To upgrade or not to upgrade, the question?

[DaddyO]

Sounds normal for that rack and RTT

I went from 4.46 to 5.38. My MPG went from 320 miles per tank to … 325 miles per tank

Do you run the same gear?

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[Brian_B]

Do you run the same gear?

same tires and transmission

 

[DaddyO]

If that’s the only similarity it doesn’t match as I run heavier weight than you do. In that case I’m afraid it doesn’t compare. What I’ve read is that due to the weight and larger tires that the upgrade would be beneficial for the Bronco and its longevity.

 

[Kevin Scarbel]

Confused to no end. Driving a 4-door ‘24 Badlands Sasquatch 2.7L with upgraded tires to 37’s, RC 2 1/2” lift with RC tie rod upgrade and track bar. Just received my Ford Procal to program the wheel sizes etc. I have a lot of gear and add ons including
Gobi roof rack
OpenRoad:
270 awning+sidewalls
12k hidden winch
Rooftop tent
Shower awning+water tank+water heater
Rhino:
Recovery boards
Tow ropes
Kinetic ropes
Soft shackles
Hard shackles
Tree savers
ARB onboard twin air pump
M2M tailgate table
Broaddict Molle panels
Pelican boxes
2 Jackery generators
Tools
And lots of stuff for traveling not listed.
I might add a cold air intake.

THE QUESTION: Should I upgrade my gears from 4.7 to 4.88s? Based on travel 65-70% highway and 30-35% offroad. I am getting mixed research recommendations. Currently getting 15-16mpg on longer highway trips of 300-600 miles. In town mileage is 12-13mpg. Did I miss anything?

If you're running 37" tires, of course you should have 4.88 gearing.

 

[Brian_B]

If you're running 37" tires, of course you should have 4.88 gearing.

Yeah…

but he’s already at 4.70

Thats what… a 4% change? For a couple thousand or more in parts and labor. You’d get much more out of just running one grade better gas

On the other hand - can ChatGPT ever really
be wrong?

 

[JL8jeff]

For the cost of that gear upgrade, you could do intake, charge pipes, intercooler, FPP or custom tune, cat-back exhaust and get better mpg. I did them all and went to 37's, 2" over Sas lift and even without the speedo correction I'm getting better mpg. I think I'm around .5 to .75 mpg better without correction so that would jump it another .6 or so. My overall avg is around 17.8 with no correction so it's probably a little better than that. Your weight is a big factor in hurting mpg but if you go over 70mph on the highway, that hurts even more. I'd save that gear change money for other mods that help performance.

 

[Felix808]

THE QUESTION: Should I upgrade my gears from 4.7 to 4.88s? Based on travel 65-70% highway and 30-35% offroad. I am getting mixed research recommendations. Currently getting 15-16mpg on longer highway trips of 300-600 miles. In town mileage is 12-13mpg. Did I miss anything?

Not a chance! Unless you are racing & looking to put the power at a specific part of a track, it is pointless to go less then 10% difference in gearing 15% you'll feel it 20% might be bit much for most.

The 4.7 gear set will be stronger and have more pinion engagement over the 4.88's. The only standard axle I know of that the R&P gets stronger is the 9"
(Edit below)
The 9" gains pinon engagement when going deeper lower Higher # gear sets because pinion placement & how it engages. Everything else standard loses pinion engagement the deeper the gear set higher #'s. You'll have more force on less surface area.

 

[87-Z28]

According to ChatGPT:

My Honest Recommendation For YOU

Because:

• You’re heavy
• You’re on 37s
• You drive 75 mph often
• You’re not going to 39s
• You’re not building a hardcore crawle

4.88 is the smarter choice.
It fixes the mechanical mismatch without overcorrectiing
If you were 50% off-road, I’d say 5.13.
But at 70–75% highway?
4.88 hits the sweet spot.


What 4.88 Will Do at 75–80 mph With your 2.7L:

Keep the engine in a better torque band
Reduce downshifts vs 4.70
Keep RPM moderate
Maintain good highway comfort
Improve off-road control noticeably
It will feel “corrected,” not aggressive.


What 5.13 Would Do at 75–80 mph
Strong off-road
Very responsive in town
Higher sustained RPM
Slight MPG drop vs 4.88
No real benefit unless you go heavier or larger tires

For someone cruising 65–70 mph? I’d lean 5.13.

For 80 mph? 4.88 is the better engineering balance.

Going from 4.70 to 4.88 is a 3.8% change.

 

[ThunderFlash]

Last trip from Austin south to Brownsville fighting a headwind it said I was getting 9mpg.

9 mpg is probably closer to 10 mpg corrected for the tire diameter and likely largely due to aerodynamic drag of the bluff body design of a Bronco + the butt load of aerodynamic drag due to all the crap strapped on the outside of it. Note that aerodynamic drag forces increase with the SQUARE of velocity, i.e. it increases RAPIDLY as speed increases. So if you were busting along at 70 mph indicated, it was probably closer to 75 MPH actual speed due to tire diameter/speedo error. Then driving into a 40 mph head wind, your effective relative airspeed would be 115 mph. That's hauling balls and a whole mega lotta drag force. It's faster than a Cessna 152 can fly. I believe 104 mph was do not exceed speed with the throttle to the fire wall. Burning fuel is how to over come that, and lots of it. I don't think gearing would have helped much.

 

[23OBX2.7]

weigh scaling it with driver and full load carfo and fuel would tell a story and help quatify benefit and what ration would deliver material benefit.

 

[DaddyO]

Gearing isn’t a MPG mod, it’s a mechanical optimization.
Where the Real Savings Come From (Often Ignored)

Transmission & Drivetrain Weat

With 4.70s + 37s + weight:
• More heat
• More torque converter slip
• More gear hunting
• More clutch cycling

4.88s reduce:
• Converter unlock events
• Shift frequency
• Throttle input needed to maintain speed

 

[87-Z28]

3.8%.

 

[Zakm]

The internet and forums are going to tell you to go up and 4.70s are not good enough but yet ford designed the raptor bronco to have 4.70s with 37s. Of course there will be benefits with going to a lower gear but there will also trade offs. If its worth it to you make the move otherwise I think you'll be good if you don't.

 

[DaddyO]

Do you run the same gear?

same tires and transmission

What I meant by gear is added weight. Steel fenders, steel under armor along with all the other items on my list. What is your broncos weight (GVWR?). As soon as the rest of my accessories are installed in a couple of weeks I’m heading to a scale and weigh. I am installing the ford procom tomorrow.

 

[Techun]

4% change in gearing is going to make zero difference on the highway. You may be in, say, 8th gear instead of 7th in some situation.

Bottom line if your vehicle takes (random guess) 65hp avg to maintain a certain speed, you're paying that MPG to go that speed.

Unless you have issues in first gear or 4lo, this is just you wanting to buy more toys.

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