3.73, 4.27 & 4.46 ratio on-road?

[MacHudson]

Realistically speaking, the fastest I ever get to on the highway is about 80 mph. I cruise in the 70s. I’m simply not the kind to to 100 mph, which is basically impossible where I live.

I live where stop and go traffic is a fact of life. More giddy up from the light would be welcome

So, would a shorter gear reasonably cause me any trouble? What kind of “maximum top speed” are you talking about with a low gear on the automatic 10 speed?

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[Tdifonzo]

Realistically speaking, the fastest I ever get to on the highway is about 80 mph. I cruise in the 70s. I’m simply not the kind to to 100 mph, which is basically impossible where I live.

I live where stop and go traffic is a fact of life. More giddy up from the light would be welcome

So, would a shorter gear reasonably cause me any trouble? What kind of “maximum top speed” are you talking about with a low gear on the automatic 10 speed?

Download the Excel doc in this thread. Highway cruising RPM doesn't change too much no matter which tire size, gear ratio combo you go with.

Gear Ratio Speed Calculator

 

[The Pope]

So for my setup, from what I understand so far, get a Badlands on 33 with the 4.7 since I plan to do 35s on my own, and I should be good switching between sizes 33 and 35 regularly, and shouldn't have an issue cruising 90mph on the freeway. Correct?

You "should" be fine. Just make sure that you re-calibrate your speed odometer when you switch tire sizes.

 

[PRA4SNW]

So, with my planned configuration - Big Bend, 2.3 Auto, stock wheels and tires with no plan on upgrading soon, mostly highway driving - I would be okay with either gear, really, and not notice too much of a difference, with the 10 speed auto..
But, if I ever wanted to upgrade to a bigger tire, or do some trailering, or trail crawling, the 4.27 gear would best.
Probably best to buy the upgrade now. Plus, the locker rear would be nice to get unstuck from any winter jam-ups that can happen here in NH.
Thanks for all of the advice.

 

[lsustang05]

So for my setup, from what I understand so far, get a Badlands on 33 with the 4.7 since I plan to do 35s on my own, and I should be good switching between sizes 33 and 35 regularly, and shouldn't have an issue cruising 90mph on the freeway. Correct?

Other than it being a brick and you’ll feel every cross-breeze at 90mph, no. The gears won’t be an issue.

 

[Economisto]

Other than it being a brick and you’ll feel every cross-breeze at 90mph, no. The gears won’t be an issue.

Awesome, thanks! Its not my daily and i dont cruise at 90, but i want to be sure it can handle it when i do need to pick up some speed. Always have extra headroom!

 

[LarryZiegler]

Calculator I found has the gear ratios similar to 5th for the manual and 9th for the automatic transmission.

All speeds kept similar at 70mph.

Feel free to dive deep, and let us know what you find.
https://spicerparts.com/calculators/engine-rpm-calculator

4.46-33s and 4.7-35s is closer to normal for me in RPM and driving conditions at 70mph.

I like this calculator, but the variable it doesn’t show is the Overdrive gear ratio, which on the Bronco is .636. To get truer numbers on the right side of the calculator, you need to multiply the axle ratio times .636 to get a final drive ratio. The Overdrive field on the right side does not specify what that gear ratio might be and one must assume the ratio in D mode or 3rd gear mode is 1:1. It also appears that the Automatic field shows torque converter slippage that slightly raises RPMs. But don’t lock up torque converters cure that issue?

 

[Hoofnmouth]

My girls 2019 jl wrangler sport has the 3.6 v6 and 3.45 gears and an auto trans. With 35s it feels like direct drive it has lots of pep right off the bat. 3.45s seem kinda tall to me but i guess it works well with the gearing in the transmission. I wouldnt change a thing.

 

[Raptor911]

FYI ... the raptor runs 35s and runs a 4.1 rear. Why does it not run a 4.7 or even 5s?

Technically, 5.38-5.68 would be best for the high revving Ford engines and 35-37" tires.

Too bad the only axles that will take gears that deep and live a long life are, ironically, the classic Ford 9" axles.
You're looking at +$10,000 swap to do that.


The Bronco's OD gears are deep enough and the engines are powerful enough in very high RPMs, to get away with using OD to drive and direct (7M) 1st OD(10A) pass.

Older Brand X vehicles have either low RPM big block power that needs shallow gears for highway cruising. Or deep OD gears in a weak engine.

The Bronco is the first to have the best of both in one package.
Hopefully, the aftermarket will pick up and a 9" swap will get cheaper.

 

[Incognito]

FYI ... the raptor runs 35s and runs a 4.1 rear. Why does it not run a 4.7 or even 5s?

Yup.
Some even run 35"s with 3.73.

The question is not if it will move, it's a matter of moving most efficiently.

Deeper gears are better for crawling.

The Raptor and the Jeep Rubicon make due with 4.10s because of federal CAFE MPG #s.
They are less effective from a standing start and lose some slow speed performance, but get better highway cruising results that the Federal overlords demand.

 

[tokyo]

Best point made in this thread is that the "perfect" gear combo completely depends on your usage and no matter what you choose the spread of gears across the A10 tranny will probably work fine.

As another data point My F-150 4X2 weighs similar to a 2-door Bronco. It has 2.7 with A10 3.73 gears and 33's. At 80mph it is loafing along easily in 10th gear at ~2k rpm. Perfect and relaxed for me as I tend to spend a good amount of time at 80mph+ lots of wide open flat out here. I average ~20mpg mixed.

With T/C off and locker engaged it will still light up both rears from a standstill and is very fun to drive around town. Of course with 4.10 or lower gears it would spin the tires even easier but the trade off would be higher RPM on the 80+mph cruising. for ME this current combo is perfect.

But I am sure whatever combo I decide to buy will be fine too.. the spread in RPM at 80MPH isn't much:

3.73 with 30"s 2,191
4.27 with 32"s 2,352
4.7 with 35"s 2,367
3.73 with 32"s 2,054
4.7 with 33"s 2,510
4.46 with 33"s 2,382
4.46 with 35"s 2,246

 

[Used2jeep]

[/QUOTE]

So, 4.27 is slower than 3.73?
I'm new to all of this.

Well to answer that, you've got to know which engine & transmission your getting and where the "Sweet Spot" (RPM) the engine likes to operate at.

2.3 and 2.7 stock power bands for reference:

 

[PSUTE]

Best point made in this thread is that the "perfect" gear combo completely depends on your usage and no matter what you choose the spread of gears across the A10 tranny will probably work fine.

As another data point My F-150 4X2 weighs similar to a 2-door Bronco. It has 2.7 with A10 3.73 gears and 33's. At 80mph it is loafing along easily in 10th gear at ~2k rpm. Perfect and relaxed for me as I tend to spend a good amount of time at 80mph+ lots of wide open flat out here. I average ~20mpg mixed.

With T/C off and locker engaged it will still light up both rears from a standstill and is very fun to drive around town. Of course with 4.10 or lower gears it would spin the tires even easier but the trade off would be higher RPM on the 80+mph cruising. for ME this current combo is perfect.

But I am sure whatever combo I decide to buy will be fine too.. the spread in RPM at 80MPH isn't much:

3.73 with 30"s 2,191
4.27 with 32"s 2,352
4.7 with 35"s 2,367
3.73 with 32"s 2,054
4.7 with 33"s 2,510
4.46 with 33"s 2,382
4.46 with 35"s 2,246

Thanks for the real life info!

 

[LarryZiegler]

I will be running 32 in tires on mine and I'd rather have too low a gear (higher numerically) than too high of a gear. The 10 sp auto overdrive gearing of .636 brings the final gearing down below 3.00 for cruising speed purposes. I dealt with that with my 1970 Bronco w/3.50 rear end, 1:1 3rd gear ratio and stock 28 in tires. When I went to 30-31 in tires, the performance and gas mileage really suffered moreso to the fact I had a 120hp 302 in it....just no power to pull that high of a gear with the larger tires. With the 2.7, power won't be a problem, but I'm willing to sacrifice gas mileage for better lower end power, thus I will be opting for 4.27 gears instead of the standard 3.73.

 

[Yota85]

There's a bit more to it than 4.xx gears turns 2100 rpms at 65 mph vs ...... 4.88 etc....
Think of riding a 10 (or 12) speed bike.
Put the front derailer in the "high" sprocket (the big one)
Put the back derailer in the "high" sprocket (the smallest one)
Pedal around slowly for a bit, then try to accelerate quickly or to go up a hill.
It's hard on your legs, and you wish you prob wish you had the legs of a bicycle athlete.
The same is true with "tall" axle gears, like 3.07, 3.27. It's nice and comfortable to pedal when the going is easy, but when it get's tough it required much more effort on your part.
You wish you could change gears. (downshift), but YOU CAN'T. (the rear derailer represents your rear axle ratio)
So, you have to downshift the front derailer (represents your transmission in a truck. 2 speeds, but you get the idea, unless you're doing this on a mtn bike where you'd have 3 front gears)
This would represent very "tall" gears in an axle, like 3.07.

Now try the same experiment with the rear derailer in the low gear (biggest sprocket), and front also in high gear (biggest sprocket)
Easier to climb hills and accelerate with much less effort and little need to downshift your front derailer (transmission). But, you need to pedal like hell to go fast.
This would represent a "shorter" gear ratio, like a 5.29

Same idea with a truck. Though it's more complicated because of engine power/torque curves and all, but that's the basics.
Your engine will not work as hard with shorter gears. Climbing, towing, rolling 35" tires, or just maintaining 75 mph on the highway. BUT don't expect to do 110 mph. (I guess you shouldn't expect to do that in a Bronco anyways)

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