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Old 03-24-2019, 09:55 AM   #101
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Originally Posted by Gene View Post
Five bikes may not weigh that much compared to the weight of the trailer. Let's say they weigh an average of 30 lbs. each, thus 150 lbs. total. Lets guess the trailer was fairly full and weighed 7,000 lbs. The bikes weigh 2% of the total weight. Even if the trailer was empty and the bikes weighed 40 lbs., the percent isn't that different.

However, I don't know how full the trailer was, how much the bikes weigh and how to calculate the lateral force of the bike weight at the rear of the trailer. That's only part of the analysis. Where are the engineers who understand this?

When we bought our trailers, the hitches had not been set up correctly. Our first was an Equalizer. I think it is a very good hitch, but the dealer didn't care to spend the time to adjust it. Once I did so, it worked a lot better. Our second one did not have enough tension on it when we left the dealer. I experimented and increased the tension substantially and it tows a lot better. I can't remember the name and it is not stamped on it, so I'm guessing it is a Blue Ox. Blue Ox has a pretty good reputation. I think the Equalizer is a better hitch, but it does take some work and a lot of thinking to get it adjusted right if you've never done it before. The hitch is the first place I would look for problems. A suspension shop may be the place to go to get advice on the hitch.

What started the sway that result in a 180? Wind, slippery road, operator error? Are the tires inflated enough? Are the trailer brakes working? What did you do to stop it? Immediately speeding up is one way to straighten a trailer in some circumstances, slowing down gradually is another. Standing on the brakes may aggravate the forces causing sway. Hard braking is the usual response. The skid marks indicate hard braking. It may slow the lateral forces, but not change them. I think once the trailer has rotated enough for the driver to notice, it could be too late to stop the lateral force.

Looking at the photos, it seems you went into the median. Lucky not to turn over and did you cross over to the opposing lanes? The far embankment looks fairly steep.
What's important for stopping sway is the moment of inertia of the trailer pivoting out of control around its axle. The moment of inertia is calculated by multiplying a load by the square of its distance from the center of rotation. So the worst place to put a load is as far from the axle as possible. That said, if you calculate the moment of inertia of the bicycles hanging off the back of the bumper you will see that it has very little effect when compared to the moment of inertia of the much heavier trailer itself.
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Old 03-24-2019, 11:19 AM   #102
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What's important for stopping sway is the moment of inertia of the trailer pivoting out of control around its axle. The moment of inertia is calculated by multiplying a load by the square of its distance from the center of rotation. So the worst place to put a load is as far from the axle as possible. That said, if you calculate the moment of inertia of the bicycles hanging off the back of the bumper you will see that it has very little effect when compared to the moment of inertia of the much heavier trailer itself.
Thanks for explaining it better than me. It must have been those two months in college as an engineering major before I realized the advantage of liberal arts that gave me an inkling of some of the answer.
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