I have a 2006 TJ with 4.0 engine and the 42rle automatic trans. I just changed my tires and wheels from 15" wheels with 31x10.5x15 tires to Moab 16" wheels with 31.5" x10.5 tires. I have not seen a huge difference driving it around town, but I am wondering if the taller 31.5 tires are ok with the auto trans and 3.73 axle gears. Looks like a lot of people put 33" tires on this set up without any problems. When I am going faster. like 60 mph the RPM seem to drop further. I don't know much technical info, but I assumed the Over Drive was kicking in and the RPMs with the taller tires drops more than before. I slo note that I have a dashboard switch that turns the Over Drive off. Should I turn off the over drive at higher speeds to keep the RPM a bit higher? Some may think my questions a dumb and that may well be true as I am not well educated on Jeep gearing and tire size effects. Thanks in advance for any info. I don't think it woul dbe worth it to spend over $1,000 to go to 4.10 gears but I know that would be best.
Changed to 16 inch wheels with 31.5 inch tires
- Thread starter Peter Panagakos
- Start date
The larger the tire's diameter, the slower the engine turns at any given speed. At certain speeds the engine rpms may be turning slower than is optimal for power and mpg so turning the overdrive off can be very helpful... especially with your 42RLE's very steep overdrive that is very prone to dropping the rpms too low too easily. Turning the OD off is commonly done and not a bad idea. Regearing to 4.56 wouldn't be a bad idea if that amount of $$$ wouldn't be missed from your checking account. 4.10 is barely enough, 4.56 would be better for the highway. Or even to a lower ratio if you think you'd even get to 33's or 35's. I had to go from 4.88 to 5.38 for my 35" tires which cured many problems and even improved the mpg from <12 to >14 mpg.