I am modding a 2010 jk unlimited sport. I am putting a 2.5 inch lift, 1.5 inch spacers, and 325 terra grapplers. I have a superchips programmer ordered. Do I need to regear? I am currently running 3.73 gears and I found a deal on 4.88 gears.

I have read the charts. This is a DD. Live in a relatively flat area. Mostly around town and off road once a month. I am at about 18 mpg with the stock wheels and no lift. How much will that change with the new gears? I don't mind it going down some but not down a ton. I drive slow but want the power when needed.

 

From what I've read and seen, you'll probably want to regear. Especially if you can get a deal on them. Once you get to tires in the 35"+ range the stock gears on the 3.8L are just not quite up to the job when you really need some power. Not sure how it'd effect your mpg's though I would think it wouldn't be more than a couple mpg difference

 

Is your JK an auto or manual?

It doesn't make a difference in terms of re-gearing, more as to what the appropriate gear set would be.

 

I thought i included that it is an automatic. I must have deleted that portion. Also, this is a 4 door.

 

There are a couple Terra Grapplers in 325s, so I'll assume you are speaking of the ones that measure 35" in diameter. 4.88s might work for you, although I'd get some miles on the new tires first. OD Off will give you a taste of what 5.38s would be like at cruise speeds, and the majority of people who have re-geared in a similar situation will find themselves running 5.13s.

Also, as you're getting a Flashpaq, you might want to also get their advanced Trans Tune package which can give you some more robust shift points.

 

I got the vivid linq.

So I definitely need to get out of the 3.73 gears, just decide if 4.88 is enough? Yes I got the true 35 inch terras

 

OK, Great! With the Vivid Linq you can keep an eye on load with the 3.73s and your 35s. With the trans tune, you can see how far you can push things while feeling comfortable by adjusting the shift point schedules, both with OD on and off. That will give you an excellent basis for making your gear selection.

 

Can you be a little more specific on what I need to pay attention to? I have just enough knowledge to be dangerous.

 

your wallet.... cause there's gonna be spider webs & bats flyin' outta there after your install!

 

There is a power group gauge cluster which will show you load and TP%s. That one is totally key to see what's going on. Pretty much you want your load percentages falling in the 50-75% realm with larger percentages occurring due to wind or grades. If you get below a 50% load you are spinning the engine more than you need to and above 75% it will open your throttle blade enough that you are running a fat fuel mixture in open loop. Most of all, you want to minimize the frequency of downshifts, as they are what robs efficiency the most.