How is Towing Capacity Calculated?

[Lionelgee]

Hello All,

Just wondering how towing capacity is determined?

For example,

Holden XY Commodore is has a braked towing capacity of 2,100 kg
XJ Jeep Cherokee Sport Towing Braked 2,265 kg
1995 Land Rover Discovery TDi Auto 4x4 Towing Braked of 4,000 kg

All the braked towing capacities were quoted from different vehicles that were advertised on Carsales.com.au.

I thought the Discovery's were 3500 kg?

What surprised me was the Jeep Cherokee's braked towing capacity was not that much more than a Commodore!

Does the main part of the calculation of Braked Towing Capacity involve the Tare Weight of the vehicle?

Kind Regards
Lionel

[pop058]

Hello All,

Just wondering how towing capacity is determined?

For example,

Holden XY Commodore is has a braked towing capacity of 2,100 kg
XJ Jeep Cherokee Sport Towing Braked 2,265 kg
1995 Land Rover Discovery TDi Auto 4x4 Towing Braked of 4,000 kg

All the braked towing capacities were quoted from different vehicles that were advertised on Carsales.com.au.

I thought the Discovery's were 3500 kg?

What surprised me was the Jeep Cherokee's braked towing capacity was not that much more than a Commodore!

Does the main part of the calculation of Braked Towing Capacity involve the Tare Weight of the vehicle?

Kind Regards
Lionel

All specified by the manufacturer IIRC. I would have thought the "XY" (VY ?) commy would have a special HD towbar for it to be 2100.

One of my Discos has a 4T towbar on it but the limitation is the actual towball itself. A 50mm ball is rated at 3500 max.

[Lionelgee]

All specified by the manufacturer IIRC.

Hello Paul,

Thanks for the reply Paul. Yes - however how does the manufacturer calculate the recommended braked towing capacity? There must be some form of formula?

For example, supposedly when a local light aircraft manufacturer's product was being inspected the aviation people asked what formula they used to calculate the load the wings could take and what was their answer? The people said, "well we weighed sandbags. We put them on the wing one at a time and counted them until it went 'snap'. That was how we got our answer"! Apparently, the inspector was not happy that they could not quote a formula.

Kind Regards
Lionel

[Blknight.aus]

from very vague very old infrequently used memory and recolection.

an unbraked trailer was allowed to weigh up to .5x the Vehicle Tare
an over ride braked trailer was allowed to weigh up to the vehicle gvm
a command braked trailer was allowed up to 2xGVM

but that only covered the tow assembly as far as the manufacturers limits were concerned, other things like the size of the ball or hitch or govt regs imposed other limits. such as the limits for the trailers (750kg unbraked, 2000kg override and I think currently its at 3500kg or 1.5xveh GVM whichever is less for command brakes in a light vehicle application)

[Homestar]

All specified by the manufacturer IIRC. I would have thought the "XY" (VY ?) commy would have a special HD towbar for it to be 2100.

One of my Discos has a 4T towbar on it but the limitation is the actual towball itself. A 50mm ball is rated at 3500 max.

You can get a higher rated 50mm towball - it has a much wider thread and they wouldn't fit a normal tongue without the hole being drilled larger. My FIL used to have a boat that weighed right on 4000kg with the trailer and towed it with the RRC (The RRC has a 4000KG towing capacity) - with a 4500KG rated ball - similar to this one - https://www.couplemate.com.au/trailer-parts-shop/towballs/50mm-x-4500kg-tow-ball-1-14-thread/.

It says on that site that you need approval to use it, but this arrangement was supplied by the trailer manufacturer to the FIL and he never got pinged for it, but that was some time ago.

Guess how fast a 3.5 RRC goes with 4 tonnes on the back of it.... :D

[Mick_Marsh]

from very vague very old infrequently used memory and recolection.

an unbraked trailer was allowed to weigh up to .5x the Vehicle Tare
an over ride braked trailer was allowed to weigh up to the vehicle gvm
a command braked trailer was allowed up to 2xGVM

but that only covered the tow assembly as far as the manufacturers limits were concerned, other things like the size of the ball or hitch or govt regs imposed other limits. such as the limits for the trailers (750kg unbraked, 2000kg override and I think currently its at 3500kg or 1.5xveh GVM whichever is less for command brakes in a light vehicle application)
Interesting. So my Perentie could possibly tow 11.2t. I might have a good chance to get it re-rated to 4t.

Have you got any ideas where I could find any further info on this?

[JDNSW]

The towing capacity of a vehicle is specified by the manufacturer, although there is no obligation for the authorities to respect this. (Although I think that today in Australia they usually do today)

Effectively, the manufacturer is saying that the drive train, suspension and structure is capable of towing this mass, and by placarding it at this we accept that we can't void the warranty if you tow this mass. (subject to limitations such as braking, weight on towbar, tow pack etc)

There is no specific formula for calculating it, and the figure specified for any vehicle will be the result of the manufacturer's experience and the market they are aiming for. And says nothing about performance while towing either.

John

[Blknight.aus]

Interesting. So my Perentie could possibly tow 11.2t. I might have a good chance to get it re-rated to 4t.

Have you got any ideas where I could find any further info on this?

a fully loaded 6x6 will tow a lot more than that under the right circumstances.. I can guarantee that it will tow at least 11.54T worth of tracked vehicle, I just wouldnt advise doing it in any taller gear than about 2 low

key word was those are the very old guidelines for what you could get a tow assembly rated to, not whats in place now.

Fozzy can tow 13T.. doesnt mean Im allowed to by law.

Australia (AFIAK) is currently limiting at 3500KG for light vehicles and (guessing here) the Vehicle GVM for mediums with a command braked trailer.

[DiscoMick]

I notice the manual for my 110 says 3500kg braked but allows 4000kg under some circumstances (don't have the manual handy and can't remember the details).
Personally, I wouldn't be happy towing anywhere near that - just too much, I reckon.
The other day I saw a Colorado towing an enormous and long dual-axle caravan down the Bruce Highway. The front of the Colorado was lifted up a lot, the back was right down and the guy was going quite slowly. I don't know if it was legal, but it sure didn't look safe.

[cripesamighty]

I remember saving this page from a RRC manual that was put up by somebody on this forum. In emergencies, max towing weight in low range and going slow was 6t. It might not necessarily be legal or comfortable to do so though......

106404

[Tins]

I can't point to a formula, but I know that load mass ( note that; mass, not weight ) is very carefully calculated, and a vehicles capacity to tow is an engineering calculation and not a guesstimate.
In this country it is difficult to understand how the authorities interpret the manufacturer's stated limits, but it's important to note that these limits are arrived at through engineering, and the licensing authorities will not accept a manufacturer's stated limit simply on their say so.
A normal car, LR's included, have two stated figures: Maximum total mass of trailer, and max total down on tow ball. This is then modified by the braking component, as Dave said.
The maximum mass will depend on many things. The mass of the towing vehicle, the type of construction of the towing vehicle, the manufacture and placement of the towbar, the type of tongue or hitch, the type of towball, the list goes on. Pintle hooks can tow more mass than a 50mm machined ball ( the old two piece towballs are now illegal ). The square type receivers ( known as Haymann Reese type here, but I doubt they invented it ) can tow more than the old two bolt type tongue we all swore at when we knocked our shins on them.
LR were one of the first manufacturers to include a serious towing package, and we should thank them for it.

Anything with a ladder frame chassis will tow more than a monocoque.

Now, why does a Ford Ranger have a higher capacity than a HiLux? Because Ford has the papers to prove it. Is a Ranger stronger/better braked/ more powerful?? Who knows. But I doubt it. Is a D2 a better tow vehicle than either of them? Almost certainly yes. For now.