Tire Size and Effective Gear Ratio

rev/mi for old vs new tires, effective ratio, cruise speed, recommended axle ratio.

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Formula and source

Effective tire diameter from metric size (e.g., 285/75R17): D_in = (W_mm × ratio/100 × 2 + R_in × 25.4) / 25.4. Revs/mile = 63 360 / (π × D). Effective ratio = axle_ratio × (rev/mi_stock / rev/mi_new).

Tire & Rim Association (TRA) Yearbook by name; ETRTO Standards Manual by name; SAE J267 metric-tire size convention.

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