Does this sound right? He says with my 2in lift and 33x12.5 tires (on a 4 door JK), the transmission ratio of 3.78 (stock) won't work correctly. I need to re-gear to 4.10 or so. With the gears as 3.78, the transmission won't perform well off-road and will overheat the cooling system.

I don't know anything about gear ratios, so do those numbers sound correct? Does his logic follow?

Thanks in advance for any advice.

 

This sounds a bit extreme to me. "Won't work correctly", sure it will be more work on the transmission to turn the heavier tires, but I wouldn't say that it wasn't working correctly...unless of course the reason it was in the shop is because it was overheating (which from the thread title could very well be the case).

The Rubicon comes stock with 32" tires and 4:10 gears, so it is true that your Unlimited would be closer to the Chrysler recommended setup if you went with 4:10 gearing...and would obviously perform a bit "better" (more torque and low-end power...but fuel economy would suffer) on and off road.

 

Isn't standard 3.21's with 32's? You would think that would make 33's with 3.78 more than acceptable.

Just my SWAG, and failing memory of standard features, but it seems to me...........

 

mathematically yess there is more strain on the jeep with the taller gear ratio and therefor may cause more heat from the engine... but he is totally wrong in attributing that to the overheating issue. especially if you wheel if 4lo. plenty of us run 33's and lots of us 35... some even 37s on the 4:10 gears and they're not having the over heating issues. I call BS on this due to ignorance on their part. regearing is something you might want to do for power and milage reasons, but its not cheap and not going to solve your problem. i would recommend a tranny cooler to help out...

 

I find that hard to believe. First those 33's aren't much bigger than the stock 32s that come on the X S Package, Sahara, and Rubicon. Also, I don't think and overheating transmission would cause an engine to overheat. At least to the point where you would notice the engine before the transmission.


But for now, I say your dealer is

 

both of my 08's came with 32" tires and 3.73's
I am now running 33 12.5's and having no issues

 

Yeah I'd have to call BS on the dealers explanation. Yes, there is some change with the bigger tires but really 33's shouldn't be that noticeable. I'd check with another dealer if possible. There's something else wrong.

 

I agree-it aint your tires,sounds more like a torque converter issue that is causing the fluid to overheat.

 

i dont think that it is necessary for you to regear with 33's. however, from a performance standpoint you might want to. the general consensus is that for street and offroad performance 4.10's and 33's are the way to go. i have this setup and i think if works very well for what i do.

 

Yes, I took it in for overheating. I've been thinking of adding a tranny cooler after seeing some others doing it on this forum. I'm not really concerned about fuel economy, I just don't like running the heat each time I'm off-road because the coolant temp is rising so high.