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, jpg...@gmail.com 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.

On Sunday, May 9, 2021 at 12:45:22 PM UTC-4, jpg...@gmail.com 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, jpg...@gmail.com 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'

On Sunday, May 9, 2021 at 4:36:41 PM UTC-7, AS wrote:
> On Sunday, May 9, 2021 at 12:45:22 PM UTC-4, jpg...@gmail.com 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, jpg...@gmail.com 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'
Trailers are designed with tandem axles because one axle can't carry the load of the trailer, not to provide greater stability. When turning while pulling a tandem the axles are not aligned with the center of rotation - they can't be because the axles are parallel. The tires want to go in a different direction than the rotation of the turn and must, to some degree, scrub to make the turn. This is why maneuvering them by hand is so difficult. The same thing is happening when being towed but the power of the tow vehicle forces the tires in the direction of the turn. This scrubbing action deteriorates stability, not enhances it.

Tom

The scrubbing action greatlyenhances stability againts swaying.
I have driven my twin-axle Catley trailer for 15 years, and it has been absolutely great, and the stablest trailer I have ever seen.

Le lundi 10 mai 2021 à 07:41:50 UTC+2, 2G a écrit :
> Trailers are designed with tandem axles because one axle can't carry the load of the trailer, not to provide greater stability. When turning while pulling a tandem the axles are not aligned with the center of rotation - they can't be because the axles are parallel. The tires want to go in a different direction than the rotation of the turn and must, to some degree, scrub to make the turn. This is why maneuvering them by hand is so difficult. The same thing is happening when being towed but the power of the tow vehicle forces the tires in the direction of the turn. This scrubbing action deteriorates stability, not enhances it.
>
> Tom

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, jpg...@gmail.com 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, jpg...@gmail.com 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

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, jpg...@gmail.com 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, jpg...@gmail.com 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'

> Trailers are designed with tandem axles because one axle can't carry the load of the trailer, not to provide greater stability. When turning while pulling a tandem the axles are not aligned with the center of rotation - they can't be because the axles are parallel. The tires want to go in a different direction than the rotation of the turn and must, to some degree, scrub to make the turn. This is why maneuvering them by hand is so difficult. The same thing is happening when being towed but the power of the tow vehicle forces the tires in the direction of the turn. This scrubbing action deteriorates stability, not enhances it.
>
> Tom

>> Trailers are designed with tandem axles because one axle can't carry the load of the trailer, not to provide greater stability. <<
I call 'hog-wash' on this one! There are a few trailers by the same manufacturer with the same glider inside in the exactly the same configuration but they have a single axle with larger wheels. The load bearing capability is the the same in both cases. Going to a tandem axle enhances stability (tracking) and allows the whole trailer to sit lower since the wheels on the tandem axle are typically smaller. Lower CoG = more stability.
I completely agree with your point of them being a pain in the butt to man-handle them.

Uli
'AS'

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, jpg...@gmail.com 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, jpg...@gmail.com 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.

On Monday, May 10, 2021 at 11:29:17 AM UTC-4, andy l wrote:
> 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, jpg...@gmail.com 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, jpg...@gmail.com 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.

>> On a road that isn't straight, this pitching oscillation can affect other stability too <<
Please elaborate - I am all ears!

>> Put simply, the first job of the suspension isn't to produce a comfortable ride; it's to keep the wheels on the ground. <<
Agree.

>> With your front wheels off the ground, or even just subject to wild fluctuations of load, your brakes and steering may be impaired. <<
That was a highly dynamic situation persisting for a few seconds only and corrected by letting off the gas pedal to slow down. The road is straight, i..e. no steering or braking was required. The trailer maintained its track behind the vehicle. Since the load inside is distributed symmetrically, no nodding oscillation will influence any of the other axis'.
I still maintain that a tandem axle provides more stability in all directions compared to a single axle and unless you show me the dynamics model to prove otherwise, I think we have beat that horse to death.
Drive carefully.

Uli
'AS'

> I still maintain that a tandem axle provides more stability in all directions compared to a single axle and unless you show me the dynamics model to prove otherwise, I think we have beat that horse to death.
> Drive carefully.
>
This is RAS. The horse isn't beaten to death until it starts to stink and certain folks have the last word.
You (and everybody else) know who you are.

On Monday, May 10, 2021 at 8:23:04 AM UTC-7, AS wrote:
> > Trailers are designed with tandem axles because one axle can't carry the load of the trailer, not to provide greater stability. When turning while pulling a tandem the axles are not aligned with the center of rotation - they can't be because the axles are parallel. The tires want to go in a different direction than the rotation of the turn and must, to some degree, scrub to make the turn. This is why maneuvering them by hand is so difficult. The same thing is happening when being towed but the power of the tow vehicle forces the tires in the direction of the turn. This scrubbing action deteriorates stability, not enhances it.
> >
> > Tom
>
> >> Trailers are designed with tandem axles because one axle can't carry the load of the trailer, not to provide greater stability. <<
> I call 'hog-wash' on this one! There are a few trailers by the same manufacturer with the same glider inside in the exactly the same configuration but they have a single axle with larger wheels. The load bearing capability is the the same in both cases. Going to a tandem axle enhances stability (tracking) and allows the whole trailer to sit lower since the wheels on the tandem axle are typically smaller. Lower CoG = more stability.
> I completely agree with your point of them being a pain in the butt to man-handle them.
>
> Uli
> 'AS'

The tire scrubbing that does occur during turning (no one seems to dispute that as it is obviously true) cannot "enhance" stability; the trailer is literally fighting being turned by the tow vehicle. If this were the case then adding even more axles would make the trailer even more stable. Trailers, or vehicles, with many axles (transporters) articulate the wheels for this reason.

Tom

On 5/16/21 11:14 AM, 2G wrote:
> On Monday, May 10, 2021 at 8:23:04 AM UTC-7, AS wrote:
<Snipperoo...>
>>
>>>> Trailers are designed with tandem axles because one axle can't
>>>> carry the load of the trailer, not to provide greater
>>>> stability. <<
>> I call 'hog-wash' on this one! There are a few trailers by the same
>> manufacturer with the same glider inside in the exactly the same
>> configuration but they have a single axle with larger wheels. The
>> load bearing capability is the the same in both cases. Going to a
>> tandem axle enhances stability (tracking) and allows the whole
>> trailer to sit lower since the wheels on the tandem axle are
>> typically smaller. Lower CoG = more stability. I completely agree
>> with your point of them being a pain in the butt to man-handle
>> them.
>>
>> Uli 'AS'
>
> The tire scrubbing that does occur during turning (no one seems to
> dispute that as it is obviously true) cannot "enhance" stability; the
> trailer is literally fighting being turned by the tow vehicle. If
> this were the case then adding even more axles would make the
> trailer even more stable. Trailers, or vehicles, with many axles
> (transporters) articulate the wheels for this reason.
>

Well, hey - since this thread began with discussing a glider-trailer
towing topic, better into the thread-drift weeds than verge weeds, I
suppose...

I am not a professional trailer designer nor have I played one on
TV...but I've delivered manufacturing-componentry-parts to a dozen (or
so) of 'em in my engineering retirement. I'll bet my retirement slush
fund that multiple reasons exist for quantity-of-axles choices for a
given trailer design, trailer/axle carrying capacities *generally* being
near the top of the list.

As for trailer stability, it'd be difficult to get a more stable trailer
than one with infinite rolling-resistance drag. Or any other kind of
drag, for that matter. I am, of course, assuming that keeping the CG of
any towed trailer behind the towing vehicle while said vehicle is moving
forward, is desirable...

I'll further bet some of my retirement slush fund winnings from above,
that the somewhat-implicit assertion of the final sentence of the above
snippet, is "debatable" (as in, the sweeping claim made, is far from "an
absolute, given, fact") - with the desire for increased stability (or
its lack) *not* being at the top of a designer's list of rationales for
incorporating steerable trailer tires.

YMMV.

Bob W.

We just need an extra crew or autopilot to steer the trailer:
https://youtu.be/xa2ihMkzX3g

I think you've got the base wrong.
Stability is defined as a the resistance of a system to the influence of a disturbance.
If you are driving along with your trailer, a lateral wind gust will push the trailer to the side nd causing it to sway.
Having two axles, the scrubbing of the tires will damp the push to the side - that's the definition of increased stability.

Le dimanche 16 mai 2021 à 19:14:22 UTC+2, 2G a écrit :
> On Monday, May 10, 2021 at 8:23:04 AM UTC-7, AS wrote:
> > > Trailers are designed with tandem axles because one axle can't carry the load of the trailer, not to provide greater stability. When turning while pulling a tandem the axles are not aligned with the center of rotation - they can't be because the axles are parallel. The tires want to go in a different direction than the rotation of the turn and must, to some degree, scrub to make the turn. This is why maneuvering them by hand is so difficult.. The same thing is happening when being towed but the power of the tow vehicle forces the tires in the direction of the turn. This scrubbing action deteriorates stability, not enhances it.
> > >
> > > Tom
> >
> > >> Trailers are designed with tandem axles because one axle can't carry the load of the trailer, not to provide greater stability. <<
> > I call 'hog-wash' on this one! There are a few trailers by the same manufacturer with the same glider inside in the exactly the same configuration but they have a single axle with larger wheels. The load bearing capability is the the same in both cases. Going to a tandem axle enhances stability (tracking) and allows the whole trailer to sit lower since the wheels on the tandem axle are typically smaller. Lower CoG = more stability.
> > I completely agree with your point of them being a pain in the butt to man-handle them.
> >
> > Uli
> > 'AS'
> The tire scrubbing that does occur during turning (no one seems to dispute that as it is obviously true) cannot "enhance" stability; the trailer is literally fighting being turned by the tow vehicle. If this were the case then adding even more axles would make the trailer even more stable. Trailers, or vehicles, with many axles (transporters) articulate the wheels for this reason.
>
> Tom

On Monday, May 17, 2021 at 12:53:51 AM UTC-7, Tango Whisky wrote:
> I think you've got the base wrong.
> Stability is defined as a the resistance of a system to the influence of a disturbance.
> If you are driving along with your trailer, a lateral wind gust will push the trailer to the side nd causing it to sway.
> Having two axles, the scrubbing of the tires will damp the push to the side - that's the definition of increased stability.
> Le dimanche 16 mai 2021 à 19:14:22 UTC+2, 2G a écrit :
> > On Monday, May 10, 2021 at 8:23:04 AM UTC-7, AS wrote:
> > > > Trailers are designed with tandem axles because one axle can't carry the load of the trailer, not to provide greater stability. When turning while pulling a tandem the axles are not aligned with the center of rotation - they can't be because the axles are parallel. The tires want to go in a different direction than the rotation of the turn and must, to some degree, scrub to make the turn. This is why maneuvering them by hand is so difficult. The same thing is happening when being towed but the power of the tow vehicle forces the tires in the direction of the turn. This scrubbing action deteriorates stability, not enhances it.
> > > >
> > > > Tom
> > >
> > > >> Trailers are designed with tandem axles because one axle can't carry the load of the trailer, not to provide greater stability. <<
> > > I call 'hog-wash' on this one! There are a few trailers by the same manufacturer with the same glider inside in the exactly the same configuration but they have a single axle with larger wheels. The load bearing capability is the the same in both cases. Going to a tandem axle enhances stability (tracking) and allows the whole trailer to sit lower since the wheels on the tandem axle are typically smaller. Lower CoG = more stability.
> > > I completely agree with your point of them being a pain in the butt to man-handle them.
> > >
> > > Uli
> > > 'AS'
> > The tire scrubbing that does occur during turning (no one seems to dispute that as it is obviously true) cannot "enhance" stability; the trailer is literally fighting being turned by the tow vehicle. If this were the case then adding even more axles would make the trailer even more stable. Trailers, or vehicles, with many axles (transporters) articulate the wheels for this reason.
> >
> > Tom

Two tires does double the sidewall resistance to rolling. The surface area of a glider trailer (30' x 3') exposed to a side gust, however, is pretty small compared to my travel trailer (33' x 8'). I can tow my glider as fast as the speed limit allows (80 mph in places) w/o roll or yaw stability problems (single axle), but I will slow down to 55 or 60 if it gets gusty while towing the travel trailer. I do tow with large vehicles (F-250 Super Duty), not baby SUVs, which makes a difference.

Tom