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PostPosted: Dec 23rd, '17, 15:33 
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Like several others, I'm considering my next car. I've asked the same question that's been asked a thousand times already on this and other caravan forums - what cars can tow my boat (or caravan)? I've entered the murky world of tow capacities and various laudable attempts write spreadsheets to do the sums. Even with the best spreadsheets, the results are usually inconclusive because you need a swag of weights and measures, and manufacturers are reluctant to release them. I suppose you can physically look in the owners' manuals, but its tedious. It seems to me that the car industry is following the telecom industry's lead by obfuscating essential information to the point that a rational like-for-like comparison is impossible, and buyers give up and resort to instinct (which has already been cleverly manipulated by the brand).

Anyhow, the best information I can find on-line is a 2013 RACQ guide downloaded from here, and attached.
http://www.centaurproducts.com.au/fileadmin/user_upload/files/Nov_2013_Towing_Guide_Complete.pdf

If you have a more comprehensive, or reliable guide, please post it here.


Attachments:
File comment: Nov 2013 RACQ Vehicle Towing Mass Guide
Nov_2013_Towing_Guide_Complete.pdf [1.89 MiB]
Downloaded 49 times

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PostPosted: Dec 23rd, '17, 18:16 
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Redbook will give you dimensions, weights, etc for each individual model and trim level. For example, my ute has a kerb mass of 1692kg. Mind you obviously they have no idea what you've added to the bare car; I was about 2450kg plus driver last time I went over a weighbridge. I was startled!

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PostPosted: Dec 23rd, '17, 19:11 
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zebedee wrote:
Redbook will give you dimensions, weights, etc for each individual model and trim level. For example, my ute has a kerb mass of 1692kg. Mind you obviously they have no idea what you've added to the bare car; I was about 2450kg plus driver last time I went over a weighbridge. I was startled!


Considering that includes accomodation, a power station, workshop, and most likely seval hundred doohickeys, that's surprisingly light.

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PostPosted: Dec 23rd, '17, 19:12 
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I sense your pain. In the research I am doing, pertinent facts are withheld by manufacturers. Claims of 3500kg ATM and 350 on the ball really are marketing numbers - there are so many gotchas. For some manufacturers the math does not add up. Case in point is the BT50. The Gross combined mass seems to be 350 kg too low . . . the GVM + GTM or GVM + ATM less ball loading is 350kg over the claimed GCM . . . I suspect a snafu somewhere . . impact is that no, you cannot tow at maximum ATM and ball weight with the BT50.

It is relatively simple to figure out the payload capacity (fuel, luggage, people etc) left in the vehicle after a trailer is connected. What is harder is the axle loading. How is this weight distributed across the axles. Some manufacturers provide maximum axle loading but this is only helpful if you go to a weigh bridge. What would be nice is this maximum axle loading and the TARE axle loading to be defined. Then the increase from TARE can be judged for the rear axle as the ball weight and other payload hits.
Close enough is to take the prospective car to a weigh bridge with a full tank of fuel (or near empty as this will be the TARE weight) and get the axle weights front and back and compare to the manufacturer maximums THEN some math can be done for example the ball weight will hit the rear axle almost exclusively, weight in the trunk will do the same, then passengers evenly apportioned front and rear and luggage the rear again . . . you can now make some quantitive math.

I do believe that many manufacturers will have a greater allowance from TARE on the rear axle than the front but as these axle TARE numbers do not seem to be published it is guess work . . . or go to a weigh bridge as above.

I would like to believe that the available payload after a trailer with maximum ATM is connected is safe. That this payload can be assumed to hit the rear axles and that the maximum rear axles load factors this in . . . so as long as you keep within the GVM and GCM then all good an roses and the axle loading should be fine . . . but as in the case of the BT50 I have seen enough inconsistency in some numbers to very very suspicious of such an assumption.

But one easy decision - do NOT buy any car with a sunroof . . . you do not need the 100+kg reduction in payload that this causes. Do not buy a car will bull bars as well . . . extra weight again that detracts from payload possible after trailer connected . . . . .

I have attached an xls I am working on . . . simple tabular format this time . . no fancy stuff ;-)
Tell me what cars you are interested in and I will add them . . or you can . . .

Attachment:
Towing limits of a vehicle v05.xls [52.5 KiB]
Downloaded 31 times


Edit: some typos

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PostPosted: Dec 23rd, '17, 23:12 
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Jim, your comments re tow ratings being marketing driven, I agree.

I did a lot of work with heavy vehicles where vehicle ratings were done with the types of loads and routes considered.

The biggest factor in most heavy vehicles is the need to dissipate heat from the engine and mechanicals.

The next criteria is the forces and moments applied within and on the vehicle.

Its a good time for an example to highlight the differences.

The first prime mover is a heavy haulage truck rated to tow with a GCM of 150 tonne. It will have 450 kw of engine with between 20 and 60 gear ratios. Its axles will have hub reductions on each wheel with independent lubrication and oil coolers on the hubs, differentials and gearboxes. While the vehicle will pull 150 tonnes, its unlikely to do this for more than a single shift and the average speed is relatively low because the axle loads limit speeds on bridges and other features of the route. Ambient temperatures will be below 35 degrees C because most first class roads will be damaged by this type of axle load, hence they don't work in extreme conditions at high speeds. Limiting factors are things like hauling up and down hills where hubs overheat and driveshafts break. Even though they have 450 kw, cooling the engine is seldom a limiter on the truck operation.

Second look at a road train rated to tow with a GCM of 150 tonnes. It will have a 450 kw engine with the biggest cooling system possible (that is why bonneted trucks work better because they have bigger radiators and bigger clearances where the air flows after the radiator). The gearing will be about 30 ratios with 15 in the gearbox and a two speed differential. These trucks try to travel at high speeds and typically run 2 or three shifts most days. They travel in hot weather exceeding 40 degrees C. Towing multiple trailers means wind resistance is a significant part of the load, cattle trucks have more drag than others due to turbulence. Crosswinds increase drag dramatically due to the increased apparent head winds. So a road train in hot weather with a crosswind has significant and continuous heat loads on everything including the engine, gearbox, cabin, differentials and tyres. During hot conditions, its normal for the drivers to change down gears to spin the fan faster and slow down to reduce the load until the hot mechanicals are stable at the slower speeds.

So you have two heavy duty trucks rated to tow 150 tonne yet they are very different due to the loads and duty cycles they are rated for. Either truck would not last a few days in the other truck's applications, the road train would quickly break axles, clutches and driveshafts and the load loader truck would overheat its hubs and differentials.

Now we have light vehicles sold with 3500 kg tow ratings and I'm skeptical that these vehicles can cope with the worst 3500 kg trailer at highway speeds for long distances in an Australian summer.

About the ugliest 3500 kg trailer I can imagine would be a Nolex 30, its ugly due to its weight but also its frontal area and turbulence with rigging etc. it makes high drag which will use all the power the tow vehicle can muster. Put it in a crosswind at 100 km/hr and I suspect there are few vehicles that have been discussed here would be reliable (actually I'd bet they all would expire if driven with a Nolex 30 at the speed limit from Melbourne to Airle Beach).

So what would I use to tow a Nolex 30 across Australia? A 3 tonne or 4 tonne truck.

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PostPosted: Dec 24th, '17, 03:01 
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I once towed a 25,000 litre plastic water tank on a car trailer from Belgrave (SE outskirts of Melbourne) to just past Wangaratta (~270km up the Hume) with my V6 auto Rodeo.

It was road legal at 2.5m wide and 4.2m high.

I could just about get it out to 100kph but 80kph in 3rd (of 4) was much easier and my fuel consumption was still ghastly. The trailer was rather intimidating to tow, yet it was shorter, no wider, and half the weight of the Castle! I have no doubt that towing that load on that route on a regular basis in hot weather would wear out a Rodeo rather quickly. Weight alone is not the whole story.

The Rodeo nominally weighed about 1700kg, had a GVM of about 2700kg, a tow capacity of 1800kg and a GCM of about 3700kg (GVM +1000kg). Nobody was pretending it could tow 1800kg while itself fully loaded; to tow 1800kg it needed to be lightly loaded.

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PostPosted: Dec 24th, '17, 09:07 
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INMA and Zeb, with respect, my primary concern is not whether I will break my car by towing my current or future boat. My primary concern is whether I am road-legal and insured.

OK, so I'd be unwise to tow something big for long distances with an undersized car or truck, and I appreciate your advice, but I won't be fined and uninsured.

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PostPosted: Dec 24th, '17, 09:12 
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bachus wrote:
I sense your pain. ...


Bachus, yours is one of the laudable spreadsheets I referred to earlier. And, it seems, you're right about the 'gotchas'. I think it iniquitous that the manufacturers can claim a 'tow capacity' that can only be attained if no-one (not even the driver) can sit in the car.

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PostPosted: Dec 24th, '17, 09:23 
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Bachus/Jim - just checked out version 5 of your spreadsheet, and it looks convincing. Thank you for spending the time to attempt to make sense of the math.

My broad requirements are to tow my Austral 20, which is about 1600kg, plus stuff. And needs to survive the journey (INMA and Zeb - I am listening to you, too). Auto Diesel is probably the way to go

Possible cars;
Toyota Landcruiser Prado
Mistubishi Pajero
Ford Territory
Isuzu MU-X

... all of which are advertised at 2500 to 3000 kg, but might consider lighter vehicles, because car will only be used for towing on occasion ...
Kia Sorrento
Hyundai Santa Fe
etc.

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PostPosted: Dec 24th, '17, 10:31 
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Have a look at the 2010 onwards Outlander . . . . 2013 will still be under factory warranty . . . the numbers stack up pretty well alongside the Challenger at least.

I will add the list above - see what eventuates.

One thought I am tinkering with is that some manufacturers only specify TARE or KERB (TARE plus full tank fuel), PAYLOAD and do not detail much else. The thought I have is that the rear axle must be rated to allow 100% of the payload to be applied to the rear axle. This might provide another analysis angle.

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PostPosted: Dec 24th, '17, 11:13 
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Found this in my travels:

https://docs.google.com/spreadsheets/d/ ... edit#gid=0

Found in this forum: http://www.pradopoint.com.au/showthread ... d-database

edit: of more use in hard to find numbers . . e.g. did not spot that the BT50 numbers are not consistent

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PostPosted: Dec 24th, '17, 12:57 
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For anyone towing heavier loads with a modern car, I'd suggest buying one of these or similar and using it to see what your engine management system is doing.

http://www.ebay.com.au/itm/ELM327-OBD-I ... SwlMFZGqUg

Logging the data on a premade sheet by hand or if someone here can set up an Excel spreadsheet to log the data might help when the towing gets tough.

Most of us are smart enough to figure out legal loads, the next bit of information that will come in handy is the various temperatures you can read from the scan tool.

If you want to make heavy towing simpler, this would be just as effective as anything else I can figure out.

Sorry if this is off topic but if you are planning to get near these vehicle's GCMs, wieght is just a legal issue.

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PostPosted: Dec 24th, '17, 13:01 
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New version attached. I have added the vehicles mentioned above.

Changes made:
Added manufacturers payload - calculated payload cannot exceed mnaufacturers payload less ball weight
** Single entry point for ATM and BALL percentage of ATM
Changed yes / not to TRUE/FALSE so that logic expressions can be used
Added test, if cannot tow then make the payload possible zero
Reduced payload - split into front and rear axle, assumed 90kg per front seat passenger on front axle, the rest for rear axle payload

I will look at making this a google drive spreadsheet . . . anyone can then edit / add to it.

Attachment:
Towing limits of a vehicle v06.xls [72 KiB]
Downloaded 31 times

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PostPosted: Dec 24th, '17, 17:44 
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Google drive version here: https://docs.google.com/spreadsheets/d/ ... sp=sharing

I hope this works - first time I have tried this. The conversion from XLS to this was pretty seamless - a few issues but largely easily done.

It contains a working sheet and a backup copy if you muck it up ;-)

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PostPosted: Dec 24th, '17, 23:13 
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Bachus, thanks again.

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PostPosted: Jan 1st, '18, 14:36 
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More updates here:

https://docs.google.com/spreadsheets/d/ ... sp=sharing

I have added the new Ford Everest. Luke if you catch this look at the Sahara's . . . with 80ltr fuel and two front seat passengers - not a lot left in payload if you tow 3500kg.

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PostPosted: Apr 22nd, '18, 21:54 
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Someone played silly with the online xls - I have restored the working copy - re added the Ford Everest.

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