Quote:
Originally Posted by Old Tele man
FWIW, in reality, the mathematical tyre diameter and rolling tyre diameter are NOT the same. The mathematical diameter does NOT account for vehicle weight-loading, which slightly flattens the tyre bottom, and thus slightly reduces the actual rolling diameter by about 3%. A good approximation is:
Dia(rolling) ≈ 0.97*Dia(math)
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I never would have thought about that mattering, and I got curious so I did a 2 minute research session. According to
Michelin :
The SAE procedure recognizes that within the test method itself there will be some variation. In fact, there are other factors that cause variation on Tire Revs./Miles among similar tires. Be aware that just because similar tires have the same overall diameter this does not necessarily mean that they will have the same Tire Revs./Mile. The SAE procedure determines the Tire Revs./Mile to within ± 1.5%. Some factors, which cause variation among tires, are: • Load and Pressure – A difference in Load/Pressure could alter the Tire Revs./Mile measurement by as much as 1.5%. If pressure is constant, going from an empty vehicle to a fully loaded vehicle can change the Tire Revs./Mile by 1 to 1.5%. • Treadwear – The Tire Revs./Mile varies from a new tire to a fully worn tire. This can affect Tire Revs./Mile by as much as 3% from the rated Tire Revs./Mile. • Tread Geometry – The height and stiffness of the blocks and the shape of the tread pattern can affect Tire Revs./Mile. • Torque – The presence of driving and braking torque can affect the Tire Revs./Mile. • Type and Condition of Pavement – Asphalt vs. concrete, wet vs. dry can create difference in Tire Revs./Mile.