What size Lift? What size Tires?

The Formula

2242 = 65 x 3.08 x 336 / 30

To use an example, let's say we want to know what gears should be installed when putting 36" tires on a transmission, 3.08 gears, and 30" tires in stock form. Since the truck doesn't have a tach, we first need to find out what RPM the engine is spinning at a given speed, say 65 mph. With this information, the formula looks like this:

rpm = mph x gear ratio x 336 / tire diameter

At 65 mph, the truck's engine is spinning at 2242 rpm, which is right in the optimum powerband for most V-8 engines. Now all that's left to do is plug in the new tire size and a couple different ratios available for the truck to see which one closely matches the RPM.

2263 = 65 x 3.73 x 336 / 36

As you can see from the above formula, 3.73 gears with 36" tires is optimum for restoring stock performance with this truck. Keep in mind that not all ratios are available for every axle, so do some research to make sure there's a ratio close to what you need available for your truck's axles.

One last note regarding trucks equipped with overdrive. The Overdrive gear in a transmission allows the drivetrain to run below a 1:1 ratio, which brings down engine RPM for good fuel economy when running down the highway. Most Overdrive gears run somewhere around 0.73:1. As we said before, the best option for people who use the truck primarily on the street is to match the formula given above.

However, Overdrive offers a unique opportunity for dedicated off-roaders. Since overdrive decreases the reduction at highway speeds, it's possible to "cheat" and select gears that are a little lower (numerically higher) for better slow gearing off-road without sacrificing highway drivability. This advantage becomes apparent when you do the math by multiplying a prospective gear ratio by the Overdrive ratio of your transmission.

To use an example, 5.13 gears in a truck without an overdrive and moderate-sized tires would offer awesome slow-speed crawling ability for off-road situations but would leave the engine screaming at highway speeds. However, if the same 5.13s are installed in a truck equipped with an overdrive of 0.73:1 and we do the math (5.13 x 0.73 = 3.744), we find that the Overdrive gear gives the effect of a very streetable 3.73 ratio for highway cruising. In other words, the truck has the same good crawling speed of 5.13 gears (because Overdrive is never used off-road) combined with a very street-friendly effective ratio of 3.73 gears. Of course the engine will still rev higher on the highway compared to having the proper ratios found by following the steps we laid out earlier. Overdrive does offer dedicated four-wheelers the option of installing low, off-road friendly gears and still be able to drive around on the street with some fuel economy left intact. To plug overdrive into the gearing formula above, simply multiply the Overdrive ratio by the axle gear ratio.

This article was presented by SuperLift to help answer any questions you might have about lift kits. If you need more information, please call 4 Wheel Online toll free at 1-813-769-2451, or visit our website at http://www.4wheelonline.com/?SuperLift_Suspension.

This chart helped me with my set up when I first started hope it helps u.

Here is another site that can help, also can determine your final crawl ratio.

http://www.4lo.com/calc/gearratio.htm