good thread. In for when I get there

 

So what gear did you decide on? I drive 300 miles one way every two weeks & I get my 285 installed this week.

 

I have not installed gears at this point. I think I am going to go with the 5.13s. With OD off and 3.73s my RPMs at 70 are 2800. With 5.13s, at 70 I would be looking at 2500. So, seems like 5.13s are the right choice.

 

That's what I'm thinking 5.13s also. And I got an email this morning from Superchips saying they bumped up the date for 2011's FlashPaq to March/April, so that's good news!

 

513s rev my 35s to 2450 at 70 which IMO is a little high for the best milage at speed, I would like to see it around 2200 at 70..However, It didnt come all together UNTIL I added the superchip last. (now never have to turn OD off , jeep runs like stock under all conditions, this was not the case after just the gears)

If I had it to do it over I would be very intrested in the 488s and the SC. For the 33s the 488 will make it rev in OD too high.. again IMO.

I know exactly what your goin thru- Good luck.

 

Let's hope so I have a set of 285's that will be here at the end of march and I need that superchip flashpaq sine I'm not regearing. I too have an auto with 3.73 gears.

All though I question the stickied chart as I have 32" tires from the factory and 3.73 gears. The chard says this is minimal and little o.d. should be used. We use od any time it's on the highway and don't have performance issues. I have a hard time believing jeep would put in a gear set that wouldn't give the best gas mileage possible with the stock tires so they can claim as much MPG as possible.

 

Plug in your numbers in this calculator...

http://www.4lo.com/calc/geartire.htm

Not sure how to do the math to factor in auto vs. manual

 

You are the exception. Far too many of us feel that Chrysler dropped the ball on this one. Auto's are under-geared straight from the factory. (Or should have been given a different transmission.) For comparison, go look at those same charts, and plug the exact same gear/tire combo in for a Manual.

A question to ponder. Which will see the better mpg's?

2000rpm in OD, and constantly dropping out and going to 3000rpm OD Off.
2500rpm in OD, and maintaining OD.

A .69 OD is crap. With 'stock' gearing, we are dropping out of OD any time we hit an overpass, or try to pass anyone, or try to stay with the other traffic, or live at altitude, or in hilly country, or there is a crosswind, or heaven forbid, a headwind.

It may not have been obvious, but I agree with the chart.
And for those of you who can get away with sub-2k rpm's on the freeway, my hat is off to you. Wish I could manage it.

 

Sorry bud, that chart may work with some other vehicles, but doesn't work with JK's.

 

Don't get me wrong I think 4,10's should be an option on all of the jk's and I think the gearing could be improved for more power but I don't think a 3.73 is sub standard. Also living in CO you are a sub set of the nation, I know I lived there for about 6 years. Jeep needed to pick something that works for the majority of people not just for high altitude. The other reason I think this is they probably expected most of the automatics to be bought by mall crawlin soccer moms. And if they want to sell hard to that crowd they need to go with the best gas mileage possible with performance coming in second. Also note I'm used to driving a vehicle with 4.11's that at 70 mph I'm screaming along at almost 3400 rpm. This gives me some power but not the best mileage. It's always a trade off between the two. But I don't believe you need to jump from 3.73 to 5.13's for 1 inch of tire.And why would that posted site not apply to jk's? It is assuming nothing in your transmission is changing which is accurate.

While on first observation a car with lower rpm's should get better gas mileage that is only true if it is still in the power band. If at 2k rpm's you are out side of the power then no you will get worse gas mileage due to the fact that the car will use more gas trying to bring you into the power band, and the transmission will need to shift out of o.d., which most have to do to pass people or go up large hills any ways.

Now I'm not saying going up to 33's with an auto and 3.73 you wont notice a drop in power and mileage, you will. What I am saying is if you try it and don't like it try the superchips programmer first to try to change how the OD reacts.. There is a cost vs. benefit that needs to be looked at for an inch of tires.

I should state I am not just some bench racing junky I was a ASE master tech and have a degree in automotive technology(fancy phrasing for mechanic) so I do know a thing or two, and am just adding it in for conjunction.