Thursday, May 10, 2012 at 11:53
sorry GT.....still an over simplifcation and a biasing of the argument toward one particular engineering consideration.
You simply can not say this or that factor has nothing to do with another.
In the not too distant past there was one single peramiter that determined towing capacity of pasenger cars in most states and that was vehicle mass, you could not tow more than the towing vehicle weighed.
Things have changed.
We live at a time when many of the manufacturers are pushing the limits of the vehicle formats. It is very reasonable to see that as they push the envleope any the various engineering factors can become a limitation.
It is a fact that IF a manufacturer wishes to nominate a specific maximum towing capacity, that vehicle MUST be capable of supporting a certain persentage of that capacity as drawbar down force.
IF the vehicle cant support that persentage of down force they can not mominate the higher towing capacity.
Look at the latest crop of 4 cylinder utes, the manufacturers are nominating towing capaicities nealy twice that of the precceding generation, on a format that remains largly unchnaged on vehicles that do not weigh too much more.
Also note that after 30 years of sticking with the same nominated tyre size more or less across the brands, it has become necessary to increase the tyre size on 4 cylinder utes to permit the increased rear axle loads.
Be asured that these very high permissable towing capacities are pushing the envelope in every peramiter.
On one vehicle it may be cooling, on another it may be the strength of the gearbox ( typical of US manufacturers) on another it may be rear axle strength or chasis strenght ( as we are seeing from the reports) or even vehicle stability.
It is simply unrealistic and nonsensical to say that all manufacturers base their towing limits on one single peramiter.
AND experience shows that to be the case, testified to by the types of "in use failures" that we are seeing when people push the bleeding edge of the towing capacities.
Further manufacturers such as Toyota standardise engines and transmissions across a very wide range of vehicles...a very wide range of vehicles that have significantly differing towing capacities.
The biggest example is the hilux V the hiace, two vehicles with very similar uses, load carrying capacities and GVM and in the 2wd base model very similar if not identical engines and trasmissions.
BUT over the decades and several incarnations, the van has always had arround half the towing capacity of the utility.
There is definitely something other than engine capacity, transmission and cooling being considered here.
cheers
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