Calculators:
https://www.ford-trucks.com/calculat.../p-tire_sizes/
https://www.ford-trucks.com/calculat...php/p-mph_rpm/
https://www.ford-trucks.com/calculat...ll_gear_ratio/
More Calculators:
https://www.ford-trucks.com/calculators/index.php

Formulas for MPH RPM gears & tires:
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mph = (rpm x tire diameter) / (gear ratio x 336)

rpm = (mph x gear ratio x 336) / tire daimeter

With OD, rpm = [(mph x gear ratio x 336) / tire daimeter] / O.D. ratio
Example: rpm = [(60 x 3.07 x336) / 31.5] / 1.20 = 1637
-This OD formula added to list-

gear ratio = (rpm x tire diameter) / (mph x 336)

tire diameter = (mph x gear ratio x 336) / rpm

Formulas for tire size & their effect:
---------------------------------------------
effective ratio = (old tire diameter / new tire diameter) x original ratio

actual mph = (new tire diameter / old tire diameter) x actual mph


More info:
====================
RUNNING TIRE DIAMETER IS CLOSE TO THE FULL DIA OF AN INFLATED TIRE
THE STATIC LOADED RADIUS IS MUCH SHORTER THAN THE FULL RADIUS...
USE THE FULL DIAMETER OF THE TIRE MINUS A LITTLE...

TIRE DIA = [((SECTION WIDTH * 2) * (ASPECT RATIO%)) / 24.5] + (WHEEL DIA)
Examples: [(235 * 2 * .75)/24.5] + 15 FOR A 235/75R15
265/75R16 YIELDS => 32.2 DIA W/3.07 = 1934@60 & 2256@70

TO ESTIMATE PROPER PERFORMANCE GEAR RATIO = 0.12 * TIRE DIA
TO ESTIMATE PROPER ECONOMY GEAR RATIO = 0.096 * TIRE DIA

ENGINE RPM @ 60 MPH:::::::::::::::::::::::::::::::::::::::::::::::
-----,------------------ TIRE DIAMETER (INCHES) ----------------------
RATIO|.26....27....28....29....30....31....32....3 3....34....35....36....38....40
-----|-----------------------------------------------------------------
2.73 | 2117 2038 1966 1898 1835 1775 1720 1668 1619 1572 1529 1448 1376
2.90 | 2249 2165 2088 2016 1949 1886 1827 1772 1720 1670 1624 1539 1462
3.07 | 2380 2292 2210 2134 2063 1996 1934 1875 1820 1768 1719 1629 1547
3.21 | 2489 2397 2311 2232 2157 2088 2022 1961 1903 1849 1798 1703 1618
3.31 | 2567 2471 2383 2301 2224 2153 2085 2022 1963 1907 1854 1756 1668
3.40 | 2636 2539 2448 2364 2285 2211 2142 2077 2016 1958 1904 1804 1714
3.54 | 2745 2643 2549 2461 2379 2302 2230 2163 2099 2039 1982 1878 1784
3.73 | 2892 2785 2686 2593 2507 2426 2350 2279 2212 2148 2089 1979 1880
3.90 | 3024 2912 2808 2711 2621 2536 2457 2383 2312 2246 2184 2069 1966
4.09 | 3171 3054 2945 2843 2748 2660 2577 2499 2425 2356 2290 2170 2061
4.56 | 3536 3406 3283 3170 3064 2965 2873 2786 2704 2627 2554 2419 2298
4.88 | 3784 3644 3514 3392 3279 3174 3074 2981 2894 2811 2733 2589 2460
5.12 | 3970 3823 3686 3559 3441 3330 3226 3128 3036 2949 2867 2716 2580
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