Efficiency is the tyre's capacity to DELIVER THE ENERGY supplied by the cyclist in riding conditions.
Efficiency is expressed by the following formula: (energy delivered) / (energy supplied) = Efficiency.
As this formula always gives a result of less than 1, efficiency is therefore always expressed as a value between 0.00 and 0.99.
FOR THE TYRE PART, EFFICIENCY DEPENDS ON:
the nature of the rubber compound (presence of silica, ...)
the tread pattern
the density and construction of the fabrics (TPI, or number of threads per inch)
the architecture of the tyre, the reinforcements, …
the quality of the inner tubes used (MICHELIN :Latex>UltraLight>AirStop>Protek)
the tyre size (23>20>...)
the inflation pressure (8>7>6bars ...)
the tyre's rolling resistance
THERE ARE OTHER EXTERNAL FACTORS AFFECTING EFFICIENCY:
the nature of the road surface
aerodynamics
wheels and bearings