The test of a good towbar
The failure of a towbar can have catastrophic consequences on the road, should a trailer break free and plough into other vehicles or even pedestrians, yet most people rarely give it a thought when purchasing one for their car, SUV or ute.
With the availability of low-cost towbars that are often not built to New Zealand standards, or even second-hand towbars taken from another vehicle, the chances of such a failure have been increasing in recent years.
New Zealand’s leading towbar manufacturer, Auckland-based
Best Bars, has documented evidence of poor towbars being sold in New Zealand to unsuspecting vehicle owners.
“It is worrying, as we have complained for years about the NZ Standard that was supposed to have been adopted into legislation for towbar design, manufacture and fitment, but there has been no movement from lawmakers to protect the public by making this mandatory” says John Frear of Best Bars.
Research carried out by Best Bars some years ago showed evidence of at least a couple of thousand substandard towbars being fitted to New Zealand vehicles each year and Mr Frear says the situation has not changed.
“That’s many thousands more vehicles that are using our roads with potentially dangerous towbars, since we carried out that research.”
Common problems associated with poor towbars range from the use of thinner metals, inadequate fastenings, incorrect fitting and poor design. So what does make a good towbar? John says it starts on the drawing board, or in the case of towbars made by Best Bars, on the computer screen, with information drawn from three key sources: on-vehicle analysis & measurement; scanned 3D images of vehicles; and vehicle CAD data.
Once the vehicle has been rated by the manufacturer for towing and relevant data collected, design concepts for the towbar are then validated via Finite Element Analysis (FEA), a software tool that quickly and accurately evaluates the stresses and strains the towbar will be placed under when in actual use to determine if the design will pass the regulatory tests.
This doesn’t happen overnight. Best Bars has a large team of experienced engineers, project managers and technicians who develop and review every towbar design at each stage of the process.
Once a concept design is approved, an engineering prototype is manufactured and the towbar is then put to work on Best Bars’ testing facilities, where it undergoes a static and/or dynamic test.
The static test is generally performed with the towbar mounted on the vehicle, with force being applied through the tow ball in various directions to determine the strength, performance and interaction with the vehicle under different loads.
The dynamic test is often performed with the towbar mounted on a specially designed rig, and then subjected to continuous loading/unloading of forces for up to 2-million cycles. It duplicates the tremendous forces exerted on a towbar, not just in a normal vehicle life cycle, but for far longer than most people will ever use it.
All towbars must pass the prescribed NZ Standard (NZS5467), or the legislated Australian Standard (AS4177 and ADR62), along with any motor company specific tests that have been requested over and above this. Once a towbar design has been validated, tested and complied, then manufacture can begin.
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