I stopped on the A50 dual carriageway nr Derby at 5am today for 5 minutes breather.
It was typical traffic of that time of day, car van or truck about every 5 to 20 seconds both directions.
I had a bit of a surprise when i realised that some cars going by were making appreciably more noise than most trucks, mainly tyre roar, but the unmistakable harsh sounds of CR diesels under load added to the cars' clatter too, and a thoroughly unpleasant sound it is too.
In comparison most trucks going by sounded 'softer', the tyres making a gentle rumble as against the raucous jarring sound many low profile car tyres make at high speed.
Obviously there is a speed difference, the trucks would be travelling 50 to 55 mph and the cars anything up to 90ish i suppose.
But considering most of the trucks were running the equivalent of 20 tyres (most trailers are now super single's, double width tubeless trailer tyres), i was quite surprised.
The road surface at that section is good smooth tarmac, would have maybe been a different story nearer Stoke on the concrete.
Why are car tyres so noisy?
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Doubtlessly the tread patterns on truck tyres have moved on from the simple zig-zag patterns of old, however, I would still expect a truck tyre to have a more continuous rolling contact rather than individual tread blocks heavily slapping the road.
Eact tread block impact effectively plays on the drum skin of the tyre, and, owing to the geometry of the tyre and road, the resulting bending waves in the tyre couple extremely well to the air.
When there are multiple sources, typically, the ear will pick out the dominant one - especially if it has an identifiable tone.
Another way to consider this is to look at the slightly odd way that sounds in dB are added. If you have 2 uncorrelated sources, one at a sound pressure level of 72dB, and one at 75dB, the total SPL is 76.8dB. So, despite a truck having 20 wheels, you wouldn't expect a high SPL just because of that.
I remember attending a sparkling seminar given by the late Manfred Heckl (co-authour of one of the seminal books on the subject - Structure Borne Sound), where he confessed that he had found the problem of tyre noise by far the most complicated subject he had ever tackled.
Having said all of that, I would expect that the vehicle's speed is ranked high among the dominant factors.
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I am glad that you have cleared this up for us, Mr Cruncher.
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It may well be true 'close-up' as you were - but I doubt that higher range of sounds carried as far the the lower rumbling of the truck tyres/wind noise - I live about 1.5 miles from a major trunk road, and trucks are the predominant noise makers - the thinner sounds of cars just seem to whither away before they reach my house. Compare & contrast with whale song & dolphin chatter - the former can travel hundreds, if not thousands, of miles.
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Perhaps lorry tyres have, on average, more tread?
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Well chaps, as usual NC provides an explanation that makes perfect sense, thanks for that.
I know a little about the reason for tyre roar now.
I wonder if the low aspect ratio of many car tyres exacerbates the noise problem, tyres with no sidewall flexing must hit the road harder?
The first time i ever drove a car on low profiles was my friends XR3, i took his family to the airport and picked them up again 2 weeks later, only an hour each way, but very tiring (no pun) with the severe tyre roar that could be felt as well as heard.
Jolly glad to get out of the thing.
Modern truck tyres are designed with specific axles in mind, and its only drive axle tyres normally that have any sort of block effect in the treads.
As NC says correctly most of the truck tyre's tread stays in permanent contact with the road, i never thought about that slapping action as a cars block tread hit the road, explains why off road tyres make such a racket when used on the road.
It may be true that the trucks noise carries further, but it appeared much softer by comparison at close proximity.
In fact WB thinking about it we live about 2 miles from a dual carriageway and its much quieter at the weekend, which compounds your observation, however the weekend bikers are a different problem altogether.
It must be hellish living near concrete road sections, its deafening enough just grabbing a bacon sarnie from a roadside van.
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