Manual Transmission, 6th Gear Efficiency

ProdigyJKU

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Starting to think that 6th gear ratio might be impractical for tires over 32". I've noticed the when traveling over 70mph the 5th gear requires no boost, while 6th gear is regularly pulling 5-6psi. Fuel economy seems to be identical in both gears.

I know Ford originally had a ton of problems when they tried putting overly small ecoboost engines in larger vehicle, the 1.5L in the Fusion for example. The engines were undersized to the point where they were constantly running relatively high boost just to maintain cruising speed. All that constant boost caused a ton of extra heat and wear on components, hence all the turbo/engine failures and fires.

So I'm wondering if it would be in the best interest for drivetrain longevity to stay out of 6th when doing 70 or higher. I assume 70mph is roughly where aerodynamic drag overwelms the engines available N/A torque for that rpm range.

For reference I have a BD with 285/75R17 (34"×11.2") with a 4.46 diff ratio. I assume that SAS Broncos are roughly equivalent seeing as the 4.7 gearing basically compenstates for the 35s.

-End rant
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kodiakisland

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I never figured to get much use out of 6th gear. Seems way to high for an engine that wants to rev.
 
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ProdigyJKU

ProdigyJKU

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I never figured to get much use out of 6th gear. Seems way to high for an engine that wants to rev.
Just annoys me that it is essentially a useless gear.

In my JKU I would be in 6th gear from 30mph all the way to 80mph. And it wouldn't use boost unless going up an incline. The Jeep would also accelerate fine in 6th, with 4.10s and 33s.

Just wish they made 6ths gear slightly shorter. It's slightly irritating to have 6th and not use it. 😔
 

kodiakisland

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No big deal. If you don’t need it, don’t use it. I almost never use the top gears on my motorcycles. Gives you the ability to put some decent gears in the Bronco and still have a good top gear. Throw some 5.13s in there and you can use 6th all you want.

I would loved to have had a 4.88 option as I knew the gearing would be too high for my tastes. Kinda figured it would be a 5sp as configured until I eventually regear.
 
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HoosierDaddy

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Kinda figured it would be a 5sp as configured until I eventually regear.
LOL, 5 ... or is it 6?

side note: That crawler gear is actually a bit taller than I anticipated. Not really street useable, but it's no NP435! LOL
 

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What about down hill? About the longest stretch of highway mine will see is the Haleakala Highway its about 10 to 20 min max with about 2500 to 3000 ft elevation change. Just speculation that I will spend most of the way up in 4th gear. But on the way down its either nuetral and brakes or 6th gear to keep me from running out too much. In my CJ I used to run 5th downhill which I almost never used elsewhere. What goes up must come down right?
 

11Bronco1776

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I don't think it's that efficient but maybe squeeze out an extra mpg or two. Any sustained hwy driving I use it.

Gotta say, overall really loving the manual. Only day 5 with my Bronco so far.
 

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I drove a BL with only optional rims, not Squatch. The top gear seemed fine for highway speeds and relatively flat road with a few low hills. Like someone said, if you don't care for how it feels, just regear the differentials. I thought it drove well but folks like what they like.
 

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What about down hill? About the longest stretch of highway mine will see is the Haleakala Highway its about 10 to 20 min max with about 2500 to 3000 ft elevation change. Just speculation that I will spend most of the way up in 4th gear. But on the way down its either nuetral and brakes or 6th gear to keep me from running out too much. In my CJ I used to run 5th downhill which I almost never used elsewhere. What goes up must come down right?
I don't think many people would recommend operating in neutral for any length of time.
 

kodiakisland

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LOL, 5 ... or is it 6?

side note: That crawler gear is actually a bit taller than I anticipated. Not really street useable, but it's no NP435! LOL

5 usable for me anyway(yeah, maybe 6 with crawler), but I don't do a lot of interstate driving. I'm OK with not using all the gears.

Part of the problem is he went from 32 inch tires to 34. Diff gears matter. As I said before, I wish I could have ordered lower gears on my BD as I will be running into the same issue. I would have gladly paid extra for factory 4.88s.

In the end I don't care. I let the engine tell me what gear it wants to be in and go with that.
 

Dads_bronze_bronco

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Starting to think that 6th gear ratio might be impractical for tires over 32". I've noticed the when traveling over 70mph the 5th gear requires no boost, while 6th gear is regularly pulling 5-6psi. Fuel economy seems to be identical in both gears.

I know Ford originally had a ton of problems when they tried putting overly small ecoboost engines in larger vehicle, the 1.5L in the Fusion for example. The engines were undersized to the point where they were constantly running relatively high boost just to maintain cruising speed. All that constant boost caused a ton of extra heat and wear on components, hence all the turbo/engine failures and fires.

So I'm wondering if it would be in the best interest for drivetrain longevity to stay out of 6th when doing 70 or higher. I assume 70mph is roughly where aerodynamic drag overwelms the engines available N/A torque for that rpm range.

For reference I have a BD with 285/75R17 (34"×11.2") with a 4.46 diff ratio. I assume that SAS Broncos are roughly equivalent seeing as the 4.7 gearing basically compenstates for the 35s.

-End rant
Don’t know / time will tell, but my JK on 33’s with gearing for 32’s spends most it’s time in 5th gear—6th for downhill or wind behind you above 60mph for 160000 miles—and has been fine.

Did not notice this (pay attention to boost) on the Badlands I drove though.
 

kodiakisland

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Don’t know / time will tell, but my JK on 33’s with gearing for 32’s spends most it’s time in 5th gear—6th for downhill or wind behind you above 60mph for 160000 miles—and has been fine.

Did not notice this (pay attention to boost) on the Badlands I drove though.

The stock badlands is geared a lot better though for actually using that 6th gear. It has 33 inch tires with 4.70s verses his BD running 34s with 4.46s. Not a huge difference, but the edge definitely goes to the stock BL.
 

HoosierDaddy

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5 usable for me anyway(yeah, maybe 6 with crawler), but I don't do a lot of interstate driving. I'm OK with not using all the gears.

Part of the problem is he went from 32 inch tires to 34. Diff gears matter. As I said before, I wish I could have ordered lower gears on my BD as I will be running into the same issue. I would have gladly paid extra for factory 4.88s.

In the end I don't care. I let the engine tell me what gear it wants to be in and go with that.
So, I put like 90 miles on my 2.3/7spd Base 4.46 on 30's, last night. Nothing really above 60 maybe 65, but I can tell you, 6th gear flattens that motor out.
Flat land, it would still accelerate a little
 
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