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MPH |
65 |
Remember non of these calculations account for torque converter slippage
RPM formula used = (MPH*Trany*rear*336)/tire diam |
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Trany Gear |
0.7 |
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265/60/18 |
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w/wear |
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RPM Chart |
225/70/17 |
235/70/17 |
245/70/17 |
255/70/17 |
275/65/18 |
285/70/17 |
Calculated |
BFG spec |
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Gear/Tire hight |
29.3 |
30 |
30.5 |
31 |
32 |
32.5 |
32.7 |
32.8 |
34 |
35 |
36 |
37 |
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3.33 |
1738 |
1697 |
1669 |
1642 |
1591 |
1566 |
1557 |
1552 |
1497 |
1455 |
1414 |
1376 |
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3.55 |
1852 |
1809 |
1779 |
1751 |
1696 |
1670 |
1660 |
1655 |
1596 |
1551 |
1508 |
1467 |
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3.73 |
1946 |
1901 |
1870 |
1839 |
1782 |
1755 |
1744 |
1739 |
1677 |
1629 |
1584 |
1541 |
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4.1 |
2139 |
2089 |
2055 |
2022 |
1959 |
1929 |
1917 |
1911 |
1844 |
1791 |
1741 |
1694 |
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4.3 |
2244 |
2191 |
2155 |
2121 |
2054 |
2023 |
2010 |
2004 |
1933 |
1878 |
1826 |
1777 |
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4.56 |
2379 |
2324 |
2286 |
2249 |
2179 |
2145 |
2132 |
2125 |
2050 |
1992 |
1936 |
1884 |
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4.88 |
2546 |
2487 |
2446 |
2407 |
2331 |
2296 |
2282 |
2275 |
2194 |
2132 |
2072 |
2016 |
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Here's what some of the colors mean: |
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30" tire is base stock with 3.55 & 3.73 option |
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30.5" tire as listed with 4.10 payload pkg option |
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31" tire is my stock with 3.55 & 3.73 option |
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31" & 32" tires are stock on 3.73 fx4 |
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32.5" if worn, 32.8 on BFG specs and 32.7 calculated for my tires |
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After gear change RPM increase 4.56 vs my stock & Ford eng'd tow pkg |
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33" My tires |
32.7 |
Over % |
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Stock |
323 |
18% |
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Tow pkg 4.10 |
77 |
4% |
Ford engineered a combination for towing; 4.56's get me just a touch
better |
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PreGear w/tire |
472 |
27% |
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RPM decrease with tire change vs ford eng'd stock 31" & 30" tires and
tow pkg |
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33" My tires |
32.7 |
Loss % |
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Stock |
-91 |
-5% |
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Base Stock |
-149 |
-9% |
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Tow pkg 4.10 |
-395 |
-19% |
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With 4.56 gears and 32.5+" tire the effective final ratio comparison is
pretty much just like a 4.10 |
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Final drive ratio |
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Diff 3.55 |
Diff 4.10 |
Diff 4.56 |
increase |
w/Tires vs stock |
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1st |
2.84 |
10.08 |
11.64 |
12.95 |
2.87 |
1.56 |
In a higer tq&hp band sooner |
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2nd |
1.55 |
5.50 |
6.36 |
7.07 |
1.57 |
0.85 |
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3rd |
1 |
3.55 |
4.10 |
4.56 |
1.01 |
0.55 |
18% more power xfer vs stock? |
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4th OD |
0.7 |
2.49 |
2.87 |
3.19 |
0.71 |
0.39 |
4% more power xfer vs stock tow? |
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If FOMOCo could callibrate me for a 225/70/17 tire and 4.10 gears it
would get my speedo back near match. |
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