RUSTYS
Well-Known Member
LMAO!The best source of info are Jeep Engineers and lift shops. If you move to 35" tires, they recommend 4.56, if going to 37s at a minimum 4.88, but 5.13 is preferred. The stock gearing - even Rubicon- does NOT ( I repeat NOT) support 35s. If you do not re-gear, the speedo will be off and MPG will take a major hit unless you buy a programmer. Its all about wear and tear so if you plan to keep your Jeep and throw tires on that arent supported, then to do it right, re-gear. If you want to have a better shot at warranty coverage, do the Mopar lift and the Mopar gears (they are now available). More money, but OEM is always better IMO.
To test this theory, I have 35s and the stock 3.45 gears - programmed. My RPMs went higher at speed and my MPH took a 2MPG hit. I re-geared to 4.56 just recently and the MPG climbed, RPMs dropped and I can actually getting into the higher gears on the freeway now. That and my Driveshaft no longer is taking extra stress.
You can ask random people in forums (these are the people here who say, "yea just throw on big tires on stock gears...runs fine" - yikes) or ask experts who either do this for a living / take advice from ones that engineered the JL - I know who I pick.
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