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Here’s what catastrophic rim failure does to a tyre – a rim collapse, as a primary cause, can be proved. Don’t blame the tyre and look further to prevent more such failures.

Price versus quality is an issue we have raised in FleetWatch on numerous occasions warning that making a purchase decision on the basis of an up-front ‘cheap’ price will cost you in the long term. In this article, Dave Scott, FleetWatch’s technical correspondent, brings to the table proof that these warnings are not unfounded. In this case, it’s shoddy wheel rims. What’s next?

Silent operating budget theft is occurring through container loads of rim-junk being dumped on our market. Cheap-’n-nasty, low quality truck rims are being sold to unsuspecting operators. How does one get to notice these ‘vrot’ safety critical components? Thanks to Bridgestone tyres taking an on-going look into abnormal tyre wear, I was called on to examine a new rim that looked as if it had been hand-made to approximate tolerances. The process of eliminating all probable causes for excessive tyre wear took Marcus Haw, Manager Field Engineering at Bridgestone South Africa, into examining rims and what he found was both pathetic and scary.
 

This is a prime example for ‘Rim Robber’ products. It’s paint that hides many evils but cannot conceal shocking dimensional quality shortfalls.

Failure analysis expert, Patrick Swan also examined a rim. Cursory inspection revealed flawed welding – combine this weakness with inaccurate machining and the forecast in Swan’s terms is "Early catastrophic failure." And if a rim is visually and dimensionally so bad, it’s safe to assume that no care has been taken with basic steel quality where lab rawmaterial tests on similar examples have revealed life-shortening factors -

• High level of inclusions: sulphides and alumina

• High concentration and alignment of sulphides in the disc

• Stringers – lines of sulphides – in the steel that is typical of recycled materials

• Regions with heterogeneous granulation near the borders.

Says Swan, "All of this means that the fatigue life is greatly reduced to enhance early failure."

The knock-on effect of a rim that is out of round, badly machined, welded with weak stress points and variation in dimensional tolerances is massive. ‘Rim Robbers’ – yes, that’s a good description, are ‘junking’ our road transport industry with sub-grade wheel rims. Why ‘Rim Robbers’? What they are robbing is tyre life, shockabsorber efficiency, road surface life, driving comfort and road safety – just to name a few operating cost impacts. Any part of a truck subjected to constant vibration will suffer premature failure right down to hub seals and foundation brake components. An out-of-round wheel that does not even run straight is like building in a permanently bad road surface regardless of where a truck operates.

Was it in the rim manufacturer’s mind to produce a rim for all reasons and seasons – a sort of one type fits all? The stud holes are an amazing mixture of holes, some with countersinking for washers and some without. There’s no way anyone will be able to fasten this mess – the wheel will probably come off well before the rim fails!

In spite of paint, shoddy welding is visually apparent.

Haw points out that a rim with so many dimensional and material faults results in total tyre failure. The problem with a disintegrating tyre is destruction of the rim in the process and the natural perception is that it’s all the fault of the tyre. Not so. The good news according to Swan is that "Forensic investigation will prove what happened either way – what caused the failure." Other expert opinion notes that tyres will always fail long before the wheel because they will never stand the increased stress over the distance – tests of faulty rims show that they destroy three to four tyres per wheel test!

Here are some further characteristics of low quality rims -

• Out-of-spec disc flatness values to cause loosing of stud nuts and broken studs that will initiate cracks on the disc flange

• Poor finishing quality – manual grinding operations are clearly visible

• Poor assembly welding quality – too much undercut on the rim section and the welding shape is much too concave

If the company buyer is strutting for approval on achieved rim purchase prices, then think again. It’s time to measure what you’re getting. Rims must be traceable, dimensionally standard with details on the steel specifications and safety compliance. There are international wheel stamping norms – either SAEJ179 (Society of American Engineers), ISO -3911 (International Standard Organisation), or EUWA ES.08 (European Wheels Association) apply and are acceptable. Every one of these standards has obligatory information that provides dimension, manufacturer logo, date and part number plus additional info according to the standard.

As usual we are watching the doughnut and not the hole. The doughnut is the tyre for which we readily blame poor performance instead of taking a long view of all probable causes. The hole is the rim – and it’s a big black hole that is swallowing profits. All wheelassociated component costs run in escalation with the impact of a poorly manufactured rim.

I have walked through fleets that seem to have mysteriously acquired rims from different sources. The colours and rim condition alone tell me this. Tyre theft abounds and rims go together with this issue – no one will take your tyres and be kind enough to leave your rims. It’s time to take stock of rolling wheels – watch this space as we are looking to expose more examples of this unacceptable junk and the retail source into our market.
 

A road safety crusader – Bridgestone’s Marcus Haw – takes an integrated view of wheels on the road. While his primary interest is tyres, he is not jumping to conclusions and investigates the complete wheel in its operating environment.