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I'm getting conflicting advice on my gear ratio. Help!

Lucille73

New Member
Joined
Jan 4, 2012
Messages
14
Guys (and gals), I'm in a pinch. The restoration on my '73 beauty has been going great, but I've hit a bump. I'm building toward a highway daily driver, not a rock crawler. I'll go off-road occasionally, but this is definitely gonna be my daily ride. Living in Atlanta, fuel economy is very important to me.

The very smart mechanic helping on my build has coached me toward a 3.50 gear ratio, but the smart guys from one the major bronco suppliers say I should be at 4.56. These are very different perspectives, and I'm not sure where to go.

I have a '98 Explorer 5.0 302 and a late model 4R70W. My mechanic says the 3.50 ratio will give the best fuel economy and least amount of noise. The supplier says the 4.56 won't put me in the prime RPM range. My mechanic countered by saying the 4.56 will dramatically lower my MPG, and the 3.50 WILL keep me in the optimal RPM range.

I'm not qualified to diagnose this, but I gotta make a decision soon. Can any of you gear wizards shed some light on this so that I can have assurance in the right decision? I really appreciate the advice.
 

DirtDonk

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Nov 3, 2003
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47,353
Hey 73. What tire size are you going to be running? That's the remaining single most important part of the equation.

Opinions vary of course, because needs/desires/intended uses vary too.
Let us know tire size and what you intend to do when you do go off road (if you intend to at all that is?) and we'll give you more "opinions" to add to the list! ;)

Paul
 

DirtDonk

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It sounds like you might be thinking of larger tires, based on that 4.56 recommendation. The reason to use such a low gear, even on the street, is that based on your tires size, your engine might not even be able to pull freeway speeds in overdrive.
While the mechanic is correct in some ways, depending on the rpm range you end up in, if your tire size is larger than maybe a 31" tall tire, you run the risk of lugging even a good running EFI Explorer engine with too tall a tire.

Paul
 

Viperwolf1

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The 4R70W has a .7:1 overdrive ratio. Using that with a 3.50 gear is the same as using a 2.50 axle gear with a non-overdrive trans. It might be ok with 28" tires (think stock explorer) but won't work well with taller tires.
 

Mountain Ram

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4.56 would be good with 35s while 3.50 would be an issue with the same size tire. Weight of the tire is as significant as the size... Getting bigger/heavier tires moving with low numerical gears will suck the gas... As will keeping them moving on grades (inclines).

It may have been said ;D tire size is important here! ;D
 

DirtDonk

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Even Explorers were available with 3.73 and maybe even 4.11's during their production. And about the biggest tire you could get on them was a 30 or 31.
So even Ford didn't think that 3.50's were universally suited.

Paul
 

needabronco

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Jul 2, 2004
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6,411
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Prescott/Farmington
Worrying about fuel economy while discussing a Bronco build is quite comical! ;D Actually I run an AOD with 4.88's and 35"s, I average 14-16 on the highway with my 302. With a 4R70W and 3.50 gears you'd never even use overdrive with larger tires. At that point a stock C4 would be a much cheaper choice...

A 302 needs rpm's to be happy on the highway to stay in it's peak torque range. Think of your rig as a giant barn door being pushed through the road, this isn't an aerodynamic vehicle 'slicing' through the air...
 

Mountain Ram

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"Barn Door" truer words have never been spoken about the aerodynamic characteristics of our beloved chosen antiques!
 

DirtDonk

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With Fred Flintstone's feet dragging along underneath for good measure.
On fire too, of course. ;D

Paul
 
OP
OP
L

Lucille73

New Member
Joined
Jan 4, 2012
Messages
14
I'm debating between 33's and 35's

Funny, and all too accurate. It was late when I posted, so you're right, I forgot the most important part. I am debating between 33's and 35's. Does that change the argument and commentary?
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,835
All the above is true.
Tire size is the key factor we don't know.

4.56 gears won't do as much against the fuel economy as your mechanic thinks. My realtor was running an 5.0 Explorer and swapped the 3.55 gears to 4.30. Stock tire size and everything else. Had no noticable effect on fuel ecomony but it ran so much stronger on the street (and sometimes the drag strip).

Highway fuel economy you are fighting wind. When you look at a brick and realize that the brick is probably more aerodynamic then the Bronco. It isn't like pushing a new areo box down the road where you can idle. You need to keep the revs up a little bit so that you can make efficient power to fight the wind.

In short your mechanic is wrong, but without tire size we can't say how much.
 

Timmy390

Bronco Guru
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Jan 1, 2011
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5,609
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Conway, AR
I ran 32's with the factory 3.50's for the past 16 years I've owned my Bronco. I moved to 4.11's this summer and WOW what a difference.

Rear gears (depending on what brand you buy) are cheap enough (no need to go high dollar for testing) so why not get the ratio's you want/have been suggested and try them out? Run each set for a week noteing the pors and cons of each. Maybe you will get lucky and the last set you try is the ones you want to keep. You can then sell the ones you don't want on this board. Good gears sell quick.

Just don't lock the front in while testing......

Tim
 

Apogee

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Given your gear ratio and assuming a stock Explorer 5.0 cam, I would run 4.11 to 4.30's with 33's or 4.56 to 4.88's with 35's. For optimal fuel economy and performance, you want to be in the meat of your torque curve under the most common driving conditions. Having too low of gears (numerically high) will put you above that point in the RPM range and negatively impact fuel economy...having too high of gears (numerically low) will hurt performance and make it feel sluggish and unresponsive to throttle input at lower RPM's.

HTH,
Tobin
 
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