Tire marked radius (rw)M :
Tire size = 225/55R17 ………………
= (W [mm])/ (100H/ W) R (D [in]) …….
From the above definition
W = 225 [mm]
100 H/W = 55
H = 55 W / 100 = 55 x 225 /100 = 123.75 mm
Tire diameter (d) = H + D + H = 2H + D
= ( 2 H + D x 25.4) / 1000 [m]
= (2 x 123.75 + 17 x 25.4) / 1000 [m]
= 0.6793 [m]
Tire free radius (rw)F = d/2 = 0.6793/2 = 0.3896 [m]
Tire free radius (rw)F:
Tire free radius (rw)F = X / 2
Tire static radius (rw)S :
Measure the tire radius from the center of the wheel to the ground
Tire static radius (rw)S = y
Tire rolling radius (rw)R :
a) Put a mark on the tire, put the car on neutral and push the car. Measure the distance car will travel (L) for (n) tire revolutions.
L = n x (2prw)
Tire rolling radius (rw)R = L / (n x 2p) [no tractive effort]
b) Put a mark on the tire, put the car in first gear and drive the car slowly. Measure the distance the car will travel (L’) for (n) tire revolutions.
L’ = n x (2prw)
Tire rolling radius (rw)R’ = L’ / (n x 2p) [with tractive effort]
Report No. 1
Write down the car make & model.
Write down the tire brand & name.
Write down the tire's size of your car.
Explain each marking.
Calculate the tire marked radius.
a- tire free radius,
b- static radius,
c- rolling radius
i- without tractive effort,
ii- with tractive effort.
Write down the tire maximum inflation pressure.
Write down the recommended tire inflation pressures (front, rear).
Find from the tire sidewall markings: the tire load index and write down the maximum load the tire can carry.
Find from the tire sidewall markings: the tire speed markings and write down the maximum car speed the car can travel with this tire.