Is is easier to carry a 25 lb load on a bike with a trailer, or on a bike rack? I’ve got a 16 lb bike kiddie trailer. Putting a 25 lb load in it pulls forward with very little effort, it seems. Is this somehow less effort than not having a trailer hooked up and just strapping the load onto the bike rack above the rear wheel. My first thought was the trailer saves effort because the load weight is on wheels. But the 25 lbs on a bike rack is on wheels, too. Let’s not get into wind resistance and such, I’m just interested in the physics of the weight itself.
It can’t possibly make any difference as far as the weight you are pulling is concerned, whether it is on the trailer or on the bike. And obviously in relation to the former there is also the weight of the trailer itself. In my experience however, having a significant load on the bike does effect pedalling efficiency. If you put a heavy load on the bike, you will sway more, due to being a bit top heavy. That means that with each stroke you are lifting the load on the bike up a little, then dropping it over the other way, then lifting it again with the next stroke. The smoother and less swaying your pedalling action is, the more efficient it is.
My guess is there’d be less rolling resistance with the load on the rack over the rear wheel, mostly because there are fewer moving parts that way. You’d also save the 16 pounds empty weight of the trailer. A slight pressure increase in the rear tire might help offset the weight and keep the tire sidewalls from flexing too much.
Of the sixteen pounds of empty weight from the trailer, about 90%± of it would transfer directly into momentum, the extra 10%± of it of course being tranfered to the ground through the resistance of the tires. While a trailer might be advantageous most anywhere flat, it would behoove you to use panniers in hillier areas.
wishbone, what do you mean about weight “transferring” to momentum or to the ground?
If we assume the simplest models for friction, then it’s only dependent on the normal force (equal to the total weight) and on the surfaces in contact (tire and pavement), not on the distribution or on the amount of area in contact. If we neglect air resistance, then, the only difference would be the weight of the trailer, and it’d be more efficient on the rack. There’s other considerations, though: First off, friction doesn’t exactly obey the simple models (or even the complicated models, for that matter), and depending on the exact situation, it might be larger or smaller for given contact areas. Also, friction isn’t all bad: Rolling friction will slow you down, but static friction between the drive wheel and the ground is necessary for you to propell the bike. This would mean that more weight over the drive wheel could potentially even improve your top speed. We’re also ignoring air resistance, which if I recall correctly is more significant than “solid” friction for a person on a bike.
I disagree. Perhaps there’s some subtleties that I’m missing, but rare is the case when the wheels on a road bike skid during propulsion, as opposed to braking. This could, of course, be changed by adding a significant load to the front wheel or towing it behind. But when skidding (insufficient static friction) does happen, my experience is that it is always shortly after the bike has been stopped, during the initial acceleration phase. I can’t see how putting the weight above the drive wheel would change anything once you are riding at top speed, unless it’s a very bumpy road.
As others have said, the added weight of the trailer results in more rolling resistance. Pulling the trailer may feel easier because the trailer has much less effect on the handling and balance of the bike than a load on the bike. At least with two-wheel trailers, there is no torque (tilt force) transferred to the bike. A loaded bike feels slower because it doesn’t tilt easily, or recover from a tilt easily. It’s possible that balancing a laoded bike takes more work, and overall the trailer might be more efficient in certain situations.