller than it should be. Setting it up correctly will also improve the bike's overall performance since it will now operate as the factory intended.
Lower The Seat
A few bikes, like the Honda Africa Twin, offer multiple seat height positions. All of us, though, have the option of getting an aftermarket seat that lets you sit lower on the bike. You may lose a little padding, but if you're small and light you don't need as much cushion as a larger, heavier rider.
The other factor to consider is seat width. A slightly narrower seat can give you a big advantage when it comes to getting your feet down to the ground. You won't have to spread your legs as wide to get them around the seat, and that advantage translates into farther you can reach down to the ground.
If you're feeling bold, you can modify your existing seat yourself. Remove the outer cover, carve away at the foam, then stretch and reattach the cover. I'm on taller side, but I've done this myself for a Mazda Miata seat—ironically because I sat too tall to get my head below the roll bar for track days. I found an electric carving knife to work particularly well for this task. Just don't plan on using it for Thanksgiving dinner afterward.
Lower The Bike
Note that lowering the bike itself is the last option on this list. If you can make the bike work for you using any combination of the above methods, do that before lowering the bike. The suspension is designed to work in a specific geometry, and dropping the bike will alter that, affecting your handling as well as lean angle and suspension travel.
With the single rear shock suspension common on modern motorcycles, the easiest way to reduce your ride height is by replacing the linkage connecting the bottom of your shock absorber to the bike. This is known as the "dog bone" because it's shaped like one. A small change in the length of the dog bone will have a large effect on the ride height, as well as the spring rate. Dropping the bike may stiffen the suspension. You may be able to dial this stiffness out, or you may not, depending on the bike.
Another option is to shorten the rear shock absorber. This involved either having your existing one modified, or finding an aftermarket one that's shorter than stock. Either option is much more expensive than replacing the dog bone. The advantage is that you can keep your stock spring, or at least a reasonable spring rate.
In any case, it's best to research lowering options for your particular make and model to learn what proven solutions exist, as well as pitfalls to watch out for.