Shifting question

[Crj30047]

Good evening everyone, I have a 2022 gladiator on 40x13.50x17s..I purchased the vehicle this way with about 8k miles on it…after purchasing the vehicle I noticed the speedometer was WAY off so I took it back to the dealer to have it recalibrated..my issue now is that the vehicle NEVER goes past 5th gear on its own and holds 4th for a very long time. At highway speeds 75-80 mph I’m in 5th banging along 3500 4k rpm..MPG at a steady 14.2.. what’s needed to be done to correct the shifting issue? I hear others with the same issues and say that it’s a programming problem. Thanks in advance!

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[Gvsukids]

Good evening everyone, I have a 2022 gladiator on 40x13.50x17s..I purchased the vehicle this way with about 8k miles on it…after purchasing the vehicle I noticed the speedometer was WAY off so I took it back to the dealer to have it recalibrated..my issue now is that the vehicle NEVER goes past 5th gear on its own and holds 4th for a very long time. At highway speeds 75-80 mph I’m in 5th banging along 3500 4k rpm..MPG at a steady 14.2.. what’s needed to be done to correct the shifting issue? I hear others with the same issues and say that it’s a programming problem. Thanks in advance!

Gearing plays a part too. Seeing that you are lifted, you have a very large frontal area.

 

[Crj30047]

I figured gearing would play a vital part in the issue,but I’ve seen others with Similar setups and they’ve not regeared and are saying that they notice a little lag and a lot of downshifting but not as bad as what I’m describing..Florida is mostly flat and I figured at highway speeds it would atleast shift to lower the rpm but it doesn’t unless I do it manually

 

[Nance146]

What gvsukids said above. You’re sitting tall with a large area and heavy tires. Not sure what your exact setup is but I dropped some info into grimmjeepers website to approximate what you’re seeing. I’m estimating that you’re still rocking 4.1 gears with 40s which is suboptimal. Try browsing the forums a little and see what gears people recommend for tires that large or play around with the gearing grimmjeepers website and see what gearing brings your 8th gear rpm up.

I know very little about 40s except that they are massive so maybe others with experience will chime in.

 

[ShadowsPapa]

Good evening everyone, I have a 2022 gladiator on 40x13.50x17s..I purchased the vehicle this way with about 8k miles on it…after purchasing the vehicle I noticed the speedometer was WAY off so I took it back to the dealer to have it recalibrated..my issue now is that the vehicle NEVER goes past 5th gear on its own and holds 4th for a very long time. At highway speeds 75-80 mph I’m in 5th banging along 3500 4k rpm..MPG at a steady 14.2.. what’s needed to be done to correct the shifting issue? I hear others with the same issues and say that it’s a programming problem. Thanks in advance!

Did you mention the gears in that thing? What ratio are you running?

My Overland, 3.73 differential ratio, and stock diameter tires, doesn't often see 8th gear in our hills and wind. On a typical windy day, I can drive 30 miles on I80/35 at 70 and only ever see 6th gear.
When I take what we call "the bypass" up to town (Altoona) there's a fair incline for a couple of miles and I see 5th as it accelerates up to 70 as well as it can. Then it finally moves up, but all the way to town I don't see 8th gear.
Any wind has an impact even on mine - yours will be a LOT worse because now you have the rough under-belly exposed to the air, causing more drag. Wheel openings are scoops, the underside catches air and causes drag, the frontage of those huge tires is a big drag. Tires matter -the more tire that faces the wind, the harder it struggles.
You need deep gears for those tires, IMO.
Maybe you've noticed how vehicles for the highway - trying to get mpg - have 0 tire exposure. The fronts are simply never shown to the wind.

I’m estimating that you’re still rocking 4.1 gears with 40s which is suboptimal.

Understatement.

 

[Reddog]

What ShadowsPapa said is spot on. I had a JK with LS conversion and 6L80 trans previously and did a lot of testing (retired Civil/Structural Engineer) to see how to get better airflow thru the grille. Airflow as it affects the front of a Jeep is important. Basically, a stock Jeep is about as aerodynamic as a shipping crate and then most of us make it even worse by adding big tires and a lift and then wonder what happened to the fuel mileage and performance. As the speed of the vehicle increases, weird things begin to happen with the frontal air flow. At about 60 mph, the air flow piles up and becomes so turbulent at the front of a Jeep part of it actually reverses direction. No kidding. So, when you put very large tires on an already airflow challenged vehicle and then lift it higher in the air, it has a significant effect on the efficiency of the vehicle systems as it goes down the road. If I were putting 40's on my Gladiator, I would go to 5:12 gears I think. Bottomline, never underestimate how much airflow affects you Jeeps performance. I apologize for rambling here but was just trying to illustrate a point about airflow.

 

[Crj30047]

Well I reckon a re gear is the only way to fix it..5:12s I guess

 

[ShadowsPapa]

What ShadowsPapa said is spot on. I had a JK with LS conversion and 6L80 trans previously and did a lot of testing (retired Civil/Structural Engineer) to see how to get better airflow thru the grille. Airflow as it affects the front of a Jeep is important. Basically, a stock Jeep is about as aerodynamic as a shipping crate and then most of us make it even worse by adding big tires and a lift and then wonder what happened to the fuel mileage and performance. As the speed of the vehicle increases, weird things begin to happen with the frontal air flow. At about 60 mph, the air flow piles up and becomes so turbulent at the front of a Jeep part of it actually reverses direction. No kidding. So, when you put very large tires on an already airflow challenged vehicle and then lift it higher in the air, it has a significant effect on the efficiency of the vehicle systems as it goes down the road. If I were putting 40's on my Gladiator, I would go to 5:12 gears I think. Bottomline, never underestimate how much airflow affects you Jeeps performance. I apologize for rambling here but was just trying to illustrate a point about airflow.

The point of reversed air was illustrated quite nicely to me last winter when my HVAC was acting up and the temperature display said it was 101 degrees when it was about 15 outside with snow on the ground.
With the snow plow on the front, the air was being sucked FORWARD out of the engine bay, heating the temperature sensor just back of the grill, and causing the HVAC to believe I needed AC, and shut down the heat. We were freezing in that truck.
Weird things can happen.
OTR trucks have air dams to prevent wind from hitting the tires, and they even run pieces in the wheel to make the wheel not a dish, but a smoother surface for air to go past.
If the MPG is low, it means drag is high and the engine has to work harder to overcome it, preventing up-shifting.

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