4x4 Gear Ratios | Selecting the right gear ratios!

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In this video I will tell you about gear ratios for your 4x4 truck and how to choose the best gear ratios.

Lets begin with looking at the big picture.

Just like a car a 4x4 has an engine and a transmission. In addition it has a transfer case

moving pover front and rear.

Taking my own 4x4 as an example it has a transmission with the lowest gear of 2.47 and the 4Lo is 2.48. My differentials are 4.88.

Multiplying these three ratios gives me the overall gear ratio or crawl ratio of 29.77 - a reasonably low number for a 4x4 with an automatic transmission.

When getting bigger tires for your 4x4 it is easiest to change the gear ratio in the differential.

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Tire Size Calculation

When you plan on getting bigger tires you have to figure out a new gear ratio for your differentials.

This is both for performance as well as fuel economy.

You begin with multipling your new tire size with your old gear ratio and dividing the result with the old tire size.

This is a simple formula that gives a pretty accurate result.

Continuing with the example I multiply 38 with 3.91 and divide the result with 30 giving me the number 4.95 where the closest awailable gear ratio is 4.88.

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Differential Gear Ratio

The gear ratio most interesting to 4x4 truck owners is the ratio between the driveshaft and axels. It is controlled by the number of teeth in the ring vs. the pinion.

Lets look at these two perfectly rount gears. The smaller one is the driving gear and the larger the driven gear.

If the smaller one has 10 teeth and the bigger one 20 the gear ratio between them are 20 to 10 or 2 to 1.

The differential works in the same way except the directions of the axles are at a 90° angle.

So the pinion is an extension of the driveshaft and the ring is around the axles.

In this case the pinion has 8 teeth and the ring 39 teeth. Dividing gives us the real ratio 4.875

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Also feel free to comment on the video and you are welcome to suggest other topics of interest.

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