Tow weight of 26M heavily laden for remote area cruise

[bartmac]

Too low a tongue weight is probably as dangerous as too heavy.....the instability low tongue weight induces makes the whole rig uncontrollable....been there and done it...not towing a Mac but a large trailer with building materials loaded by forklift...incorrectly too far back on the trailer.Also the tongue weight is NOT influenced by the number of axles....as far as I understand the situation.Different jurisdictions will have different rules as to the max weight allowable behind different vehicles....BUT the BIG thing about Mac's is they are all heavier than most people think....part of the marketing ploy of the Macgregor corporation.....basically the standard setup of a Mac on trailer in Australia is only just legal... but fitted out with only the most basic requirements makes it illegal and requires a larger vehicle to tow it.Not sure of insurance rules in other countries but in Oz if you break a rule/reg your insurance company as the right to not pay...than includes overloading....vehicles and trailers

[RobertB]

Two responses

possibly there is some misunderstanding of your local regulations, it's hard to imagine a goverment would intentionally wish to harm it's citizens with grossly unsafe regulations such as limiting a tonque wieght to 150 pounds regardless of GVW.I would reccomend checking with some businesses that tow commercially and see what their interperatation of the regulation is.

:
Ray, I have a European car, a Volvo XC70. This car is one of the main tow vehicles for families in northern Europe. It is rated at about 3300 pounds tow weight with a max tongue of about 150 pounds. This works out to about 5% tongue load. Here in the USA and commonly on this board, it is pretty universally accepted that 10% is the safe value. I really believe that if this car were originally sold/rated in the USA, the rated values would be different. I believe it is due to how the local regulations work into the math of determining towing capacities. It may also be due to the allowable design of the trailers. I have towed with this car at the 10% value with a single axle, keeping internal load to a minimum (and my speed down), and felt very safe.

Also the tonque weight is NOT influenced by the number of axles....as far as I understand the situation.

Bartmac,
SeaHouse and I have been around the block a couple of times on this issue - not sure if we have ever come to a consensus but to the best of my understanding, the following is the best I can offer.
Adding a second axle where the axles are centered around the original axle will not change the center of lift/tongue loading - IF a tandem axle setup is used. If one uses two independent torsion axles, the result is moving a discrete point of lift/support forward (about 18 inches) and this definitely reduces the tongue weight. This is how I added an axle and the results were definitely a lower tongue loading.

[bartmac]

Sorry....probably talking at cross purposes...I came from an assumption the axle group is movable/slideable...all our trailer yachts in the past have had sliding axle mounts ie along the chassis to tune the tongue weight

[RobertB]

Bartmac - I understand, you are doing it the traditional way. Those of use too cheap to replace the whole setup and just buy a second axle have created a different situation.

[raycarlson]

I added a second UFP axle so as both axles were centered on the original axle location, I noticed no dramatic difference in tonque weight, I keep it at 7% or three hundred pounds.

[RobertB]

I added a second UFP axle so as both axles were centered on the original axle location, I noticed no dramatic difference in tonque weight, I keep it at 7% or three hundred pounds.

I wonder if your tow ball is higher than mine? This would move the center of lift aft a bit (unload the front axle).

[kurz]

bartmac wrote:Also the tonque weight is NOT influenced by the number of axles....as far as I understand the situation.


I dont think that this is completely true.

If you have just one axle it is easy to weight the tongue weight.
If you have 2 axles the tongue weight will change. It depends of the position of your coupler at your car. Is it VERY deep mounted (station car), the tow weight will be less. If it is very HIGH mountet (like trucks...) the tow weight will be higher.

the reason is that the front axle will be more or less pressed down.

you can test this very easily by weighting in different positions, higher and lower!

[Tomfoolery]

That's true for independent (torsion, usually) axles, and depends also on the stiffness of the suspension. Using 3500 lb suspension on each axle for a 4000 lb total wheel load means the spring rate is high for the load, making it all the more sensitive to ball height and bump in the road size than if the spring rate was adjusted to better suit the actual load each axle supports.

Equalized leaf spring suspension will not vary in any appreciable way with ball height other than the CG of the boat/trailer combo moving back/forward as you lower/raise (respectively) the ball, which will change the tongue load a little.

[bartmac]

Probably should have explained.....the use of independent springing is not that common yet in Australia....mostly what we would call load sharing ie a pivot between the two springs thus centreing the weight and minimising the effect on tongue weight.....pictures I've seen off just adding an axle behind the existing axle on a Mac trailer is really only a half job...I guess better than nothing.Then again the mod I'm doing at the moment staying with single axle(5200 Lbs) on a sliding cradle to strengthen the chassis 12" brakes and 16" light truck tyre/rims c/w break away brake system is also a compromise....the more you add to trailer the heavier it get and the more mods required ...sort off catch 22

[RobertB]

I have found it quite interesting that our Australian cousins are inclined to use truck tires for the trailers.

The published information on what tires to use says trailer tires (ST) have a stiffer sidewall to control sway.

Curious why the choice to use LT tires? What are the implications? No criticism, just curious.

Following is a list from a Carlisle (trailer tire manufacturer) publication:
"The construction, design, materials and testing used in ST Special Trailer tires meet the higher load requirements, duty cycles and
special demands of trailering.
– Polyester cords in an ST tire are bigger than in a comparable P or LT tire.
– Steel cords used in ST tires have a larger diameter and greater tensile strength to meet additional load requirements.
– ST tire rubber compounds contain chemicals to resist weather and ozone cracking, particularly conditions resulting from extended storage and the unusual duty cycles of trailer tires.
– The slightly shallower tread depth of a trailer tire reduces sway and rides cooler, which adds to tire longevity.
– ST tires feature stiffer sidewalls, especially in the lower section which:
– Reduces sidewall flexing causing the trailer to track straighter.
– Diminishes the risk of trailer sway.
– Lessens the risk of sidewall puncture and blowout.
– ST tires generally offer approximately 10% percent more load capacity than a similar LT tire and nearly 40% more than a P passenger tire."

[bartmac]

Very simple......trailer tyres as a seperate catagory don't exist in Australia as far as I'm aware....our market is soooo small compared to US....probably not much bigger than some of your states

[RobertB]

At least you have good beer (Fosters Bitter, green can) Makes up for alot.

[bartmac]

And you know.....we don't get Fosters in a green can.....probably made in the US for US taste.....actually we don't hardly get any Fosters branded beer.......BUT don't worry there's plenty of other beer

[Boblee]

VB in a green can, seem to remember that debate about trailer verse LT tyres a while back but can't remember the result but think the tyres I have on now are trailer tyres, damn checked the boat out yesterday and now might have to check it again.
Whatever they are they have lasted better than any others especially the originals.

[raycarlson]

you guys need to get with the 21st century and convert to torsion bar axles, you.ll never go back!!!! the ST LT tire thing has been beat to death on this board along with 5year lifespan and sidewall dressings, to each his own...........