Help me understand what's going on with my MPG

[morejeepsthanicancount]

I just realized that I've never seen a Sport or Sport S dash before... I've only seen a Rubicon and Max Tow dash with the 8.4" system that has the full digital EVIC. I was like "WTF is up with his dash???" Then it hit me...

And yes, our Jeeps are SO aerodynamically inefficient that anything like that will affect fuel mileage, and usually for the better. I noticed an increase with my FF Stubby and Warn 9.5XP (steel cable) and 37's and lift up to around 13.5 (was at 12.5 stock), then up to 14.5-15 MPG after recalibration with the Tazer JL Mini and adding the iDrive unit. So I'm hoping that when I re-gear to 4.88's that it will go up to around 17+ average...But that will be down the road, unless someone offers me a hell of a price to do it.

I was perplexed as well. My Sport S has a full digital cluster with the 8.4. I never knew there was a different instrument cluster?!

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[noside85]

Clean look. I am looking at the same bumper...what winch is that?

Thanks. It's a Smittybilt 12k X2O, haven't really used it. Just only respooled every month or two, easy to use though.

 

[Jeepnoob34]

50 miles in on my way to Alabama. Relatively flat freeway. Average 16.4 and in 7th gear 98% of the time. It amazes me how much it switches or stays in 7th gear

 

[morejeepsthanicancount]

50 miles in on my way to Alabama. Relatively flat freeway. Average 16.4 and in 7th gear 98% of the time. It amazes me how much it switches or stays in 7th gear

What size tires and have you calibrated the ECU post tire size? My rig stays in 8th the entire time in the foothills of the mountains unless it's going up a hill. Thats will 33s, and going 68-72 mph. SC upstate is rolling hills and foothills of the blue ridge mountains.

 

[Jeeperjamie]

What size tires and have you calibrated the ECU post tire size? My rig stays in 8th the entire time in the foothills of the mountains unless it's going up a hill. Thats will 33s, and going 68-72 mph. SC upstate is rolling hills and foothills of the blue ridge mountains.

Same here on 35's in NC around the Charlotte NC area. Rolling hills, around 70-80 it stays in 8th gear unless I hit a decent incline.

 

[Jeepnoob34]

What size tires and have you calibrated the ECU post tire size? My rig stays in 8th the entire time in the foothills of the mountains unless it's going up a hill. Thats will 33s, and going 68-72 mph. SC upstate is rolling hills and foothills of the blue ridge mountains.

33’s. Nothing programmed. Didn’t think 1” was a big difference

 

[Jeeperjamie]

33’s. Nothing programmed. Didn’t think 1” was a big difference

Oh yeah, 1" is a difference. You can use this calculator to see how bad your speedo is off and that will definitely affect shift points. Your speedo is off by 3-4 MPH to the negative, which is going to affect your shift points for sure.

https://www.discounttire.com/learn/tire-size-calculator

 

[Jeepnoob34]

Oh yeah, 1" is a difference. You can use this calculator to see how bad your speedo is off and that will definitely affect shift points. Your speedo is off by 3-4 MPH to the negative, which is going to affect your shift points for sure.

https://www.discounttire.com/learn/tire-size-calculator

It’s definitely not off by that much. I’ve tested with laser and street radar up to 50 mph. It was within 1 mph every time. Maybe by the time I up to 75 it’s closer to the 3-4 mph you mentioned.

 

[Jeeperjamie]

It’s definitely not off by that much. I’ve tested with laser and street radar up to 50 mph. It was within 1 mph every time. Maybe by the time I up to 75 it’s closer to the 3-4 mph you mentioned.

At 50 it would be around 2.5 mph off. I'm just guessing you had 245 75-17 tires right off the lot and then installed 285 70-17 tires after, that's the most common 33 size I see people running. If your jeep is hanging on 7th then your shift points are definitely off and I would get a JScan and reset your computer, it's definitely off. I wouldn't put much faith on the radar signs on the road, they aren't that accurate either. Download a GPS app, or use Google maps, it will show you how fast your traveling and its pretty accurate. I'll be willing to bet if you reset the computer for your tires your shift points will go back to normal.

 

[Jeepnoob34]

At 50 it would be around 2.5 mph off. I'm just guessing you had 245 75-17 tires right off the lot and then installed 285 70-17 tires after, that's the most common 33 size I see people running. If your jeep is hanging on 7th then your shift points are definitely off and I would get a JScan and reset your computer, it's definitely off. I wouldn't put much faith on the radar signs on the road, they aren't that accurate either. Download a GPS app, or use Google maps, it will show you how fast your traveling and its pretty accurate. I'll be willing to bet if you reset the computer for your tires your shift points will go back to normal.

I have 275 70 18

 

[SwampNut]

Going from 33s to 35s made my shift points completely insane. So even 1" is sure to have an effect. Also, *actual* tire sizes vary a lot, even with similar size numbers. Putting different tires side by side, I've seen over a half inch difference.

 

[Jeepnoob34]

Guess I need to learn about this Flashing stuff

Going from 33s to 35s made my shift points completely insane. So even 1" is sure to have an effect. Also, *actual* tire sizes vary a lot, even with similar size numbers. Putting different tires side by side, I've seen over a half inch difference.

 

[Jeeperjamie]

I have 275 70 18

That's almost a 1-3/4" difference in height compared to stock tires. Your truck shift points and Speedo have to be off because that's a good difference it height. I just bought a BMW 440i that had 245 45 r18 tires on it and my speed was off on it pretty bad, by almost 5 mph. Went and had 225 45 r18 tires put on it and it's within 1 mph which I'm good with. JScan is only around $90, be worth giving it a shot to see if you can get them shift points back to stock and it's going to make your MPGs go up as well

 

[Jeepnoob34]

That's almost a 1-3/4" difference in height compared to stock tires. Your truck shift points and Speedo have to be off because that's a good difference it height. I just bought a BMW 440i that had 245 45 r18 tires on it and my speed was off on it pretty bad, by almost 5 mph. Went and had 225 45 r18 tires put on it and it's within 1 mph which I'm good with. JScan is only around $90, be worth giving it a shot to see if you can get them shift points back to stock and it's going to make your MPGs go up as well

Probably splitting hairs but I have been upgraded all-terrain tires that came on the Overland

 

[tstugel]

I'm right there with you on this. My bone stock JTR LE has never gotten over 15 MPG and is a dog pulling even an open trailer.

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