Over the years we have seen a slow but steady increase in the number of trailers being drawn by motorcycles. A number of considerations must be weighed before deciding to pull a trailer behind a bike. These include some simple laws of physics, technical limits of the bike and the trailer and legislative requirements.
In my younger days I was an Ontario Provincial Police motorcycle officer. The following observations are based on an examination of the causes behind numerous bike-with-trailer accidents examined while I was part of a committee of motorcycle manufacturers, insurance, police and transportation officials formulating recommendations on revising outmoded trailer legislation designed for four-wheeled conveyances as it related to motorcycles. Unfortunately, despite our best efforts, nothing has changed in Ontario, or anywhere else as far as I am aware.
If you pull a trailer, this piece is not intended to criticize your choice, but rather inform you of some facts you may not have considered before. The decision remains with you... Caveat emptor, buyer beware!
Simple laws of physics say a wheel tends to maintain balance under rolling motion. Any influence from a side, such as a sudden wind change or encountering a change in the rolling surface, can upset the cart. No motorcycle manufacturer, other than Bombardier with their three-wheel Can-Am, endorses pulling a trailer behind their bikes. Most, if not all, specifically advise against it, usually in their owner’s manuals or in the “fine print,” obviously for liability issues beyond their control. But what is the rationale for this? The following is a summary of the discussions we had in trying to come up with draft bike-with-trailer regulations in the late 1990s.
The brakes on a bike are designed to take into account the fully laden weight of the bike, plus two passengers with luggage. A lot of engineering goes into achieving optimum braking, and BMW has certainly led in this regard over the years with the introduction of disc brakes, ABS, linked brakes, floating rotors and now radial-mounted calipers. Braking efficiency itself, beyond the technical design of the brake system, is dependent on a number of external factors beyond the control of the manufacturer, including ambient moisture on the rotor/pad, temperature, replacement pad composition, rotor/pad wear interface, brake line deterioration, fluid contamination, and so on. All these factors are in the hands of the rider as the bike ages and the environmental conditions to which it is subjected. Suffice to say that beyond that small patch of tire connecting you to terra firma
, your brakes are the most important part of your bike. They are at their optimum when they leave the factory, and it is virtually impossible to improve upon them should you need better braking when attaching a trailer. They are more than adequate for the designed use, but they become woefully inadequate when subjected to uses beyond those for which they are designed. Your stopping distance will be greatly increased!
A motorcycle frame is designed and very extensively tested to provide rigidity where and when needed. Over time we have seen these frames change from heavy, tubular steel construction where the engine was bolted into it, through to the light alloy frames of today which are computer-designed and incorporate the engine as an integral part of the assembly. The goal is to minimize frame flex and best transmit power and braking to the ground, while at the same time save weight and thereby increase fuel economy and performance. The frame is solely designed to accommodate the rider and passenger on top, the panniers on the side, perhaps a light pack on the carrier and a full tank of gas. It is not designed for the stresses from tongue weight, negative tongue weight, or the inertia of pulling or being pushed by a trailer.
In an effort to make the motorcycle track better and make it more responsive, manufacturers have made great strides in the suspension field. Gone are the days when large BMWs had two rear shock absorbers. We now have Telelever and Paralever suspensions, again reducing weight and increasing responsiveness. However, these were never designed for the added stresses from tongue weight or the inertia of pulling or being pushed by a trailer. The net effect is often greatly reduced rear wheel stopping potential due to the rear of the bike often being lifted up, when it is supposed to go down and bite the ground. This can be particularly disconcerting on washboard or gravel because the usual ability of the front brake to do most of the work is now significantly transferred to the rear wheel which, if hopping or skidding, cannot do its job. The end result can be the end of the road.
Have you ever been questioned by your insurer if you pull a trailer with your bike? Likely not. Consider if you do have an accident the insurer will likely have an escape hatch on paying damages because you never declared the fact to them, and moreover the bike manufacturer specifically warns against attaching a trailer. It is your money; consider how you will be spending it.
Of course, few insurance companies would be aware of this, but if it came to paying out a hefty settlement, they would look for anything that wouldminimize their exposure. Again, you roll the dice. You may have coverage, maybe not. Should you ask them the question at the outset? Or carry on and hope all continues to be well?
I am unsure if a manufacturer would try to tie a warranty claim to pulling a trailer. I just know it may provide them a way out for fear it may set a precedent and provide tacit approval for pulling a trailer. They need to always control their exposure to risk from a liability perspective, too.
Here we venture into the unknown. We have all seen trailers of every description, from one-wheel minis to great monstrosities designed as campers for cars up to six feet wide. In between tare homemade frames with a plastic rooftop cargo box, converted whiskey barrels, hot tubs, dog houses, boat carriers with kayaks and canoes 12 feet long. Some are made by legitimate businesses specifically for bikes, while others were never manufactured for bike use, and still others are homemade – more from a novelty than a safety perspective. None have been approved by motorcycle manufacturers, and few provide a hitch specific for a bike.
Lets start by looking at the attachment point to the bike. In my opinion, this often overlooked junction point is the root of all trailer evil. I have yet to see a hitch on the market designed for the potential stresses of motorcycle use. All I have seen are automotive ball and coupling connections with a secondary chain attachment for safety. This crucial attachment system is well proven as adequate for attachment to a four-wheel vehicle, but it is totally inappropriate for two-wheel use.
Let me explain. The design limitations of the vertical ball allows for a very limited rotation of the coupling on the ball, perhaps 15 degrees each way. Once the limit is reached, either one of the trailer wheels will need to lift or the bike will start to lift, depending on the weight in the trailer vs. the weight on the bike. Either way, it can lead to the trailer flipping, or worse, the bike being upended. Another scenario is when for some reason the ball or coupling breaks or disengages. Legislators came up with the simple solution of requiring a secondary chain attachment to keep the trailer from skidding away from the drawing vehicle. Fine for a car, but not for a bike. The chain will allow some turning of the trailer frame, but it will quickly bind and now upend the bike as well. The simple scenario involves a ball simply breaking or a decoupling when not locked down, and the tongue drops down suspended by the chain. As the bike brakes, the trailer tongue will continue with the forward momentum and slide under the rear wheel of the bike, again likely causing the bike to go down.
I have spoken to riders who have addressed this problem with secondary attachments by silver soldering one link together to allow it to break away under stress, thereby defeating the intent of the legislation but avoiding a ticket for no secondary attachment. But the root of the problem has never been fully addressed as far as I am aware. A secondary attachment, as currently required by law, is not a good idea for a bike from the rider’s perspective.
The big BMW that usually pulls a trailer is a fairly wide motorcycle, especially when you consider the total width of the panniers, crash guards and handlebars. This width becomes second nature, but adding the width and length of a trailer takes some getting used to. Less opportunity is available when trying to avoid the suddenly braking car ahead, the suddenly appearing deer in your headlight or the rock on the road. It is easy enough to steer around an obstacle on two wheels, as your track is only inches wide, but when you add a trailer, those inches of width become feet between the two trailer wheels. That four-by-four you so deftly rode around on the bike now comes around to launch your one trailer wheel high into the air, hopefully not binding on the hitch!
Most of the trailers I have seen over the years have been home fabricated or modified for bike use. It seems to be human nature that if there is space, we will fill it. The load is usually nice to have stuff, but it is certainly not necessary stuff. It seems the only test folks do before embarking on a trailer trip is to ensure it pulls and stops okay, but certainly not under emergency conditions. How often have you seen a fully loaded Goldwing or Harley with a grossly overweight mom and pop in the saddle, fully packed down with every convenience one could imagine, pulling an equally overloaded trailer and perhaps a sidecar to boot. Then they pull into a hotel for the night, not camping like most BMW riders. What on earth could they be carrying? Folks, this is simply getting nuts! If you must pull a trailer and a hack at the same time, consider a car. At least you will have air conditioning!
The gross vehicle weight of the trailer determines whether it requires a braking system. Again, this is a regulation written for commercial motor vehicles and automobiles, not motorcycles. I can’t imagine a bike trailer ever reaching the mandatory minimum weight for trailer brakes, but shouldn’t the regulations take the bike/trailer application into consideration? Surely there is a trailer weight tipping point where the two sets of brakes in a bike are simply not up to the task and two more on a trailer would add a measure of safety. This is an area where experts need to chime in and get the ball rolling with the regulators.
Often folks simply bolt on a cheap set of shocks, but like on the bike, shocks can make a big difference. If you pull the trailer empty vs. loaded up, your cheap automotive Wal-Mart shocks will not accommodate the differences and will cause the trailer to hop excessively when empty or not at all when loaded. Ideally, trailer shocks will be quickly adjustable like rear bike shocks. In the world of shocks, you get what you pay for.
Most trailers come with very small diameter wheels. Small wheels are much more susceptible to potholes, curbs and debris. They tend to bounce up rather than roll over like 17–19-inch bike tires. Their bearings need more frequent attention. Again, wheels become a trade-off in trying to keep the body of the trailer as low as possible to the ground. Generally, the larger the wheel, the higher the axle and the higher the payload is situated, resulting in an increased tendency to tip over.
Balance is an important yet often overlooked aspect when attaching a trailer. The more tongue weight, the greater the shock compression and the less free travel for the bike, while negative tongue weight will tend to make the bike lift when braking or even cause the bike to lift off the side stand if loading up. In addition, often the frame ahead of the trailer box is used to carry fuel cans or batteries, all adding to the tongue weight. I have seen trailers weighing more than the bike pulling it, and there is no regulation preventing this! Let us not forget the effect on the front end. Any unanticipated stress on a frame could result in symptoms of “wobble.” Since large BMWs haven’t come with any adjustable steering dampening for decades (remember the old bearing friction damper on the /5s and earlier?), there is no way to tighten down the front end to account for the unexpected when road conditions change without the use of an aftermarket hydraulic damper. Unsolicited plug here: check out this option for any bike that could encounter gravel, sand or mud. They are amazing. You will cut through like a knife through butter without any of that scary edge of the seat feeling. The ones that attach to the headstock are preferred over the hydraulic piston ones as found on small dirt bikes, since they allow on-the-fly adjustments as you encounter different road conditions, especially on a GS.
One Wheel or Two?
It all boils down to your need for capacity. The single-wheel trailer carries much less, but at least it minimizes some of the detriments of a two-wheel trailer. It will track exactly in line with the bike track, it can lean as the bike leans and is by nature almost always balanced along the axle line. The two-wheel trailer allows you to really load up like Granny Clampet, but it will not lean, will take up much more of the lane landscape, has an inherent tendency to tip over when hitting an obstacle, and will have a tendency to drift when turning at speed in S-bends.
Obviously, given the limitations, tendencies and regulations covering them, I am not a fan of pulling a trailer by motorcycle; in fairness, I have no personal experience pulling one. How you ride, what you ride, how you attire and if you pull a trailer are your choices alone. However, this article is in the interest of assisting you in making an informed choice depending on our own risk tolerance and capacity needs. These observations and discussions on using a trailer should help you can make an informed decision. It is possible that if you have never experienced any issues at all pulling a trailer, you are lucky. How long will your luck hold out? Simply stated, motorcycles are not generally designed for pulling trailers. But if you must pull a trailer, the single wheel trailer presents the fewest issues from the choices out there.
If, after considering all aspects of this article, you still want to draw a trailer behind your bike, consider speaking with someone who can design and fabricate a fully articulating 360-degree ball and coupling, where the ball faces horizontally rather than vertically, and lobby your regulators to come up with a legal way to deal with a secondary attachment safely rather than silver soldering for cosmetic reasons.
Hopefully this article will generate discussion on this long overdue topic. Consider discussing this article with your local clubs and speak to your local political representatives to try to raise awareness of the subject. Bike trailers are statistically insignificant in the bigger accident picture, but if you are one of those riders who pulls a trailer, safety is significant. Legislation should protect you, not potentially cause you harm. Trailer manufacturers are concerned about their bottom line. They want to sell product. The choice of attaching a car camper behind a bike is not up to them.
Illustrations are for example purposes, no slight intended.