You are a hefty guy, say 300 pounds, and your brother-in-law, who has the annoying habit of calling you "little fella," is coming to town and you have promised to take him for a short ride on your new ThunderScoot 1900. You figure with old Tiny on the back, you will be carrying about your own weight more than you are supposed to. What's going to happen if you take him around a couple of blocks and come right back? Frankly, your biggest concern is going to be that, with all that muscle or blubber perched on the back, your bike is going to be a real handful to ride, especially at low speeds. If he gets antsy back there, you may have to fight the bike the whole way. Pulling out of the driveway might be more excitement than you want. Assuming you have the specified pressures in your tires and the rest of the bike is properly maintained and that you can keep your bike upright, little besides the compression bumpers on your rear shocks are going to bear any scars from Mr. Tiny's Wild Ride. Your tires won't have a chance to build up much heat in a four-block ride at modest speeds. However, if you agree to deliver his 250-pound sister (and luggage) to a location 700 miles away, and plan to make it in eight hours running on poorly maintained back roads with the mercury hovering just over 100 degrees, you may not get there.