Jeep Wrangler Forum

Jeep Wrangler Forum (http://www.wranglerforum.com/)
-   TJ Tech Forum (http://www.wranglerforum.com/f210/)
-   -   Gears (http://www.wranglerforum.com/f210/gears-4668.html)

Serg 12-22-2006 10:52 AM

Gears
 
I have a stock 02 Wrangler Sport with a 4" lift and 33" tires. Now that fuel is increasingly more expensive I don't drive my toy as often as I like. I'm considering changeing the gears and needed some suggestions. First, I do not know what gears I currently have now. Second, what should I replace them with to improve fuel efficiency?

Serg

MouthfulOfGrass 12-22-2006 05:18 PM

What kind of fuel efficiency (gas mileage) are you getting now ?

4Jeepn 12-22-2006 09:45 PM

Put smalller tires back on. Or go buy a beater for 2k and drive it for mpg increase,, much cheaper....

Mudweiser 12-23-2006 08:48 AM

Well if you got the 6 cyl, depends on whether you have an auto or 5 speed. With an auto you prolly have 3:07 or so, and with a 5 speed 3:73. With the 5 speed i wouldnt worry bout gear changing unless you just want to go 4:11 but its a small change. 4:56 are doable but thas way low geared. With the auto you could change to 3:73 or 4:11. But if you got the 4 cyl double everything i just said. 4:56 to 4:88s for the 4cyl. Its just a matter of opinion and what you need out of the jeep. Trail ready = bad gas mileage.

Siggie 12-23-2006 01:08 PM

Yeah, I agree. In my humble opinion, the four factors that influence fuel economy are:

Vehicle weight
Gearing
Engine displacement
Aerodynamics

This ignores driver behavior. I changed the drive ratio in my 1970 Mustang from 3:00 to 3:50 and noted two things. I raised the engine RPM and sucked gas like a B#$stard.

It's funny because I'm a Jeep owner newbie and after driving my 04 TJ (5sp, 6 cyl) I couldn't help but think -- 1st gear is geared so low, it's almost useless. For folks that don't off road regularly (I've never, but am considering going this year) why the hell doesn't Jeep offer a "road gear" option?

I'm sure that's a stupid question. But if they did, I'd bet gas milage for the platform would be raised significantly. At 70MPH with stock road tires, my six is turning 2700 RPM. And in all of the lower gears, the driveline ratio is so high my tach looks like a windshield wiper turned to "driving rain" as I shift from 1st to 4th.

Anyway, I asked about parts cost to change out the final drive to a 3:07 -- the response was "thousands of dollars." The way I analyzed that is this:

If I spend $2000 to give my beloved Jeep longer legs (each engine crankshaft revolution propels the Jeep further on down the road) I might improve the overall fuel economy -- what -- 10%? Let's guess 20% as an optimistic (and probably unreasonably optimistic) estimate. Well, my TJ gets 15miles per gallon. So by my screwed up math, the $2000 gets me an additional 3MPG. If I drive 10,000 miles per year, at 15MPG, I would normally burn 667 gallons - $1667 at the lowest California gas price of $2.50/gallon)

Well, if I spent the money to improve gas milage, the math shows that with the 3MPG improvement (to 18 MPG) reduces my yearly fuel use to 556 galloms ($1390 annual fuel cost). The difference is $277 per year. Yikes! I'd have to drive the car 7.2 years just to break even on the $2000 investment! :eek:

And of course, it will cost more than $2000 and the fuel economy improvement will certainly be less than 20%. Not to mention the affect on warranty, loss of off roading capability and the fact that there's serious work to change out the gear.

Personally, i think we're headed toward a permenant $4-6 per gallon fuel price, so as that occurs, I may reconsider. (Or go get a Porsche 914 for $3000 as a daily commuter :D )

Anyway, belive you me, lots of us have had the same thought about improving gas milage for Wranglers. Ultimately, the deal is this: No car does it all. The Wrangler, in my book, comes the closest, and it's a beautiful automobile. Focus on it's good points -- a fun, rugged, non pretentious piece of American automotive excellence that matches Siggie's personality. :D

Gas milage be damned!

Jerry Bransford 12-23-2006 01:56 PM

Yep, as Siggie so well put it, it's just not worth the expense of regearing in an attempt to improve your TJ's fuel mpg rating a tad. It'd take too many years to recoup the costs. Now if you regear for the reason of restoring the power and improving your Jeep's offroad ability lost due to the power loss caused by your 33" tires, then everything combined makes regearing worth the $$$. It may even slightly improve your MPG but don't regear solely for that reason as it won't improve it much... if it's even noticeable.

For 33" tires and a 5 speed manual transmission, 4.56 is an ideal ratio. If you're running the 3-speed automatic, 4.10 is a great ratio. :)

Serg 12-23-2006 04:32 PM

I do have a 5 speed manual. Never did the math, thanks for the education... Now that I know this I will reconsider. It is my toy for the weekends and to the beach adn by no means a daily commuter.

hazmat 12-23-2006 07:25 PM

jerry would 4.56 w/ the 6 spd be optimal as well ?

Jerry Bransford 12-23-2006 10:01 PM

Quote:

Originally Posted by hazmat (Post 40359)
jerry would 4.56 w/ the 6 spd be optimal as well ?

Yes indeed, at least for 33" tires it would be. :)

hazmat 12-24-2006 01:31 PM

thanks !


All times are GMT -5. The time now is 08:01 PM.