Hello guys i'm new here. I was thinking of upgrading my wheels and tires to a 33.5. Therefore I wanted to know what gear ratio I would need to run to get the best perfomance/mpg. My current gears are 3.21 auto 3.6L.

 

Welcome to JKF.. Good Group of JEEPERs here.. .much knowledge and many opinions.. IMO with 33's; living in Co. Given the expense of the change suggest 4.10s .. the jump up from 3.73 isnt that big.. Check Jeep clubs asking for what you are considering and go for a test ride with that geared Jeep. The 3.6L and Auto in JKs with 33s will give you a good example.

 

 

It's just my opinion, but given your location I'd go with 4.56. I have done enough driving in the mountains to just succumb to the idea that you're revving at higher RPMs one way or the other. Better to have some power in 4th and 5th gear than to be limited to 3rd gear climbing the roadways through mountains. My gearing opinions can be all over the map sometimes but generally I think the 3.6L performs decently in that 2700-2800 rpm range on the charts above. Even if your 33.5" tire measures around 32" in the real world, that puts you in that range @ 70mph. I would also add this though, people can hem and haw all day long over one gear set or another. When you're down to either "this" or "that" your consternation is over 100rpm or so. It's not a huge difference and most often either/or gearing will work and be ok. Sometimes you might wish you had the other gearing, sometimes you'll be happy to have what you have. IE, 4.10 would work, 4.56 will give you a bit more power but also bit higher RPMs. Through fuel economy out the window. The difference will be negligible relative to your driving satisfaction.