On Monday, 10 May 2021 at 16:13:12 UTC+1, AS wrote:
On Monday, May 10, 2021 at 7:39:34 AM UTC-4, andy l wrote:
On Monday, 10 May 2021 at 00:36:41 UTC+1, AS wrote:
On Sunday, May 9, 2021 at 12:45:22 PM UTC-4, wrote:
On Sunday, 9 May 2021 at 17:16:47 UTC+1, andy l wrote:
On Sunday, 9 May 2021 at 16:25:16 UTC+1, Craig Reinholt wrote:
On Saturday, May 8, 2021 at 11:13:01 AM UTC-7, wrote:
On Saturday, 8 May 2021 at 16:22:17 UTC+1, Robert Seccombe BE wrote:
On our single axle two place glider trailer I destroyed the two original tires that were on it when I acquired it. One was just a cut in the sidewall that I discovered while parked. The other was a total failure while on the highway; and I wasn't aware of it but for another driver alerting me. The tire was completely missing and the rim was destroyed; this while towing behind a 21' class C. The replacement wheel and tire were from W&W. Though it does seem to tow somewhat better with the newer tires, I have never been happy with the way this trailer tows and I am seriously considering adding a second axle. The Airforce Duo Discus trailers are duel axle..
Having had previous experience of one trailer losing a wheel and another having a dramatic tyre destruction, when we got a Duo with a Cobra trailer I over-ruled advice from Cobra and insisted on specifying the dual axle option. I came to regret this, partly because of the difficulty in hand manoeuvring it but mainly because the trailer, having a level it wanted to maintain that was not what the vehicle hitch wanted, tended to nod during towing. Keeping the front axle tyres a little less inflated than the rear ones helped but did not eliminate this. It may have been more comfortable if the tow car did not have self-levelling suspension but I sold out of the glider before I sold the car.
Add 30 + lbs to the nose of your glider trailer and see how it tows. It may fix your sway issues.
Craig
I didn't think John was talking about the trailer swaying.

I entirely agree with him. With two axles, uneven roads create a pitching moment on the trailer. Looking in the mirror, one can see the front bouncing up and down, sometimes an inch or more, and if this is relative to the car it means something is bending. Further, if the pitching is happening on a road that isn't straight, it means it could be adding unstable inputs in the yaw direction too.

So although some under-confident folks might think a twin axle trailer is more directionality stable, I'm not convinced, and there's certainly not enough benefit to make up for the drawbacks

On the worse ridged motorway I've driven on, the D1 from Prague towards Brno a few years ago. the pitching was so bad, shaking my head up and down, that I drove at 40 mph for a while, then turned off and took a different route towards Vienna. Then I avoided the road for a few years until I read it had had some work done - not fully resurfaced but planed down flat again.

The only advantage of twin axle over single is that if you have a puncture you can continue a bit to a better place to change the wheel, as for instance when I noticed a trail of sparks in the mirror while driving through road works contraflow, and carried on to the next services.
That's correct Andy, that is exactly what I experienced - especially over ridged or concrete sectional motorway.
We must be talking about two different tandem axle trailers here. ;-)
I have a Cobra tandem axle trailer with the original tires (175/70R14), which I run at the max. permissible pressure. For the last five years, I have made an annual trip from South Carolina to Moriarty, NM and back. That is roughly 1,500 miles (2,400km) one way, so I have accumulated roughly 15,000 miles (24,000km) on that route alone. The road conditions are not always the best and in some instances, one could have easily fried an egg on the highway's surface. The only difficult stretch is the elevated part of I-55 east of Memphis, TN, where the segmented concrete bridge is sagging in the middle of each segment. This will excite a severe nodding action, which can only be countered by slowing down to below 35mph. Even the 18-wheelers do that on this stretch. For the rest of the trip, the trailer is rock-solid around all three axis', i.e. it has zero tendency to either nod, rock left to right or fish-tail!
One big influence on the overall behavior of the trailer is what's in it and how the load is distributed. In my case, the heaviest part - the wing's center panel weighing in at 220# (100kg) - is located a few cm above the floor and centered over the axles. The wings have an aspect ratio of 25, so they are not very tall when placed leading edge down. The fuselage straddles the center panel just a few cm above it. The trailer is has an Aluminum top. With all that, I would venture to say that the CG is fairly low compared to other trailers. Also, in my case, the axle track (width from wheel flange to flange) is very wide compared to other trailers, which has to have a further stabilizing effect.
Another big influence on the trailer's stability is the type of vehicle towing it. I don't want to (re-)start a thread on this (there are several on RAS) but I am towing with a full-size Ford E150 van, which in itself is a heavy and very stable rear-wheel drive vehicle. I towed my trailer once with my VW Passat SW a short distance and although the trailer has well functioning and maintained brakes, I would not do that ever again. I wasn't sure who was actually in charge!
In summary, not all tandem axle trailers are the same and comparable. There are just too many variables in this equation.

Uli
'AS'
It's a little odd that you express scepticism about what John and I said, but then give an example of exactly the same thing happening with the same type of trailer in exactly the same circumstance, an uneven concrete surface
You mean the severe nodding motion I described? I think you misunderstood.. The road surface on that stretch of highway is level left to right but has long waves in the order of maybe the length of the whole rig. When the towing vehicle is dipping down into the 'valley', the trailer is still about to crest the 'peak'. This excites a severe up and down oscillation. The first time I went over this stretch of I-55, the front wheels of my van came off the road. Even 18-wheelers are transitioning this stretch with their hazard flashers on at 35mph.

Uli
'AS'

No, I think you misunderstood. That is exactly what John and I were talking about

Your further elaboration only confirms something else I already said. On a road that isn't straight, this pitching oscillation can affect other stability too. Put simply, the first job of the suspension isn't to produce a comfortable ride; it's to keep the wheels on the ground. With your front wheels off the ground, or even just subject to wild fluctuations of load, your brakes and steering may be impaired.