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GEAR RATIO GUIDE
Click here for Speedo Gear Info

Gear Ratio Formula:
(New tire size / Stock tire size) x Original gear ratio 
To find out tire size if you have metric tires:;
 225/75R14 = 26.5" 	27x8.50R14
 215/75R15 = 27.5"
 235/75R15 = 28.5" 	29X9.50R15
 245/75R15 = 29.5" 	30X9.50R15
 265/75R16 = 30.5" 	31X10.50R15
 295/75R15 = 31.5" 	32X11.50R15
 315/70R15 = 32.5" 	33X12.50R15
 285/75-16 = 32.8" 	33X12.50R16
To find out your gear ratio:
 Open differential 	Limited slip
      72-3.08 		  F4-3.45
      74-3.45 		  F5-3.55
      82-3.08 		  F6-3.73
      84-3.45 		  F7-4.10
      85-3.55 		  K6-4.10
      86-3.73
      87-4.10
      91-3.27
      96-3.73
Purple indicates highway driving & good fuel economy.
Green indicates Daily driver & bestoverall performance.
Red indicates towing and power. Reduced fuel economy.

2.35 2.73 2.94 3.07 3.21 3.31 3.42 3.55 3.73 3.91 4.11 4.27 4.56 4.88 5.13 5.29 5.38 5.71 6.17 7.17
23" 2231 2592 2792 2915 3048 3143 3248 3371 3542 3713 3903 4055 4330 4634 4871 5023 5109 5422 5859 6808
24" 2139 2484 2675 2794 2921 3012 3112 3231 3394 3558 3740 3886 4150 4441 4668 4814 4896 5196 5615 6525
25" 2053 2385 2568 2682 2804 2892 2988 3101 3259 3416 3590 3730 3984 4263 4482 4621 4700 4988 5390 6264
26" 1974 2293 2470 2579 2696 2780 2873 2982 3133 3284 3452 3587 3830 4099 4309 4444 4519 4796 5183 6023
27" 1901 2208 2378 2483 2597 2677 2766 2872 3017 3163 3325 3454 3689 3947 4150 4279 4352 4619 4991 5800
28" 1833 2129 2293 2395 2504 2582 2668 2769 2909 3050 3206 3331 3557 3806 4001 4126 4196 4454 4813 5593
29" 1770 2056 2214 2312 2417 2493 2576 2674 2809 2945 3095 3216 3434 3675 3863 3984 4052 4300 4647 5400
30" 1711 1987 2140 2235 2337 2410 2490 2584 2715 2846 2992 3109 3320 3553 3735 3851 3917 4157 4492 5220
31" 1656 1923 2071 2163 2261 2332 2409 2501 2628 2755 2896 3008 3213 3438 3614 3727 3790 4023 4347 5051
32" 1604 1863 2007 2095 2191 2259 2334 2423 2546 2669 2805 2914 3112 3331 3501 3610 3672 3897 4211 4894
33" 1555 1807 1946 2032 2124 2191 2263 2349 2469 2588 2720 2826 3018 3230 3395 3501 3561 3779 4083 4745
34" 1510 1754 1889 1972 2062 2126 2197 2280 2396 2512 2640 2743 2929 3135 3295 3398 3456 3668 3963 4606
35" 1466 1704 1835 1916 2003 2065 2134 2215 2328 2440 2565 2664 2845 3045 3201 3301 3357 3563 3850 4474
36" 1426 1656 1784 1862 1947 2008 2075 2154 2263 2372 2493 2590 2766 2961 3112 3209 3264 3464 3743 4350
37" 1387 1611 1735 1812 1895 1954 2019 2095 2202 2308 2426 2520 2692 2881 3028 3123 3176 3370 3642 4232
38" 1351 1569 1690 1764 1845 1902 1966 2040 2144 2247 2362 2454 2621 2805 2948 3040 3092 3282 3546 4121
39" 1316 1529 1646 1719 1798 1854 1915 1988 2089 2190 2302 2391 2554 2733 2873 2962 3013 3198 3455 4015
40" 1283 1491 1605 1676 1753 1807 1867 1938 2037 2135 2244 2331 2490 2664 2801 2888 2937 3118 3369 3915
41" 1252 1454 1566 1635 1710 1763 1822 1891 1987 2083 2189 2275 2429 2599 2733 2818 2866 3042 3287 3819
42" 1222 1420 1529 1596 1669 1721 1778 1846 1940 2033 2137 2220 2371 2538 2668 2751 2798 2969 3208 3728
43" 1194 1387 1493 1559 1630 1681 1737 1803 1894 1986 2087 2169 2316 2479 2606 2687 2733 2900 3134 3642
44" 1166 1355 1459 1524 1593 1643 1698 1762 1851 1941 2040 2119 2263 2422 2546 2626 2670 2834 3063 3559

65 mph in 4th gear w/ manual transmission. Automatic transmission RPM is higher than shown above.
With overdrive, your RPM is 15-30 % less than RPM value above.
This info was taken from 4 Wheel Parts Wholesaler Catalog.

CHANGING THE SPEEDO GEAR
When you change tire size or gear ratio, your speedometer reads inaccurately.
To fix this you have to change speedo gear(change number of teeth).
1st, you need to find out current speedo gear(# of teeth).
You have to remove the speedo cable from trans to check what you have(instruction below).

Ford Speedo Gear Parts #
Manual Trans Auto Trans
16-teeth-wine (C0DZ-A) 16-blue (D0AZ-A)
17-white (C3DZ-C) 17-green (C7SZ-A)
18-yellow (C0DD-B) 18-gray (C7SZ-B)
19-pink (C0DZ-B) 19-tan (C7VY-A)
20-black (C1DZ-A) 20-orange (C8SZ-B)
21-red (C4OZ-A) 21-purple (D0OZ-B)


Then use the formula.

New teeth = (current teeth x speedo reading) / actual speed.

You need less teeth to speed up the speedometer. (More teeth to slow down speedometer.)
Then go to Ford and get the speedo gear that you figured out.
To install or remove, go under the truck and find transmission.
Near the end of the trans (driver's side) there should be a black cable
that is about 1 cm in diameter. It should be attached with one bolt and
small bracket; remove the bolt. Pull the cable straight from trans.

You will be able to see the gear now.
The gear is attached to the cable with a small clip;
remove it with small screw driver and remove old gear.
Put new one on and rest is just backward.

If the O ring around the cable assembly is bad, replace with new one.
I changed mine few month ago, but it was 2WD manual, not 4X4, so lacation or
style of mounting the speedo cable may be different.
Speedo reading will NOT be accurate as it used to if you change tire size(but close).

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