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| TIRE/ GEAR SIZE CHART |
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It is your responsibility to insure that the information is correct for your application.
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Gear Ratio Guide For Larger Tires |
When ever you change tire size from the original size to another there will be a direct effect on power and drivability. We have developed this chart to help you select the optimum gear ratio to put your performance back where you want it.
If you are interested in a change that will give more power or better fuel mileage use the color coding as a guide.
A simple formula
The most simple formula for the correct gear ratio is this:
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New Tire Size x Old Gear Ratio |
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New Gear Ratio = |
――――――――――――――――― |
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Old Tire Size |
Example:
The original tire size is 30" and the original gear ratio is 3.91. You plan on moving up to 38". Then the formula would be calculated as: (38*3.91)/30 giving you 4.95. Not all gear ratios are available so you have the choice between 4.88 and 5.13, 4.88 being the closest.
Choose a little bit lower gear ratios if you do a lot of off-road driving and a little bit higher if you do more long distance highway trips.
This chart is based on 65 MPH and a 1:1 gear ratio, on manual transmission (4th gear). Please NOTE: If your vehicle is equipped with an automatic transmission the RPM wil be higher than shown on the chart, because some slippage will occur in the transmission and torque converter. With overdrive transmission, your RPM in overdrive will be 15 - 30% less than indicated, depending on the vehicle.
RPM Chart
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Highway Driving, Good Fuel Economy |
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Daily Driver, Best Overall Performace |
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Towing and Power, Reduced Fuel Economy |
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Gear Ratio |
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Tire |
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2.73 |
3.07 |
3.55 |
3.73 |
4.11 |
4.27 |
4.56 |
4.88 |
5.13 |
5.29 |
5.38 |
5.71 |
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28" |
2129 |
2395 |
2769 |
2909 |
3206 |
3331 |
3557 |
3806 |
4001 |
4126 |
4196 |
4454 |
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29" |
2056 |
2312 |
2674 |
2809 |
3095 |
3216 |
3434 |
3675 |
3863 |
3984 |
4052 |
4300 |
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30" |
1987 |
2235 |
2584 |
2715 |
2992 |
3109 |
3320 |
3553 |
3735 |
3851 |
3917 |
4157 |
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31" |
1923 |
2163 |
2501 |
2628 |
2896 |
3008 |
3213 |
3438 |
3614 |
3727 |
3790 |
4023 |
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32" |
1863 |
2095 |
2423 |
2548 |
2805 |
2914 |
3112 |
3331 |
3501 |
3610 |
3672 |
3897 |
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33" |
1807 |
2032 |
2349 |
2489 |
2720 |
2826 |
3018 |
3230 |
3395 |
3501 |
3561 |
3779 |
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34" |
1754 |
1972 |
2280 |
2396 |
2640 |
2743 |
2929 |
3135 |
3295 |
3398 |
3456 |
3668 |
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35" |
1704 |
1916 |
2215 |
2328 |
2565 |
2664 |
2845 |
3045 |
3201 |
3301 |
3357 |
3563 |
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36" |
1656 |
1862 |
2154 |
2263 |
2493 |
2590 |
2766 |
2961 |
3112 |
3209 |
3264 |
3464 |
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37" |
1611 |
1812 |
2095 |
2202 |
2426 |
2520 |
2692 |
2881 |
3028 |
3123 |
3176 |
3370 |
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38" |
1569 |
1784 |
2040 |
2144 |
2362 |
2454 |
2621 |
2805 |
2948 |
3040 |
3092 |
3282 |
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39" |
1529 |
1719 |
1988 |
2089 |
2303 |
2391 |
2554 |
2733 |
2873 |
2962 |
3013 |
3198 |
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40" |
1491 |
1676 |
1938 |
2037 |
2244 |
2331 |
2490 |
2664 |
2801 |
2888 |
2937 |
3118 |
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41" |
1454 |
1635 |
1891 |
1987 |
2189 |
2275 |
2429 |
2599 |
2733 |
2818 |
2866 |
3042 |
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42" |
1420 |
1596 |
1846 |
1940 |
2137 |
2220 |
2371 |
2538 |
2668 |
2751 |
2798 |
2969 |
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43" |
1387 |
1559 |
1803 |
1894 |
2087 |
2169 |
2316 |
2479 |
2606 |
2687 |
2733 |
2900 |
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44" |
1355 |
1524 |
1762 |
1851 |
2040 |
2219 |
2263 |
2422 |
2546 |
2626 |
2670 |
2834 |
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