Video – Why Do Some Trailers Tow Stable?

The way a trailer tows makes a big difference in the ownership experience.  So, Why do some trailers tow stable, while others do not?  Even a small trailer that does misbehaves by swaying is rather intimidating on the highway, and a lot of work to tow.  Bigger trailers that waggle are downright dangerous.  (Of course, that does depend on the severity of the waggling.)  Many people call this “Trailer Sway”, or “Fishtailing”.

On a recent trip, I caught one such small trailer waggling away behind the tow vehicle rolling down the highway.  My wife was a great sport and took this video for you.  It’s a little shaky, but, with the help of YouTube stabilization, not too bad.

Learning From Another Example

Look at the trailer and how it tracks behind the tow vehicle.  For the most part it follows well, but when there is an small interruption — like going around this curve, or a bump, a minor steering correction by the driver, etc., the trailer fishtails just a little.

This vehicle caught my attention when the driver changed lanes and the trailer did a pronounced waggle.  Fortunately for them (unfortunately for the video), the driver did not do that again while we watched.  Nevertheless, you can still see some tail wagging in the video as they round this bend.

For reference, this waggling from side to side is called Yaw — one of the important vehicle attitudes.  Important, but not desirable (except in a purposeful full drift!)

This waggle is actually not that bad.  However, I’ll bet the driver feels some weird steering inputs and probably has to fight it just a little from time to time as they drive.  That said, a little can be a lot if it makes the driving more stressful.

Making Trailers Tow Stable

What makes some trailers tow stable, while others waggle down the road?  We wrote a full article about Trailer Stability, (with related trailer design articles) still posted on our parent site  It’s a good place to start reading.

For the one in the video, it’s hard to say exactly the cause of the semi-stable behavior just by looking.  However, I will guess it is poor loading.  Probably the center of mass is too far back leaving insufficient tongue weight.  Also, (not in the video) the trailer tongue is pretty short, which can amplify loading (and stability) issues.  See the post on setting the right axle position with discussion on loading for more on making trailers tow stable.

Of course, there are likely some other contributing factors.  Look at the weight distribution side to side.  Again, this is not a big deal by itself, but the right side motorcycle is bigger, and probably heavier than the left.  (Note the motorcycle rear tire size.  Typically a bigger tire means more HP, and therefore likely more weight, though these are guesses.)  With all that, I’ll bet if they stop and redistribute the trailer contents for a more centered (side to side) and slightly forward center of mass, then this trailer will be much more stable and enjoyable to tow.  While it would be fun to show them on the spot, I’m sure the intrusion would not be welcome.  Oh well.

I will give them props for securing the load well.  As another driver on the road, I really appreciate it when folks take the time to strap down and secure their loads.  Stuff flying from trailers (or vehicles for that matter) is no fun.  Thank You.

Other Contributors In Making Trailers Tow Stable

Other typical contributors (not shown in the video) include wheels, tires, axles, and alignment.  Those are in a section by themselves below.

Aerodynamics can also play a role especially in highway cross winds.  Large profile trailers can get a push by a wind gust, or even by air flow around a larger vehicle on the highway.  Wheelbase also plays a part.  Longer is usually better — if you get the other contributors right.

Finally, the tow vehicle is important – especially when the trailer size exceeds the tow vehicle size.  The bigger the waggle, the more it takes to control it, so make sure your vehicle is good for it.  Too often, the little waggle will  flip the whole system – that’s now where we want to be.  The closer the rear wheels are to the hitch point, the better also.

The key in all of this – It’s never just one thing.  It involves the whole system of car and trailer.  And the smartest way around it is to stack the deck in your favor for stability on the road.

There is so much more information on this topic of trailer sway and stability.  For starters, I highly recommend the article Trailer Sway – Video Review and Discussion.

When It All Goes Wrong

Stability is more than just a buzz word.  As mentioned above, minor instabilities are mostly just an annoyance that make towing less pleasant.  On the other hand, when we think of it as teetering the balance toward disaster, it has a different light.

The example in this article about safety chains is a stark reminder that all the details matter.  It’s never just one thing, it’s the whole of circumstances and situation.  That’s highlighted even more in this article from several news stories about dangling from a bridge by just one trailer chain.  Though I don’t have proof, I suspect weight stability is one of many contributors in both these accidents.  It’s really no joke.  Perhaps both could have been avoided a with setup so the trailers tow stable.

We do have one other article about where and how weight is distributed around the trailer.  I don’t want to insinuate that this is the cause of the accidents in the above articles, but it is the kind of thing that can cause it.  Where you put weight in the trailer makes a huge difference in stability.  And, the longer the trailer, and the taller the trailer, the more important it becomes.

Don’t Forget Wheels And Tires

While it does not appear to be an issue with this trailer, one other factor to help trailers tow stable is the wheels and tires.  Without going into much detail, here are a couple thoughts.

First, tire pressure makes a difference.  One side with low pressure and the other side with high pressure can make the trailer do weird things when you hit a bump or swerve.  So, make sure the tire pressure is right, and the same for all the tires of the trailer.  Tire pressure is also very involved in trailers that bounce.  That’s a different kind of stability, but it relates.

Second, if a trailer wheel is not balanced, or if one gets damaged, like bent, the trailer will wander or exhibit instability – especially at speed.  Have the wheels balanced and inspected once in a while.  It’s a little thing, but it can make a big difference.

Finally, for multi-axle trailers – tandem and triple – make sure the axles are parallel with each other, and perpendicular to the direction of travel.  Straight and square as they like to say.  Misaligned axles will not only cause weird dynamics, the trailers may not tow very stable.  Usually it is a little different kind of instability, but nothing to mess with.  This condition will also wear out tires fast.

For more about tires, read this article about choosing trailer tires, and this about spares.  Enjoy.


Notify of
1 Comment
Inline Feedbacks
View All Comments

We Found These For You . . .

Shop Utility Floor Cart
When there’s a need that doesn’t really fit with existing products, make your own.  That’s it with this new, tough Shop Floor & Utility Cart.  While it’s not monumental in design, it does have some great functionality for DIY’ers, with…

Read The Article

Drill Fixture Zoom In
Oh, I need to drill a bunch of holes, all the same, in 8 parts.  What a pain!  And, I need to cut these other 5 pieces all to match.  What a hassle to measure, mark, and cut each one!…

Read The Article

Aluminum Trailer Tongue Break
What is the first thing you think when looking at this image?  “Oh My !!  That’s Awful.” – was my thought.  According to the driver, “thankfully it didn’t happen when I was on the highway ten minutes prior.”  This catastrophic…

Read The Article

Order Received
This is a Frequent Question about getting the plans, the download, and saving plans after placing an order.  I just bought the plans, now where are they?

Read The Article

Drill Matching Bolt Holes
So many times we need to make matching holes to bolt something on.  You purchased something to mount on your trailer or your workbench or some other project, but now you need the exact

Read The Article

Twisting Trailer Safety Chains
Should you twist trailer safety chains to make them shorter?  Certainly twisting them reduces the length so they don’t drag the ground.  That part is good.  However, there are big issues with twisting safety chains?

Read The Article

Up to 50 Ton Hydraulic Press

Do-It-Yourself Shop Press Plans designed for super high capacity, like 20-50 Ton with a Hydraulic ram or Jack.  Choose these plans for times where perpendicularity and parallelism are important.

NATM Trailer Safety Answers
What do you see wrong with the way the safety chains and other trailer safety equipment are set-up in the image?  That’s the question we asked in the previous article.  The image is a screenshot of a YouTube video by…

Read The Article

4 x 8 2000 lb. Torsion Axle Trailer Plans

For a great trailer in the 4 x 8, 2000 lbs size, these plans are a good place to start.  Lots of options bring great function making these Torsion Axle Trailer Plans right for many situations.

Thread Tapping Straight
A Tap and Die set is a near must for a DIY fab shop.  While the thread creating functions are pretty easy to visualize, sometimes getting the tread to start straight and run true is a different matter.

Read The Article