Backpack versus panniers … that’s what I’ve been trying out. Some folks have suggested a trailer; if that works for you, go for it, but there were many dirt, rocky roads I descended with panniers that would have been disastrous with a trailer. Same for some of the mountain descents. Monitor Pass at 50 mph with a trailer? No, thanks. In general when I think of the slowest, heaviest, clumsiest, ugliest vehicles on earth, they are somehow associated with trailers: U-hauls, RVs, semis, logging trucks, hay haulers, boats, shipping containers … I can’t think of any vehicle that anyone ever wanted to speed up or improve handling by hitching on a trailer.
Moreover, trailers invite more junk because they have more space. My goal is less. So on to the discussion of back or pack.
The weight of a backpack loses relevance as an impediment, as far as your back and body are concerned, in relation to its positioning and the surface area/dispersal of the weight being carried. Heavy loads, often much more than the body weight of the carrier, have been managed and moved long distances on the human back for hundreds of thousands of years.
It has been theorized that it was the transportation of heavy stone tools on the backs of the earliest Homo species that exerted a selective pressure on our biomechanics which facilitated the long limb, short torso mechanical efficiency that we exhibit today, in opposition to the bent knee/bent hip locomotor system of Australopithecus. This change in physiology meant that early Homo species could load 15 to 40 percent of their body weight on their backs with almost no net energy cost compared to walking unloaded. We literally evolved for loaded movement.
The basic physiology is simple. The deep muscles of your spine and abdomen are postural. This means their function is to hold and support the weight above your hips, i.e. your head and torso, in a constant upright position during waking hours. Even while sitting, your postural muscles (erector spinae, longissimus, multifidus, transverse abdominals), are at work making sure your upper body does not flop over and fold at the waist. They are some of the most fatigue-resistant muscles in the body whose properties function to rapidly adapt to weight fluctuations occurring above the hips. In conjunction with your spine and lordotic arch, these muscles also help to provide the shock absorption and postural stabilization that protect your head from being jostled around as you walk, run, jump, or fall.
The key for load-bearing is positioning the weight so that it is yoked by, and spread widely across, the scapula and then loaded and compressed down and against the spine keeping the shape of the lumbar arch, thus transmitting and spreading the force directionally across the postural muscles. It’s a common misconception that weight on your back is held up exclusively by the shoulders. In fact, weight hanging on the shoulders pulls backwards and away from the spine; actual weight-bearing is supported by the entire surface area of muscles of the spine, back and abdomen, lower down towards the hips. This is where the bulk of weight-bearing occurs. The shoulders balance the weight and give the straps a place to affix, but the majority of the weight-bearing is done lower down.
This explains why on a bicycle or when hiking, the higher the pack the heavier the sensation and the more easily you tire. It also explains why a poorly adjusted pack that is too high, forcing the load-bearing onto the shoulders and neck, feels so awful. Likewise, it explains why, the lower the pack, the lighter the sensation and the more weight you can carry. So in principle, when properly adjusted and distributed, a pack works wonderfully in conjunction with the lower back to carry loads without tiring out the carrier.
Now consider a weighted bike versus a weighted rider and how that affects the propulsion of the bike. Although the weight is the same whether it is carried on the rider or the bike, acceleration, energy, and handling are affected by the weight’s location.
With acceleration, the mass and the location of that mass make a big difference. Think about the acceleration of two different bike/rider systems, both weighing 320 pounds.
Example 1: 300-lb. rider on a 20-lb. bike. The net weight of bike and rider is 320 lbs., but the downward pressure of the rider’s 300-lb. body mass only has to apply enough force on the moment arm to accelerate a 20-lb. bike.
Example 2: 150-lb. rider attempting to accelerate a 170-lb. bike. The weight in the two systems is the same, but the action of acceleration of the bike and the rider is vastly different. The amount of force the 150-lb. rider needs to apply to the pedals of the 170-lb. bike is much greater than the 300-lb. rider with the 20-lb. bike.
Each object, the rider and the bike, has its own mass and inertia. Changing the distribution of the weight changes how much force is required to accelerate the bike, but it also changes the weight distribution of the the bike/rider system. For the heavy rider the weight is distributed directly above the moment of inertia, and his weight actually facilitates downward force on the pedals. When the bike is weighted, the mass is no longer directly above the moment of inertia, but is now further away from the moment arm, creating a larger moment of inertia, which requires more torque to turn over each pedal stroke. It is much easier to control the acceleration of weight that is attached to your body than weight that is attached to an external object. In plain terms, the lighter the bike, the faster you go and the easier it is to start. This is exactly why, all other things being equal, bike racers go faster with lighter bikes.
With regard to energy, when weight is carried by the rider and not the bike, the energy used to support and move the weight is distributed throughout, and shared by, far more muscle tissue than when the weight is localized onto the bike. When added weight is carried by the rider, the work done to move the weight is transferred to many different muscles in the torso, both fatigue-resistant postural muscles and superficial top support muscles, as well as the hip flexors. Most of these muscles are Type One fibers and use body fat as a primary source of energy, one of the main reasons they resist fatigue.
When sitting on the bike, much of that weight is taken off the far more easily fatigued muscles in the quads and hamstrings. You can easily appreciate this if, while riding seated with a heavy backpack, you stand up on a climb. You will instantly feel the work shift to quads and hamstrings, which are now doing some of the work of bearing the backpack as well as pedaling the bike. Ouch and sit the fuck down.
While seated on a bike you are no longer using your legs to support the weight on your back, and that weight is further taken away from the workload of the postural muscles and shifted off to the bones of the pelvis, specifically the ischium and iliac crest, bones whose wide, slightly arching dimensions were designed specifically to disperse force and carry heavy weight borne above the hips. In other words, your postural muscles and pelvis are designed to disperse weight. It’s why the lower the pack rides, the lighter it feels, and it’s why sitting with a weighted pack is easier than standing.
When the weight is instead allocated to the body of the bike, all of the energy to propel the weight forward and overcome the added mass and inertia of the entire system must be generated by fewer muscles, isolated to the lower body, a/k/a the legs, which, unlike postural muscles, are easily fatigued and rely primarily on glycogen for fuel. From an energy standpoint, delegating the workload to postural muscle tissue that is highly fatigue resistant, oxygenated, and energy efficient, while at the same time decreasing torque demands on muscles in the quads and hamstrings for acceleration over the course of hours will result in the preservation of power and energy in the leg muscles as well as an increase in the speed of the entire system.
Of course once the bike is actually moving you have a whole new consideration, handling. As anyone knows who’s ever ridden a bike on anything other than a straight road, a heavy bike is not your friend.
When extra weight is carried by the rider as opposed to the bike, evolved shock absorbers in the hips and spine, aided by the fascial system, or interstitium, dissipate vibrations naturally throughout the body and direct them towards stabilizers in the hips and lordotic arch, allowing the rider to maintain balance and control of the system with minimal corrective effort. Since the bike carries only the weight of itself, it behaves normally and predictably, with the rider accounting for just a slight change in center as long as the load is below 40 percent of body weight, which postural muscles have evolved to do.
When the weight is carried by the bike, the mass, inertia, and destabilizing changes in force vectors and momentum must instead be actively countered, corrected, and controlled defensively by the rider, as the bike has no stabilizing shock absorbers or counterbalances of its own to maintain control when encountering deviations in terrain. And deviations in terrain are exactly what bicycling is all about: rumble strips, potholes, bumps, gaps, reflectors, cracks, and the normal detritus you have to ride over.
Changing the road surface makes handling even harder. A loaded bike with either panniers or with frame bag/seat bag/handlebar bag is much harder to control when going on unpaved roads, downhill, or between paved and unpaved surfaces. A loaded rider, when encountering these obstacles, will react similarly to a non-loaded rider, with minor adjustments for weight, as the bike’s behavior remains constant and predictable.
Of course there’s a point beyond which the loaded rider begins to handle poorly, too, especially if the pack is heavy and badly adjusted, resulting in a swinging weight relatively high above the center of gravity. This is a matter for each rider, the way they adjust their pack, and how much they carry. In principle, your bike handles a lot better when it’s light.
A loaded bike will react with the force and acceleration of added mass and inertia, will be pulled off balance right or left, launched upwards or sideways, or tip over based on the location of the weight and how it impacts the obstacle. The rider has limited means to control how the laden bike handles obstacles in the road, and is stuck with the primary tool of bike tourists everywhere: going slow.
This was my daily experience while touring the coastal and mountain route from LA to Canada and back. The pannier-laden bike was slow af and handled like a three-legged ox. Leaving aside the speed and handling, the panniers made it impossible to casually lay the bike down or even lean it. You had to constantly ensure that it wasn’t going to fall over with a huge crash and potentially damage the fragile rack, let alone the carbon seat stays.
And when we talk about handling, let’s be sure to talk about what it feels like climbing out of the saddle with a fully loaded donkey bike. It’s fucking awful. The imbalance caused by two leaden parachutes on either side of your bike makes climbing out of the saddle harder than walking a tightrope looped around your nuts. And dog forbid you take the panniers off and try to ride your bike normally. When you have to adjust from donkey bike to unladen frame, you practically have to re-learn how to balance.
All of these handling horrors are but a gentle summer breeze if you’re also unfortunate enough to have front panniers and a tent or other heavy bag on the handlebars. Suddenly you find yourself no longer riding a bike and now piloting a human-powered RV, minus the blender, mini-bar, and teevee.
Handling also sucked balls on anything other than the smoothest of roads, and even then too much bumping would jostle the lower pannier hook loose. These issues you can chalk up to wrong bike, wrong rack, wrong [your whipping boy here], but with a backpack it doesn’t matter what the setup is as long as the pack is low and well adjusted.
This of course is fine. Going slow has a world of benefits, and there’s nothing inherently wrong with dragging around 70 pounds of crap. You never know when you’re going to need a bottom bracket tool, a truing stand, and a rock collection all on the same day.
Likewise, a pack of any size is anathema to many people. In simple terms, they find anything on their back unpleasant and tiring. For others, there’s a contradiction in having a beast of burden and then putting any part of the load on yourself, to which I say, ride as you see fit. If you want to go faster, moving the weight onto your back will do that. It may make riding totally miserable; it certainly hasn’t for me. What makes riding miserable for me isn’t a little extra work or discomfort. It’s averaging 7 mph over a ten-hour day.
That is misery.
And by the way, don’t scoff at the speed. Unlike the fake bike computers that measure “moving time” (can one of you physics-inclined folks explain to me what “stopped time” is?), I calculate speed the old-fashioned way: Take the distance, divide it by how long it took me to get from Point A to Point B, and that’s my speed. One-hour lunch break? Oh, well. Flat tar? Oh, well. Shutter moment overlooking a gorge? Oh, well.
Combine a true mph with long hours and big miles and suddenly how fast the bike goes really matters. Three or four mph over 10 hours is massive, and if I can get that with no net increase in exhaustion, well, I’ll take it.
Which isn’t to say that a heavy pack doesn’t eventually result in tired back muscles. But guess what? Riding a donkey bike for ten hours eventually results in tired leg muscles. The difference is that one goes faster, handles better, requires less equipment, militates towards carrying less junk, and allows you to ride a wider variety of surfaces at different speeds. And don’t even get me started about changing a flat with fully loaded panniers.
Best of all, the fatigue in the shoulders, neck, and lower back goes away minutes after the pack comes off, and they are fresh as a daisy the following day. Wish I could say that for my legs when pedaling the donkey.
Nothing is perfect, of course. A heavy pack presses down on your crotch, and for some people that’s a deal-breaker. However, people have been using the bugaboo of erectile dysfunction for decades as a reason to scare men away from cycling, and until I see a peer-reviewed, double-blind, randomized clinical trial showing that cycling with a heavy pack takes the lead out of my pencil, I’m not buying any of it. I still remember back in the 80s when some quack announced that riding bikes would put paid to your sex life. Thousands of men quit riding; I had three kids.
To date I’ve only got about 500 miles of riding with a loaded pack. That’s not much, and it’s not conclusive, either. The older I get, the less bearable it may become. More realistically, what works in and around town may not work at all when cross-town becomes cross-country.
But what’s the fun of riding if you can’t figure things out for yourself?