Car carrier operators take note

While wandering round the car carrier, I spotted the uneven wear on the tyre pictured here. I sent the pic to Marcus Haw, technical boffin at Bridgestone who works with us on our Brake & Tyre Watch projects, for his expert comment. His response should be heeded all car carrier operators. Here it is:

"The tyre has three main concerns, all of which are pretty common with car carriers. I hate those things. You have more irregular tyre wear problems on one car carrier than in an entire fleet of flatbeds.

"The three concerns are the obvious severely dropped shoulders, some undulation wear starting on the centre ribs, and feathering on the lateral sipes. If you look closely, the ribs are also showing a rounding of the edge closest to the camera and sharpening of the edges furthest away. This is lateral scrub and goes hand in hand with the feathering, showing that the axle is pointing slightly to the right.

"The other wear patterns are the indications of the characteristics of carriers. Their loads are more dynamic than liquid and tyres go through hell on these things. First you have the height which causes severe side to side 'rocking'. While this rocking is taking place, the loaded cars' suspensions are also working, adding to the already severe load transfer constantly happening from one side to the other. Remember that these cars are only secured at their wheels and they have full movement of their suspensions all the time. For the same reason, there is also exaggerated "porpoiseing" occurring all the time, the rocking ensuring that the tyres shoulders are stressed beyond their designed levels, and the fore/aft movement making sure that load is constantly transient between an over, and under situation on the tyres. Hence the undulating rib wear. These are also inherently unstable vehicles and a lot of "dancing" of the trailers takes place while travelling affecting the trailer tyres and the truck tractor tyres. This also works from shoulder to shoulder on the tyres.

"So, between the rocking and the dancing - and the fact that the tyre's belt edges are in the shoulders - tyre failure is very high with these vehicles. All these factors are compounded because most of the car carrying companies run their tyres at minimum safe inflation pressures to soften the ride. This allows the tyres even more flexibility, accelerating the wear already happening. Tyres with very broad shoulder ribs are better in these operations but still suffer."