Wednesday, Apr 11, 2012 at 12:17
"As far as I know, GVM is designed/tested/calibrated for on-highway driving only (no extreme stress due to corrugations) ...but I'm not sure if any manufacturer ever publishes a 'reduce by' or percentage (eg: reduce weight by 50%) figure for off-road conditions. "
Your comment reminded me of the email below that I received from Mitsubishi after asking a few questions about the towing capacity of the Triton. I would say that would apply to all vehicles, unless specifically stated by the manufacturer, and would include carrying capacity as
well.
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We acknowledge receipt and thank you for your recent enquiry regarding the Mitsubishi Triton.
Please be advised that Mitsubishi Motors Australia Ltd (MMAL) only release towing specifications for vehicles being used under normal conditions such as highway driving. We would not recommend towing this amount while driving on 4WD tracks or surfaces of this nature. The 3 Tonne towing capacity is a statement of the maximum permissible towing weight possible for this vehicle.
Thank you for your enquiry.
Kind Regards,
Simon
Mitsubishi Customer Assistance Centre
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Back in my National Service days, I drove an old WW2 6x6 Studebaker truck at a
driver training school. It was rated at only 2.5 tons carrying capacity despite having three axles, ten big wheels and a chassis like a tank. I initially thought it was an over cautious limit placed on it by the Army. I discovered years later on the net that it was the capacity specified by Studebaker. It was the maximum it could reliably carry in the worst conditions likely to be encounted.
This is just common sense. You can't expect a vehicle to carry and tow the same loads along a bush track as easily as it will do it on a highway.
The Army's solution to carrying a lot of gear with its Landrovers was to use a trailer instead of trying to beef them up. The little number 5 that has been in use since the mid 1960s weighs about 360 kg and will carry 500. That means it will carry close to the entire capacity of a Landcruiser and, when fully loaded, is only one quarter of its towing capacity. You would have to go out of your way to try and break a Cruiser in the bush with one of those hooked up behind and just mum dad and the kids and about 100 kg in the back. If you put the lot into and on top of the car and strengthened the sagging
suspension, that is when you can expect chassis cracks, broken wheel studs and cracked diff housings.
The other issue is the weight/mass problem that Collyn Rivers was stressing in those links I posted in thread 93028. Weight is static only. It is way above that as the car is bouncing along rough roads or is swinging at the ends of a long caravan. I think Collyn said it increases by the square of the rate of acceleration or something like that.
Whatever is behind the axle on those utes becomes a huge moving mass and slams down hard on the
suspension and diff housing when the wheels drop into a depression in the road. It then has to be caught by the housing and heaved back up again a split second later. The further it is from the axle, the worse it gets.
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