That boat on the A9 ...

[Jess--]

In a previous job we used to tow trailers that were loaded to the limit, due to the nature of the load and various parts having to come off in a certain order it meant that on the trip out the trailers would always be tail heavy but on the trip back would be between 200 & 300kg lighter and nose heavy. all of this meant that the driver had to have a lot of experience towing and specifically towing that rig.

when it started trying to snake (which it did a lot) the simplest way of getting it back in line was to boot the accelerator hard (pulling the trailer straight) and then as soon as it was straight brake hard (usually hard enough to momentarily lock up all 6 trailer wheels) as a result those trailers were among the best maintained I have ever come across.

the owners did try a different tow vehicle (costing around 60k new) but found on the first trip that although it was rated for what was being towed it was lethal if the trailer twitched because of a small delay between the boot hitting the pedal and power actually coming out of the engine (less than 0.25 of a second but it made it almost impossible to pull the trailer straight) so the vehicle was parked up with 26 miles on the clock and left for 5 years (before being used on smaller trailers).

[Mike55]

Something you see in the U.S., but not here is fifth wheels mounted in the back of pickups. I'm fairly sure that they're usually removable. For heavy trailers it's a much safer arrangement as the point where the load is transferred to the towing vehicle is in front of the rear axle.

[ditchcrawler]

1 hour ago, Mike55 said:

Something you see in the U.S., but not here is fifth wheels mounted in the back of pickups. I'm fairly sure that they're usually removable. For heavy trailers it's a much safer arrangement as the point where the load is transferred to the towing vehicle is in front of the rear axle.

I have seen them here. I think you will find that is how the move Horse racing start gates. Landrover did one

[Guest]

1 hour ago, Mike55 said:

Something you see in the U.S., but not here is fifth wheels mounted in the back of pickups. I'm fairly sure that they're usually removable. For heavy trailers it's a much safer arrangement as the point where the load is transferred to the towing vehicle is in front of the rear axle.

Fifth wheelers are more common here than you might think.

 

Just one example of a UK importer.

 

https://www.uk5thwheels.co.uk/american-5th-wheel-trailers-sale-uk?gclid=CjwKCAiA0O7fBRASEiwAYI9QAk7q5IG7x4nFPjJYZvujVIHxm4u-km8fjdbBkiJzeeYKvFwJE2qWohoC7nIQAvD_BwE

 

Edited November 26, 2018 by MJG

[jonathanA]

8 hours ago, Paul C said:

Interestingly (a possible diversion though) the type approval regulations make it a bit worse now. A sensible fitment on some cars is a height-adjustable tow hitch but nowadays both the towbar would need to be type-approved to allow one, and the device itself would need to be.

 

Something like this:

 

Yes always had those type of hitches ( Dixon bate ? ) on my land rovers and just realised I forgot to take it off before parting with my last 110. Also had the advantage that you could have multiple plates with different hitch types fitted. 

 

Its easy tell if a trailer is nose heavy or light when hitching it but the danger is when loading an already hitched trailer.... and very hard to tell it’s nose light just by looking.

[Iain_S]

9 hours ago, Mike the Boilerman said:

(snip)

You seem to be saying here that a negative weight on the towing ball is necessary. I'm inclined to suspect this happens very rarely as it is bloody obvious when trying to hitch up and pushing the trailer hitch downwards to get it onto the ball would surely ring alarm bells for most drivers, so I doubt that happens very often. I suspect the unstable snaking is still perfectly capable of happening when the trailer is 'nose heavy', but just not enough. The thing I found unsatisfactory about the otherwise excellent demo video was they didn't actually tell us the values of the nose weight on the model trailer and car. I also suspect the 'slip' effect you describe on the rear tyres of the towing car is negligible in the case of the small model car in the demo yet the snaking effect is still demonstrated, and varies between stable and unstable with trailer weight distribution. I think there must be another mechanism at play additionally in the model in the video, but I'm still not sure what. 

Not necessarily : the whole thing is dynamic and the trailer, once off line, increases the sideways force on the rear axle of the towing vehicle, increasing the slip angle of the back axle and possibly causing an oversteer condition. In addition, if the weights on the trailer are at the ends rather than the middle, there will be more leverage if/when the trailer pitches, which may well result in a momentary negative nose weight.

 

 

[Paul C]

This is an interesting dog vs pig (Australian terminology) debate:

 

https://practicalmotoring.com.au/car-advice/everything-you-need-to-know-about-towing-heavy-trailers/

 

(Of course, although it relates to Australian towing regs, the laws of physics are the same there - just reversed, obviously).

[rasputin]

has anybody mentioned tyre pressures? 

[Guest]

6 minutes ago, rasputin said:

has anybody mentioned tyre pressures? 

As a cause of creating instability if they decrease rapidly yes.

 

But in the context of getting them correct and where necessery  adjusting them when towing, no, not as far as I can see.

 

But yes it's a valid comment, they do need to be correct both on the tow vehicle and on the trailer.

Edited November 26, 2018 by MJG

[WotEver]

15 hours ago, MJG said:

they do need to be correct both on the tow vehicle and on the trailer.

And the very best way of determining the correct tyre pressures for your car, towing or not, is not to follow the handbook but to use an infrared thermometer. If the centre of the tread is warmer than the outer sides of the tread then they should have a little less pressure. And vica versa. 

[Machpoint005]

34 minutes ago, WotEver said:

And the very best way of determining the correct tyre pressures for your car, towing or not, is not to follow the handbook but to use an infrared thermometer. If the centre of the tread is warmer than the outer sides of the tread then they should have a little less pressure. And vica versa. 

Doesn't that mean you have to drive some distance with incorrect tyre pressures before you can correct them?

[Paul C]

Probably worth looking at historically why Chevrolet set the tyre pressures of the Corvair - they deliberately used a differential in front/rear tyre pressure to tweak the handling characteristics of the car towards a safer balance. So there's more to tyre pressures than just the temperature of the tyre, or the relative wear, etc. 

[Machpoint005]

13 minutes ago, Paul C said:

hey deliberately used a differential in front/rear tyre pressure to tweak the handling characteristics of the car towards a safer balance.

...instead of fitting an anti-roll bar.

[Paul C]

....or the engine at the right end....

[Guest]

1 hour ago, WotEver said:

And the very best way of determining the correct tyre pressures for your car, towing or not, is not to follow the handbook but to use an infrared thermometer. If the centre of the tread is warmer than the outer sides of the tread then they should have a little less pressure. And vica versa. 

Tbh I've never heard of that in 30 odd years of towing, but never had a problem doing it the manufacturers way.

[Machpoint005]

1 hour ago, Paul C said:

....or the engine at the right end....

 

Tell that to a Porsche owner (or an F1 designer).

[MtB]

13 minutes ago, Machpoint005 said:

(or an F1 designer)

 

I'm fairly sure F1 carriages are classed as 'mid-engined', rather than it being at one end or the other...

 

[ditchcrawler]

35 minutes ago, Machpoint005 said:

 

Tell that to a Porsche owner (or an F1 designer).

Never driven one but have been told that some of the Porsche's are exciting to drive!

[bizzard]

16 minutes ago, ditchcrawler said:

Never driven one but have been told that some of the Porsche's are exciting to drive!

Rear engined Porsche 911's and old VW Beetles and Transporters like See-Saws and badly effected by side winds, engine and half the transaxle actuall behind the rear axle, all can suffer badly from over steer.  Not very nice or particularly very safe in my opinion.

[Paul C]

I believe the budget stretched to supplying an anti-roll bar, on the 911.

[bizzard]

12 minutes ago, Paul C said:

I believe the budget stretched to supplying an anti-roll bar, on the 911.

It ammounted to a totally unequal centre of gravity. Fulcrum point way back at the rear. Heavy twin arm torque tube front suspension was fitted in an attempt to balance them up it bit.  

The old 911 suspension height can be altered quite easily though. In fact each whheels ride height can be adjusted.  I altered quite a few for disatisfied cutomers who'd bought them by raising the rear a touch or lowering the front a touch to counteract oversteer. But you have to be careful as by doing this the front wheels caster action alters with it. It was generally best to just stick a heavy weight in the front boot, as most Beetle owners did.

Edited November 27, 2018 by bizzard

[MtB]

Just now, bizzard said:

It ammounted to a totally unequal centre of gravity. Fulcrum point way back at the rear. Heavy twin arm torque tube front suspension was fitted in an attempt to balance them up it bit.

 

Yeah but they look nice, which is the prime consideration when choosing a Porsche.

[rasputin]

and the skoda estelle

[cereal tiller]

25 minutes ago, bizzard said:

It ammounted to a totally unequal centre of gravity. Fulcrum point way back at the rear. Heavy twin arm torque tube front suspension was fitted in an attempt to balance them up it bit.  

The old 911 suspension height can be altered quite easily though. In fact each whheels ride height can be adjusted.  I altered quite a few for disatisfied cutomers who'd bought them by raising the rear a touch or lowering the front a touch to counteract oversteer. But you have to be careful as by doing this the front wheels caster action alters with it. It was generally best to just stick a heavy weight in the front boot, as most Beetle owners did.

And Hillman Imp /Chevrolet Corvair owners ?

[bizzard]

1 minute ago, cereal tiller said:

And Hillman Imp /Chevrolet Corvair owners ?

Yes indeed although the Limp engine was very light all aluminium.