Cutting Down the Spray
Page 47
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THE spray generated by many corn mcrcial vehicles can be reduced considerably, NA it hout resorting.to a reduction in speed, f-s fitting mudguards arid flaps on the lines of those investigated by the Road Research Laboratory, but the problem of spray from cars is muchless tractable. -ibis, very briefly, is the essence of the report which the Laboratory submitted to the Society of Motor Manufacturers and Traders and on which the Ministry of Transport has had an interim repl■ from the SMMT (see letters on page 77 of this issue).
The RM. report, submitted early this year. recorded the investigation Of factors influencing the amount of spray thrown up by vehicles on wet roads. in the tests, the effectiveness of mudflaps or other devices was expressed in terms of the numerical factor by which the spray density was reduced when they were fitted. The amount of spray was determined by weighing the water collected on paper ahsorhers mounted on the front of a car travelling behind the test vehicle.
The " splash from the wheels was collected in bottles attached to the vehicle producing the splash.
Speed, tyre-tread pattern and road surface were examined for their effect. On both commercials and cars the spray increased very rapidly with speed. Above 45 m.p.h. the density was proportional to the 2-8th power of the speed— that is. density doubled for a 28 per cent increase in speed—while the amount of spray collected per second by a following car increased much faster, being proportional to the 3-8th power (doubling with a 20 per cent increase in speed).
Neither tread pattern nor road surface (with one exception) made any large difference to the spray generated; the exception was a macadam carpet which, being vert porous. had no standing water —but the RRL added that such surfaces were not et satisfactory' as they either lacked durabilityor lost porosity in use.
The Laboratory found that lorry mudflaps with ground clearances of 8 in. behind all wheels reduced spray density by a factor of between three and four at 50 m.p.h. _A valance overlapping the tyre around its circumference was effective in eliminating the • fine spray 'emerging between mudguard and -tyre. • .
The spray density 30 ft. behind private cars proved to be virtually independent of body size and tyre condition, being affected most by the shape of the rear of the vehicle. Rigid mudflaps behind the back wheels had a [Milted usefulness, especially at speed. While flaps behind the front wheels had little effect and flexible flaps became deflected backwards.
Other ways of tackling the problem were studied: a bonnet-mounted deflector 1-educed the spray striking the windscreen by a factor of up to 10. while the
Laboratory suggested • that further improvements might be looked for in better-drained roads and possibly more elaborate types of mudguard.