Oversized tires and overdrive

[DraykenK]

I have 35" tires. The Jeep runs fine, altho a dog. I have not changed gears yet, nor do I know when I will be able to. When I'm doing about 50mph, I'm assuming OD is kicking in, and the RPMs go to about 1,300. My problem is, it is actually a little difficult to kick the jeep out of this. If I slightly step on the gas, it will SLOWLY pick up speed, but stick at 1,300 RPMs. It almost feels like it won't shift. I have to either step on the gas significantly, or let off the gas, then back on, to kick it out of the 1,300 zone. If I turn OFF the OD, then I do not have this problem, so that's why I assume this is all the OD. My question is, is this normal, and just because I'm running 35"? Am I possibly hurting anything? I just want to make sure I'm not doing any harm.

 

[Rob5589]

With that combo, keep it out of OD. Lugging it around at those near idle rpm's are no good on the engine or trans.

 

[Shwane]

+1 on not using your overdrive. There are no TJ configurations from the factory that will run 35's appropriately.

When in this configuration, your engine tends to "lug" Basically your connecting rods are vibrating on the crank. Thus you lose your hydrodynamic lubrication effectiveness or the oil wedge built up in bearings from your crank spinning in them. It puts a lot of stress on the bottom end. It also diminishes your fuel economy by using more fuel to maintain the same speed.

Think of it as trying to take off in 3rd gear compared to first. Which one would require more throttle? Same principle when running larger tires on factory gears.

70 mph on the highway, then ideally rpms should be around 2400-2700. 3000 isn't even terrible, but not ideal just for fuel economy reasons, not mechanical. These engines can run that all day long no problems.

**Edit**
Without knowing your exact set up, being its and auto and 35's I'd go with 5.38's I believe that would get you into the optimal (although pricey) rpm range for highway driving. I believe Mr Jerry just did this swap and loves it. For the life of me I don't know how to tag people in here. But I'm sure he'll see this and chime in.