Tyre Tip 6 - Truck Tyre Noise

For some of us the sound of a powerful truck accelerating up through the gears or cruising past may be heaven on earth, but to others perhaps living adjacent to a freeway, it could be just plain objectionable noise that they have to cope with in their everyday life. Not only that, but if we turn the noise inwards (so to speak), high levels of cabin noise can be fatiguing to the occupants and thereby a safety issue.

 

All of these aspects have been recognised by the various authorities around the world, with a number of regulations being put in place or proposed for the future. Right now there is a schedule in Europe to specifically reduce vehicle and tyre pass-by noise levels significantly over the next few years, whilst locally consideration is being given to tightening current truck pass-by regulations.

 

Contrary to several opinions, tyres make a solid contribution to overall truck constant speed noise levels --- particularly drive axle traction types. A free rolling truck at 80km/h with engine switched off will come within a few decibels of a driven truck at the same speed. This is one reason why we are seeing the introduction of block design traction deep tread drive tyres in place of the old cross rib lug tyres. Yes, there is a small compromise in traction characteristics, but made up in lower noise levels and improved wear balance.

 

If we investigate the sources of tyre/highway noise, there are many contributors. The road surface itself can have what we call micro and macro roughness, or material utilised (think about a smooth concrete road and the noise it creates!). Conditions such as load, inflation pressure, speed, wear, weather, etc. contribute to the overall picture. And this is before we investigate the actual tyre input. Tread pattern, sizing, construction and compounding all add there little bit.

 

One of the "black" arts (pardon the pun) of tyre design is to develop a quiet running tread pattern yet at the same time provide adequate traction and performance. We can all recollect the old army jeep all service tyres that howl like a banshee, but are great in mud. So from the start the designer has to avoid the lateral lug configurations where possible. Obviously rib type tyres run a lot quieter than an aggressive lug pattern, but lose out in the traction stakes, hence the designer must compromise (we hear that a lot in tyre development) to achieve the desired outcome. Pitch sequences of the blocks or lugs are "hashed" up both longitudinally and laterally to ideally produce an even "white" noise of various frequencies, rather than the fixed single frequency of the jeep tyre. The designer may adopt up to five pitch variations in his chosen tread pattern.

 

It doesn't end there, with quite in-depth studies necessary to accommodate such aspects as groove resonance, air pumping, pattern vibrations, sidewall vibrations, road impact and snap-out effects, etc. Computer analysis can assist enormously these days in calculating all these obscure effects. In fact, designers can fairly well predict the performance characteristics of their creations before they leave the computer screen. Handling, braking, wear, noise, etc. can all be considered in their context prior to experimental build release.

 

I mentioned initially the contribution tyre noise has to driver fatigue. I believe here in Australia we may have a unique situation in terms of the widespread use of coarse bluemetal road surfaces which induce an inordinate amount of road roar up through the vehicle interior. This generated a large amount of development work in my days of passenger vehicles to suppress these noise paths through body structures, suspensions and tyres. This constant roar over our long transport distances must ultimately affect the occupants in terms of fatigue, and any tyre manufacturer that can assist in reducing this characteristic must be applauded.