Cars are designed to carry people and a limited amount of extra weight. Stuffing the trunk with everything you have and the back seat with grandma and the kids will overload the springs and cause the rear to sag and change the handling of the vehicle.
If you had to swerve on the highway to avoid something, chances are you would lose control and end up in the ditch.
Helper springs, extra leafs, air bags. These items can improve the ride height and weight carrying capacity of your vehicle. Just remember that the axles and tires can only take so much. Don't over do it.
Heavy trailers can also cause the rear of your vehicle to sag The weight of the trailer pushes down on the rear and lifts the front of your car / truck, causing a light steering feel and loss of control. If the weight distribution on the trailer is heavy towards the front, special "Weight Distributing" hitches can be installed.
They usually require a heavier hitch frame on the towing vehicle and a pair of bars that have chains on one end to "lift" the whole thing up and level it off. Expect to spend a few hundred dollars.
If you tow heavy, these types of hitches are well worth the money. Without them, your trailer can push you around and can suddenly whip back and forth. All you can do is hang on and hope for the best. I've seen a few go off into the weeds when this happens.
Smaller, lightweight trailers designed to carry a few hundred pounds are a convenient way to increase your trunk space. Toss all the camp gear, coolers, tent, bikes, junk, food, whatever into the thing and off we go!
Did you ever stick your head out the window at 110 kph? (65 mph) Quite a blast, eh?
What about all that stuff back there in the trailer? Is it secure? Did you tarp it?
TARP IT!? Are you NUTS?
Things like life jackets and bags of groceries and clothing will be sucked out of the bottom of a boat at road speeds. Same with the back of a pickup or small trailer. Plastic chairs and kids toys will be the first to jump!
