I've got a 2008 4dr automatic with the 3.73's, 35's, and a 2.5" BB. Like the many posts I'm reading, I've got the horrible constant downshifting on the highway just to maintain speed over rolling hills. My vehicle is definately a daily driver, and I don't intend to do anything overly hardcore...just the monthly weekend trips, and try not to get sucked into too much peer pressure.

I've thought about a cheap upgrade to 4.10's, but will that be enough to overcome the highway downshifting? What gear would be enough to get me past the annoying shifting, yet not cut into my gas mileage too much?

 

If it were me I would probly go with 4.56 or 4.88 gearing, since you have 35" tires 4.88. I have a Rubi with 4.10 and am going to go to 35s and 4.88s.

 

I'm sure you'll get as many opinions as there are options. I personally went with 5.13's and have ABSOLUTELY NO regrets. I use mine as a daily driver and am extremely pleased. And in no way shape or form are the 5.13's over kill. Believe me you WILL NOT be dissappointed.

 

What size tires do you have, and what are your RPMs at 60, 70, and 80 mph?

 

I'm curious as to what your gas mileage is like now? I'm thinking of 35s w/ 3.73s as well. I would eventually regear, but I'd like to know what I'm in for!

 

Just put on my 35's on Friday, have not had a chance to drive it much. So far my 4.10s seem to be ok, but if you are going to regear, then go with the 5.13. I really like the looks of my 35s, but if you want economy, you might want to stay with stock.

 

Shrockworks put together a nice little spreadsheet that helps you determine what you should do based on engine RPM. The general consensus out there is that if you have an automatic and 35" go with 5.13 and if you had a manual go with 4.88. It's still debatable though.

Here's a link to the spreadsheet on my skydrive:
http://cid-aa4d5756727fb33c.skydrive...RPM-Table.xlsx

 

My gas mileage...VARIES...the computer shows me getting 15-16.5 around town, not driving real easy, but not driving it hard either. Cruising the highway that is flat or slightly downhill gives me great mileage, and I can get up past 80mph before my RPMs cross 2000, BUT the second the road starts to incline a little, I start slowing down. I am unable to maintain speed unless I make it downshift, and that kicks the RPMs up close to 2800 or higher. Keeping my speed up is impossible from about 60 and up without the downshifting.

(My RPMs after 35s were added dropped to around 1550~1600 versus the OEM 2000 at about 70mph.)

Now, if you want to drive extremely easy on the vehicle...about a month ago I took a weekend trip that was about 200 miles away and was all highway without hardly any stops thru small towns. I was following a buddy pulling his CJ on a large trailer, so he was trying to be light on the gas usage. On that trip, I drove the whole way down without downshifting on the highway, and letting the speed fluctuate between 50~75 the whole time. The onboard computer showed 21.3mpg when I arrived.

I bet I could get closer to 17+ around town today if I drove a little easier, but my daily commute is only 15 miles, and I spend a good amount waiting on lights, and doing stop and go driving which kills the mileage.

My main concern is getting enough gear to stop needing it to downshift so much on the highway. This alone will increase my mileage enough to offset the bigger gear. I just don't want too big a gear to raise my RPMs past what they need to be to get over this highway need.

 

If you want to bring your JK back to stock performance, 4.88's are what you will want. However, as several others had mentioned, you will be much happier with 5.13's as they will give your Jeep what feels like 30 extra HP. I did it and loved it.

 

4.56 and 35's would be like a rubi with 4.10 and 32's
4.88 and 37's would be like a rubi with 4.10 and 32's
5.13 and 40's would be like a rubi with 4.10 and 32's


now for you, with the 3.73 gears stock and i'm assuming 32" tires stock. to get the same power level and milage from the 35's that you had with 32's, you'd need 4.10 gears.

now... add the small amount of extra weight from the lift, then a bumper, winch, etc, and you might as well go a step up. so if you have 35's and have a bunch of extras, get the 4.56. your high way milage will suffer, but you'll have better then stock pickup power even with all the stuff on your jeep.