cl = rolling resistance coefficient - dimension length (coefficient of rolling friction) (mm, in)
r = radius of wheel (mm, in)
Some typical rolling coefficients:
|Rolling Resistance Coefficient|
|0.001 - 0.002||0.5||railroad steel wheels on steel rails|
|0.001||bicycle tire on wooden track|
|0.002 - 0.005||low resistance tubeless tires|
|0.002||bicycle tire on concrete|
|0.004||bicycle tire on asphalt road|
|0.005||dirty tram rails|
|0.006 - 0.01||truck tire on asphalt|
|0.008||bicycle tire on rough paved road|
|0.01 - 0.015||ordinary car tires on concrete, new asphalt, cobbles small new|
|0.02||car tires on tar or asphalt|
|0.02||car tires on gravel - rolled new|
|0.03||car tires on cobbles - large worn|
|0.04 - 0.08||car tire on solid sand, gravel loose worn, soil medium hard|
|0.2 - 0.4||car tire on loose sand|
The rolling coefficients for air filled tires on dry roads can be estimated
c = 0.005 + (1 / p) (0.01 + 0.0095 (v / 100)2) (3)
c = rolling coefficient
p = tire pressure (bar)
v = velocity (km/h)
The standard wheel pressure in a Tesla Model 3 is 2.9 bar (42 psi). The rolling friction coefficient at 90 km/h (56 mph) can be calculated from (3) as
c = 0.005 + (1 / (2.9 bar)) (0.01 + 0.0095 ((90 km/h) / 100)2)
Increasing the pressure to 3.5 bar reduces the rolling resitance coefficient to
c = 0.005 + (1 / (3.5 bar)) (0.01 + 0.0095 ((90 km/h) / 100)2)
((0.011 - 0.10) / 0.011) 100% = 9%
The rolling resistance for all four wheels in a car with total weight 1500 kg on asphalt with rolling friction coefficient 0.03 can be estimated with the generic equation 1 as
Fr = 0.03 (1500 kg) (9.81 m/s2)
= 441 N
= 0.44 kN
The rolling resistance for one wheel can be calculated as
Fr = 0.03 (1500 kg / 4) (9.81 m/s2)
= 110 N
= 0.11 kN
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