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Unread 11-10-2007, 04:25 PM   #1
slater03
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Will switching from MTs to ATs gain back some gas mileage?

My gas mileage with my 33x12.50 kumho mts is about 12-13 mpg. The mts arent necessary for me since I barely go mudding anymore so I was thinking about swapping on some 32" or 33" ATs like BFGs or something. Would the ATs get me better gsa mileage?

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Unread 11-10-2007, 04:36 PM   #2
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I would say no unless you go smaller. I dont think tread pattern affects it near as much as tire size and gearing. Just keep your 33's and regear. If yoou have a 6 cylinder buy a set of 4 cylinder axles with 4.10 and if you have a four cylinder buy a set of 4.56 or 4.88's probably the same money to buy new tires or regear.
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Unread 11-10-2007, 04:48 PM   #3
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I really dont want to spend any money though and 4.10 axles would make it undriveable on the highway since with 3.55s now its about 3000rpms a 70
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Unread 11-10-2007, 05:46 PM   #4
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the mpg you MIGHT gain from the switch to at's will not be noticeable. tire wear, however, would be....

i would switch to an AT for THAT reason, but not for fuel economy....
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Unread 11-10-2007, 06:07 PM   #5
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I have a set of both. If I'm going to street it a lot I put on the AT's. Besides tread wear, I've noticed a 3mpg improvement. Not to mention better ride, handling, and noise level. The old YJ is almost civilized with the AT's on the street. I have to qualify that my AT's are 31x10.5
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Unread 11-11-2007, 06:55 AM   #6
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Quote:
Originally Posted by Big-n-Broke-YJ
the mpg you MIGHT gain from the switch to at's will not be noticeable. tire wear, however, would be....

i would switch to an AT for THAT reason, but not for fuel economy....
...Tire wear and ride quality would be the reason for the change. Increase in MPG would be so small you would not notice.

Todd
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Unread 11-11-2007, 07:01 AM   #7
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Quote:
Originally Posted by slater03
I really dont want to spend any money though and 4.10 axles would make it undriveable on the highway since with 3.55s now its about 3000rpms a 70
Not true. You would actually like it belive it or not. If your doing 70 alot, you want to be around 2300-2500 once your in that range.
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Unread 11-11-2007, 08:57 AM   #8
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Have you corrected your speedometer for the 33s or is your speedo still off?

If it is still off the 12 to 13mpg number is wrong and your milage is about 10% more making it 14mpg to 14.5mpg.

Does that sound better?
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Unread 11-11-2007, 09:03 AM   #9
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You've got the non-overdrive factory TF999 3-speed auto... they burn more gas than a stick. You have three choices really:
  • a) Replace the gears with 3.07s... that will lower your ratio and the RPMs all around, giving you less power but better mileage. Your freeway RPMs will be around 2200-2400 at freeway speeds
  • b) Lower your tire size to a 31" at most. That will accomplish the same thing as above
  • c) Get a tranny that has .75 overdrive like an AW4 from a Cherokee or a .7 overdrive 700R4. Both will give you a reduction in RPMs back to stock
The third option is the best but most expensive. The second is the least expensive but the one most people don't like due primarily to vanity". "Ewww... lower my junk, no way".
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Unread 11-11-2007, 12:25 PM   #10
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maybe completely irrelevent,but what kind tire pressure are you running. i know my mpg seemed to go a couple of more miles when i went back 32 psi on a/t's(probably my imagination). i was running 26-28 #'s before.just rides a little rougher and i can always take some out when needed.
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Unread 11-11-2007, 12:30 PM   #11
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When i had bfg a/t's they were louder then the trxus m/t's I have now. I really don't think that you will notice any difference in mpg's unless you regear.
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Unread 11-11-2007, 03:01 PM   #12
slater03
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Quote:
Originally Posted by jeeepguy
You've got the non-overdrive factory TF999 3-speed auto... they burn more gas than a stick. You have three choices really:
  • a) Replace the gears with 3.07s... that will lower your ratio and the RPMs all around, giving you less power but better mileage. Your freeway RPMs will be around 2200-2400 at freeway speeds
  • b) Lower your tire size to a 31" at most. That will accomplish the same thing as above
  • c) Get a tranny that has .75 overdrive like an AW4 from a Cherokee or a .7 overdrive 700R4. Both will give you a reduction in RPMs back to stock
The third option is the best but most expensive. The second is the least expensive but the one most people don't like due primarily to vanity". "Ewww... lower my junk, no way".
I was really considering swappint in a aw4 or atleast a lockup 32rh but I dont think the mileage gained back would make up for the iunitial investment. My whole goal is to save as much money as possible and I was hoping to find someone with ATs willing to trade for my MTs. And the noise and ride improvements would be welcome.
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Unread 11-11-2007, 03:26 PM   #13
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My AW4 swap cost me $600 total with all parts and materials. I went from 13-14 in the city to 16 or so and 15 on the highway to 18. I was driving about 160 miles a day back then and paid back the tranny cost in about three months. Its well worth it, even with lesser driving.
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"Great danger lies in the notion that we can reason with evil"
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Quote:
...We use words like honor, code, loyalty. We use these words as the backbone of a life spent defending something. ...I have neither the time nor the inclination to explain myself to a man who rises and sleeps under the blanket of the very freedom that I provide, then questions the manner in which I provide it. I would rather you just said thank you, and went on your way, Otherwise, I suggest you pick up a weapon, and stand a post...
Quote:
I bought the HI-WAY BLASTER HORN that's 139dB and every time I honk the horn an Angel dies.
Quote:
Revelation 13:16-18
16 - He causes all, both small and great, rich and poor, free and slave, to receive a mark on their right hand or on their foreheads,
17 - and that no one may buy or sell except one who has the mark or the name of the beast, or the number of his name.
18 - Here is wisdom. Let him who has understanding calculate the number of the beast, for it is the number of a man: (Real ID and RFID chips)
Think about it...
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Unread 11-12-2007, 09:36 AM   #14
coachchuck
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I disagree.
The milage difference for me is measurable, at about 2 mpg.

However there are a lot of variables that can change this.
My AT and MT are both 33s,
but the ATs don't weigh as much as the MTs.
I run about 28 psi in the ATs, the MTs at about 22 psi.
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Unread 11-12-2007, 12:45 PM   #15
slater03
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Quote:
Originally Posted by jeeepguy
My AW4 swap cost me $600 total with all parts and materials. I went from 13-14 in the city to 16 or so and 15 on the highway to 18. I was driving about 160 miles a day back then and paid back the tranny cost in about three months. Its well worth it, even with lesser driving.
I was claculating it up one day and I figured $300 for the cheapest tranny Ive seen, SYE (which I dont have now) $400, and new front driveshaft and I figured it would be close to $1000. I drive maybe 240 miles a week (roughly a week for very fill up) so it would take me forever to pay it off. I think Ill just search for some 32" ATs even if it wont save me much mileage.
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