Sierra Nevada Airstreams -|- Owner's Guide

Enjoyment of the whispering winds, the zephyrs, the airstreams of the Sierra Nevada and Great Basin areas of the United States in a recreational vehicle.

The physics of RV motion

Gravity - Newton - Secure - Sway - Tracking - Wind - Heat -

Most RV's are big heavy things that are hard to get moving, hard to stop, and hard to see around. What does this mean to the driver?

Any time you want to take your house with you, you have to consider extra weight and storage in your travels. Even the minimalist - the backpacker - has to consider what to take and what to leave behind; how the equipment will impact ability to travel; and how the equipment will affect safety in travel.

When you decide that the comforts provided by an RV are a benefit on your outings instead of, or perhaps as a supplement to, backpacking, you will experience a travel experience different in many ways from a daily work commute.

Gravity and other loads

The first consideration in an RV is being able to hold all your stuff in some kind of container that won't collapse or break apart as you are traveling. This means that the RV has to be a stout box with running gear and tires designed to handle the load. It isn't going to handle like a sports car much less your typical commute vehicle. Drivers should make sure that they adjust their expectations, perceptions, and judgments to accommodate their vehicle for safe driving.

Newton's laws of motion

However something is moving now is how it is going to continue to move unless you push on it. And when you push on it, it is the same as if it is pushing on you. These basic laws of motion can be used to gain insight into why your RV behaves the way it does. It takes a lot of effort to get your rig moving and a lot of effort to get it to stop. This means the RV driver needs to pay careful attention to traffic and allow more room for maneuvering.

Inertia, mass, and size all comes into play in your RV driving experience in terms of whether the horse is controlling the cart or the cart is controlling the horse. When a trailer starts to weigh more than the tow vehicle or starts to be larger than the tow vehicle, more attention needs to be paid to making sure that the horse will stay in control. This is done by adding controls to the trailer (e.g. brakes), adding control to the hitch point, and choosing equipment designed for the task at hand.

Secure that load!

It is so easy to just toss it in the back seat. And most of the time it is no big deal. But you need to consider the "What ifs." What if something started sliding around as you were going around a corner, starting up from a stop, or hitting the brakes hard to avoid the idiot who cut in front of you? What if, Lord forbid, there was an accident and your rig rolled over or collided with something?

Secure your load. Make sure that, at the very least, you have objects in both your trailer or tow vehicle placed so they will not shift position or fall off shelves or couches during normal driving. Keep stuff stowed. If you can, try to stow stuff so that it would stay put even if the rig was turned upside down or stopped very very suddenly.

One source of injury in accidents is the result of internal body organs stopping against other parts of the body after the body has been stopped by seat belts, air bags, or other car parts. If this is what your soft parts can do, think about what things in your rig can do as they try to find something to stop them after a collision.

Up and Down and Side to Side

Trailer towing really means you have two vehicles coupled in the middle. Each will want to do its own thing and the coupling between the two determines how they 'talk' to each other to determine who is in control. The driver needs to be aware of both up and down movement as well as side to side swaying. It is a good idea to do everything you can to avoid any quick maneuvers so that you can safely control your rig.

Spring bars on the hitch assembly are the first weapon in controlling up and down movements. These bars fight droop at the hitch point and, as a result, spread the weight of the hitch point to all vehicle and trailer tires. This means that you can load your trailer so that 10% to 15% of its weight is on the hitch (the rest is on the trailer axles). The spring or load leveling bars will spread this weight so that the front steering wheels won't be lifted off the ground and the rear wheels do not take on excessive weight. This load leveling effect can help keep weight on traction and steering tires on rough roads.

See the page on sway control for more about trailer sway and its cures. If your rig is properly configured and loaded it should normally exhibit little or no side to side sway. This means your two vehicle is strong enough to carry the load, the trailer is not overloaded, both the tow vehicle and trailer loads are properly distributed, and the hitch is at the right height . Sway control should be an insurance against abnormal situations and not a requirement for routine travels.


If you are behind a big rig you may see signs about wide turns. The driver of that rig has to move the tractor so that his trailer doesn't run over curbs or, perhaps, cars in an adjacent lane. You need to also keep in mind that fact that your trailer may not track your tow vehicle. And, since the trailer wheels are in the middle of the trailer, you also need to watch out for a rear end that can swing out of the track. Taking a tight turn out of a gas station can be a good way for trailer bumper to try to take out a gas pump.

When maneuvering in tight spots, go slow and keep a sharp eye on all corners of your rig. See the section on spotters in the backing article.

The wind

Trying to get air from one side of your rig to the other and on its way is not an easy task. The air getting from the front to the back of your rig while going on down the road is the case most studied because this drag is perhaps the second most important factor in fuel consumption. (The first is your tow rig engine, gearing, and style configuration. Load weight takes a distant third place). But air does more than just provide drag. A cross wind on the North California coast has pulled the siding off a trailer. Racing cars use lift of air flow to pull the car down on the tires.

The driver may sometimes need to consider whether driving with a tail wind or head wind when thinking about fuel stops. A stiff head wind on a long grade can seriously reduce distance traveled on a tank of gas. Reducing speed may help but this will depend upon the rig. An 81 suburban (454, 4.10) seems to run between 6 and 8 miles per gallon (mpg) so speed isn't too much of an issue. Some new diesel rigs can between 12 and 18 mpg towing so speed can be a bit more important in fuel economy considerations.

A second consideration for the driver is rapidly changing wind from the sides. This may be from storm gusts or it may be the air trying to get out of the way of a passing big rig. These winds will shove the rig around on the road and that requires careful driver attention to keep control in hand.

See some formulas and graphs in Rainer Pivit's article -

A picture of air flow -


It is all about heat. The engine in your RV burns fuel and what doesn't go into moving the vehicle goes into heat that is dissipated by the radiator. The energy required to move the vehicle goes into overcoming friction from air resistance, bearings, and tires and that also results in heat. When you slow down, the brakes may also contribute to the friction causing them to dissipate heat. The need to control heat is a major factor influencing the design of your tow vehicle.

When there are large loads, such as towing a trailer up a hill, or the ability to move heat away from the vehicle is restricted as in heavy stop and go traffic, the driver needs to keep an eye on engine and transmission temperatures so they don't cause failure. If things start to get hot, get off the road and find a means to help cool things down.

Precautions also need to be taken when going down hill. Minor hills only need air and rolling resistance. Significant hills may also require using the engine as a compressor. Severe hills require using brakes. It is not a good idea to use brakes for more than a few seconds at a time so severe hills will need the driver to take extra effort to shift braking to the engine by using lower gears and by using speed variations and rest stops to keep the brakes from overheating.

disclaimer - owner's guide - -

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Last updated 02/16/2012