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Please explain like I am a 5 year old. New Tires, Gas Mileage drop.

lepcat

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I just moved from 2457517's on my 2018 Jeep JLU Sport S to 35125020(35x12.50r20) Yokohama X-AT's.(Love these tires BTW. Aggressive looking and damn near whisper quite) I have the 3.6. It still seems pretty peppy enough in daily driving. However it seems to be holding on to gearing longer when shifting. My gas mileage has also dropped by 2-3 MPH. I can understand that this might just be the world I live in now. I do have the tazer. Is there any adjustments I can do with it to help improve this? I see things like gear ratio adjustment in the tazer documents. And other options in Perf? setting that I should look at. I don't want to start messing around with those setting until I gain more knowledge. My assumption is those are to only be used if I have changed the physical gearing?

Overall... Any tips or tricks to improve this? Any other useful knowledge us newbies could gleam from the more senior Jeep owners out there?

Thanks for being an Awesome freaking community.
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Captain Obvious

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What is the new tire size? The format you used is hard to understand - it looks like you meant to say 315/25r20? This can't be right - at least I hope it's not! Maybe 315/50r20? That seems more likely.

OK, you've switched to a tire that is about 13% larger diameter. This extra diameter reduces the leverage that the engine can exert on the road surface in order to propel your Jeep. The wheels and tires are also heavier, which means more power is required to get them turning. Essentially, this change has made it more difficult for the engine to move the vehicle due to decreased mechanical advantage. This causes the computer to hold a gear for longer because it needs the extra power - just like if you were hauling a heavier load.

The Tazer cannot change your gear ratio, it can only adjust what your computer believes is the gear ratio. Changing the gears requires opening the axles and replacing the pinion and ring gear, and most likely the carrier in your axle as well.
 
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lepcat

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What is the new tire size? The format you used is hard to understand - it looks like you meant to say 315/25r20? This can't be right - at least I hope it's not! Maybe 315/50r20? That seems more likely.

OK, you've switched to a tire that is about 13% larger diameter. This extra diameter reduces the leverage that the engine can exert on the road surface in order to propel your Jeep. The wheels and tires are also heavier, which means more power is required to get them turning. Essentially, this change has made it more difficult for the engine to move the vehicle due to decreased mechanical advantage. This causes the computer to hold a gear for longer because it needs the extra power - just like if you were hauling a heavier load.

The Tazer cannot change your gear ratio, it can only adjust what your computer believes is the gear ratio. Changing the gears requires opening the axles and replacing the pinion and ring gear, and most likely the carrier in your axle as well.

Thanks for the reply. The tire size is 35x12.50r20 Yokohama GEO X-AT E Rated. Thanks for confirming my thoughts on the Tazer Gearing changes. The documents were fairly vague on that point. I do have the Fuel Vector D579 Rims at 20x9 with a 1 offset. And yes those are some heavy bitches when married to the tires. I absolutely love the look and more than willing to sacrifice some gas mileage for it. Plus I may look at physical re gearing in the future.
 

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Thanks for the reply. The tire size is 35x12.50r20 Yokohama GEO X-AT E Rated. Thanks for confirming my thoughts on the Tazer Gearing changes. The documents were fairly vague on that point. I do have the Fuel Vector D579 Rims at 20x9 with a 1 offset. And yes those are some heavy bitches when married to the tires. I absolutely love the look and more than willing to sacrifice some gas mileage for it. Plus I may look at physical re gearing in the future.
If you're looking at regearing, consider looking for a complete Rubicon axle setup from someone that upgrades them. You'll get stronger everything, 4.10 gears, and lockers in the deal, for not a whole lot more money, relatively speaking.
 

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lepcat

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If you're looking at regearing, consider looking for a complete Rubicon axle setup from someone that upgrades them. You'll get stronger everything, 4.10 gears, and lockers in the deal, for not a whole lot more money, relatively speaking.
I will keep an eye out for some. The eight speed tranny would have no issue with that?
 

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I will keep an eye out for some. The eight speed tranny would have no issue with that?
Can’t imagine why it would. There’s a couple people on this board that have done the swap, I’m sure there’s more info around here somewhere.
 

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Just to confirm, you readjusted for the new tire diameter with the tazer, right?
 

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I just moved from 2457517's on my 2018 Jeep JLU Sport S to 35125020(35x12.50r20) Yokohama X-AT's.(Love these tires BTW. Aggressive looking and damn near whisper quite) I have the 3.6. It still seems pretty peppy enough in daily driving. However it seems to be holding on to gearing longer when shifting. My gas mileage has also dropped by 2-3 MPH. I can understand that this might just be the world I live in now. I do have the tazer. Is there any adjustments I can do with it to help improve this? I see things like gear ratio adjustment in the tazer documents. And other options in Perf? setting that I should look at. I don't want to start messing around with those setting until I gain more knowledge. My assumption is those are to only be used if I have changed the physical gearing?

Overall... Any tips or tricks to improve this? Any other useful knowledge us newbies could gleam from the more senior Jeep owners out there?

Thanks for being an Awesome freaking community.
Have you used the tazer to adjust your speedometer to your new tire size?
 

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Yes I have.
Then you’re only option now is to re-gear, and you should way the cost difference of re-gearing, and axle swap, as others have suggested. If it’s within a few hundred bucks, I definitely would swap axles.
 

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Youre on a much heavier wheel/tire combo now and running tires that have more rolling resistance. The vehicle sits a little higher as well. All these combined contribute to poor mpg. My mpg tanked as well.
 

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Yes I have. Speedometer is spot on now.
Well, with that out of the way, it's simply the "new reality" of those heavier 20's and raller E rated tires working against the taller 3.45 gearing.

What matters most, is that it rides good and you're happy with it. Cheers!
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