a Can we road test brake efficiency with a Tapley meter
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in the unladen or partladen state, or must the vehicle be fully laden to its plated gross operating weight? If so can you provide the formulae for calculating the fully laden g factor for Tapley readings taken in the unladen or part laden state. Also who supplies the Tapley meter?
A The C and U Regulations require that
The following example shows how difficult this method would be: a vehicle giving a 50 per cent efficiency when tested at 16 tons would be expected to give a reading of 100 per cent when tested at 8 tons, which is inconceivable without wheel locking.
The Tapley meter is manufactured by Tapley Meters Ltd., Belvedere Works, Commercial Road, Totton, Hants. braking efficiency must be attainable at all times—unladen, part laden or fully laden. So to be sure of passing any surprise test you should obtain the figures for your vehicles in the fully-laden condition.
There is no formula which will allow you to get an accurate efficiency figure for this fullyladen condition from a test carried out part laden. It is possible to do this using equipment such as roller testers which give readings of actual braking efforts at the wheels.
Brake efficiency is braked effort divided by gross vehicle weight times 100 and can be calculated for any desired gross weight. A rough idea can be obtained on a part laden road test with a Tapley meter but factors such as wheel locking, bouncing of the vehicle and so on can have a considerable effect and cause misleading results.
Only if a Tapley reading giving an accurate indication of actual effort at the wheels is obtained can the same calculation be used. So, if a vehicle were tested at 10 tons, a 70 per cent reading with no locking or other misleading factors indicates a total brake effort of 7 tons, which works out at 50 per cent brake efficiency from the same vehicle grossing 14 tons.