DEAR
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SIR
TRRL AIRS ITS VIEWS
The article "TRRL: air hits roads harder" and your editorial comment "Suspending this belief, published in the 22-29 June edition of Commercial Motor, suggest that air suspensions can be more, not less, damaging to our roads than conventional systems. To draw this conclusion on the basis of one very small aspect among the wide range of testing we have done at TRRL is misleading, and the point needs putting into context.
First of all, there can be no doubt that, overall and by a wide margin, air suspensions are kinder to the road than conventional steel or rubbersprung suspensions. This is clear in our results presented at the recent International Symposium on Heavy Vehicle Weights and Dimensions.
At all speeds and on all types of road roughness, airsuspended trailer bogies produce lower dynamic loads than steel or rubber suspensions. Recent tests on single-drive tractive units follow the same trend. Both roadside surveys and full-scale laboratory tests have shown that air-sprung multi-axle semi-trailer bogies equalise much better than the majority of steel sprung bogies.
Your article referred to the One exception: in all this testing, which was when the vehicles were run over a one-inch plank to simulate a sudden discontinuity in the road surface.
The peak transient dynamic loads across the plank were higher for air-sprung axles than steel-sprung axles, except at speeds over 70-80Iun/h.
This type of surface irregularity might represent some potholes or, for example, mis aligned bridge expansion joints, but it is an infrequent occurrence on the road, and extensive roadtests have shown that, overall, the poorest air suspensions cause less road wear than the best conventional steel.
It will, hopefully, be possible to improve steel suspensions considerably. There is also no reason to expect the observed response of air suspensions to the plank to be an unavoidable aspect of air, and improvement will doubtless be possible in air suspensions too. TRRL's current programme of testing a range of existing suspensions should point the way to how these improvements might be achieved.
L Gyenes, Transport and Road Research Laboratory, Crowthorne, Berkshire.
We disagree that one-inch irregularities are rare. Ruts, bumps and potholes are a blight on our under-maintained roads — and as air suspension is a potential Pre-condition of the belated tonne limit, anything that relates to its superiority over steel is, to say the least,
noteworthy. Ed. GRASS ROOTS GROUSE
• In your issue 15-21 June, your editorial refers to "The haulage industry being knocked hard again".
Amazingly you also referred to the lone battle of the FTA (Forty Ton Association). As far as is known in our local subdistrict of the RHA, the official RHA line is strictly neutral in spite of members being fiercely against it, regardless of fatuous remarks made by our national chairman at the RHA Dinner recently. He is as out of touch with grass roots as you are!
When the GVW went to 38 tonnes who got the benefit? Certainly not the haulage industry as it immediately depressed rates — especially at the lower end of Special Types and in the tipper industry.
On your second point about the militancy of the French, as soon as this sort of thing is mentioned in RHA circles the permanent staff start fidgeting, go white and start packing their briefcases.
Personally, I can think of only one thing in the past 20 years which has worked to the benefit of the industry and that was the drivers' strike in the seventies. Then we could get the rates up!
A H Tonge
Freight Forwarding, Stoekingford, Nuneaton.