Thursday, Jan 08, 2009 at 14:12
Heavy and Light vehicle braking systems are substantially different in design requirements.
The PRIMARY brakes in light vehicles are the front brakes due to large amounts of mass transfer forward under spike brake conditions.
Where the PRIMARY brakes on HV are the rear brakes due to less mass transfer due to longer wheelbase, load over the rear axles and the size and capacity of the rear brakes. (ie twin bogie and duals=4 times the traction of the front) but the trailer also plays a huge part in traction. When the truck brakes mass transfer would normally push down on the front and lift the rear but the trailer transfers its mass onto the
turntable decreasing the normal reaction and increases the weight on the rear axle.
The trials that were carried out for the implementation of ADR 38 (commercial trailer braking systems) found that timing did little to the attitude of the trailer under braking and while it is important...the braking capacity (effective retarding co-efficient) of the trailer was the most important factor.
If the trailers braking capaity is sufficient it will enable the combination to brake well...ie reduce truck front wheel lockup and nearly eliminate truck rear wheel lock up (jacknife).
My opinon of a dog type setup on a non-commercial vehicle would, in theory, control mass transfer and provide a setup that non-commercial vehicles are designed for. Having a front primary braking system, a dog trailer does not change the mass transfer on the towing vehicle. Where a pig trailer (typical caravan) does change the mass transfer of the tow vehicle and pushes down on the rear...hence the need for vehicle leveling and stabiliser systems for safe towing.
In practice and without seeing the report you mentioned...the logistics of engineering a dog type trailer setup for a non-commercial vehicle would be a PITA with large amounts of engineering and very hard to meet the ADR requirements.
Thats without the other types of problems mentioned like driveability and manouverability.
I agree with you, I think it all just gets into the 'too-hard' basket.
All the best
Matt.
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