Speedo Recalibration Options
Q I am looking into purchasing a used Jeep Wrangler-either a TJ, LJ, or JK. I hope to install a small lift to accommodate larger tires, probably 33s. I know there are a variety of axle gear ratios available in these models. The Rubicon package includes 4.10:1 gears. If I were to add a lift and larger tires to the Rubicon with an automatic transmission, would the transmission need other modifications to ensure the vehicle has plenty of power for the highway and shifts correctly? I do not want the automatic transmission to have issues searching for the right gear.
With a manual transmission, I don't see any issues, but I don't know about what problems I might cause with the automatic transmission. I want to save money and not have to re-gear the axles. Besides changing the speedometer gear to match the tire size, will I need to purchase a programmer also? This vehicle will be a daily driver and see much more street use than off-road use.
A Yep, you're right-you will have to correct your speedometer reading, and you cannot do it with a speedometer gear change. You have two choices. Compare your speedometer reading with that of a GPS unit, and keep track of the percentage difference and do the quick math in your head when you want an accurate reading. The second is to buy a controller that will fix the problem. Superlift (www.superlift.com) has what is called a TruSpeed box, and Pro Comp (www.4wheelparts.com) has a Power Pro Performance tuner that will not only correct the speedometer but also allow you to adjust shift points on the auto trans and even get about 13 more horsepower out of the engine. Your transmission will do just fine as it is.
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