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The diagram
below shows the effect of wheel diameter and tire pressure on the rolling
resistance. Air resistance of the bike and rider has been included in the
overall power needed at two speeds, 25 mph (11.2 m/s) and 12.5 mph (13.4 m/s).
It is seen that the effect of wheel diameter favors the larger wheel and
that tire pressures larger than about 4 atm (4 x 105 Pa) provide
little additional reduction in rolling resistance. It is also clear that aerodynamic
drag dominates power loss at the higher speed. Rolling resistance itself
is not a strong function of wheel speed and, therefore, the power dissipated
by this loss mechanism depends linearly on the speed. |
