Street Rig Only 4R70W Explorer 5.0L 33x10.5's gear ratio results from GrimmJeeper

[Broncobowsher]

Another data point...
Friend of mine had a 5.0 Explorer as a daily driver. Realtor. Lots of driving all over town. Originally came with 3.73 gears with the tow package. He swapped them out for 4.30 gears and loved it. No loss in economy in daily driving. When he towed his race car, it towed better. Quicker ETs at the drag strip. Only down side was the ECM wasn't as happy and would short shift at the drag strip. This was also the very early days of anyone doing any tuning on these ECMs as well. And that was all with stock tires. 29" or so.

 

[Yeller]

I don’t feel 4.10 is worth the swap from 3.73, I would gladly do 4.30, which is what the numbers really call for, but unless it gets an SAS that isn’t happening, not available for the IFS D35, so it would have to be 4.56.

As a derailing and possibly interesting side note for bronco geeks doing math

Most broncos with a 302 came with 3.50 gears. The stock tire size was G78-15 which is equal to a 205/75-15 or 215/75-15, depending on which chart you look at. Those are 27.1” and 27.7” tall. A common error assumed is that the stock size in modern size is 235/75-15 which is 28.9” tall. The beloved 5.0 explorer and 4R70 transmission almost all had 3.73 gears, there were a few exceptions, but very few. They verifiably came with 235/75-15. Statistically the in the 2 vehicles the 3.50 gear in the bronco and the 3.73 gear in the ex are the same given the tire diameter difference. So…. What does that mean? IMO Watching the what the OEM’s do, there really is no huge reason to ever make a gear swap until you reach a 10% window of change. So to arbitrarily change from 3.73 to 4.10 doesn’t make a lot of sense for a 33” tire. Whereas going from 3.50 to 4.10 does going to a 33” tire. Mathematically a 4R70 with 33’s 4.30 is the ideal swap. Gives a tiny bit of increase to deal with a heavier tire and wheel. 4.56 gears will give a little more grins out of the hole, but not enough to really make a big difference being a 6% change, exactly like splitting hairs between 3.50 and 3.73, or a 215/75-15 and a 235/75-15 tire, it is virtually imperceptible. There is the placebo effect that can be massive but in reality it is statistically irrelevant unless you racing and digging for every advantage for a particular track. Last I checked, only a very small handful are going that. Synopsis, anything within 8% is close enough for 99% of us and will never notice the difference except in out own minds.

 

[skrit]

@Yeller
This is exactly my rationale for choosing the 4.30. I guess I'll walk back my need for head snapping performance in lieu of a more balanced gear ratio.
@Broncobowsher
Yes, plan is to only do the rear first. Axle rebuilds and re-gears are expensive - especially adding a Trutrack and I'm not going to even attempt to DIY this. I'm assuming that If I keep it in RWD (via twinstick) and not engage the front drive shaft then I should have no issues testing with the existing D44 3.50 gears.

All others - thanks for your advice, experience and wisdom.

 

[Yeller]

Yes as long as you don’t engage 4x4 you won’t have any issues.

Even then you would have to shift to 4x4 and lock the hubs at the front wheels, if you don’t do both you’re still not connecting the front tires to the drive train to be driven. Something often overlooked with today’s “everything automatic” vehicles. Many times I’ve come up on people “stuck” on a trail and discover 2 things. 1 - they don’t have the hubs locked. 2 - they are in high range. Show them how to change those 2 newby errors and they drive away on their own. The most recent times have been on back roads in National Parks.

 

[bigmuddy]

I once blew out my rear driveshaft going to see my girl in college. The CV had finally let go and I sat there wondering what the hell to do, I then realized if I take it off I can still get there in front wheel drive.

I know most of us know this but at the time it hadnt really occured to me. Drove it around like that until I could afford to get a new shaft, man I was broke back then...

 

[EFI Guy]

4.30 would give you just a little less gear than the Explorers factory ratio and tire size works out to be. It isn't terrible but you're going to be turning much heavier tires. 4.56 would give you just a tad more than the factory Explorer. I personally would consider 4.56 the minimum that I would run with 33s and wouldn't hesitate to up it to 4.88 for a little performance.

Don't fear the gear!

 

[DirtDonk]

I agree with all the logic posted so far.
But have you considered just putting it together and driving it with the existing gears? You already own them, they’re already set up, you can drive them and see just exactly if it’s a dog, or not.
That might help you, better than any chart, to decide between the 4.11, or the 4.30, or the 4.56 choice.

 

[pb4957]

I have a 302 (heads and cam have hp up a good bit) and am looking to run 33's. I want the same kinda performance as the original poster. A street/highway ride that keeps up with traffic. I was thinking 4.56 gears with an OD transmission. 33's seem to make highway speed much easier.

 

[skrit]

I agree with all the logic posted so far.
But have you considered just putting it together and driving it with the existing gears? You already own them, they’re already set up, you can drive them and see just exactly if it’s a dog, or not.
That might help you, better than any chart, to decide between the 4.11, or the 4.30, or the 4.56 choice.

Here is the issue with testing things out "as is" - there is no assembled as-is

 

[DirtDonk]

That’s as much a runner as many!
So are you saying you don’t even have front or differentials at this point? So nothing set up that you can bolt in, means you do have to choose your gears ahead of time.
Unless you can find a couple of donors or cheap takeoffs that you can slap in temporarily.

 

[skrit]

That’s as much a runner as many!
So are you saying you don’t even have front or differentials at this point? So nothing set up that you can bolt in, means you do have to choose your gears ahead of time.
Unless you can find a couple of donors or cheap takeoffs that you can slap in temporarily.

exactly - I only want to do this once!

 

[Tricky Dick]

exactly - I only want to do this once!

I would say err on the high side (numerically) then. I don't think you'll be disappointed with 4.56 and if you ever decide to bump to 35s it will still be a nice match.

 

[skrit]

I would say err on the high side (numerically) then. I don't think you'll be disappointed with 4.56 and if you ever decide to bump to 35s it will still be a nice match.

I'm starting to lean that way @Tricky Dick since it's been suggested several times on this thread and several others....still have plenty of time to decide but that's my next big expense so I'm doing as much reading I can of others experiences. Even over at the explorer forum: https://www.explorerforum.com/forums/.

 

[skrit]

4.30 would give you just a little less gear than the Explorers factory ratio and tire size works out to be. It isn't terrible but you're going to be turning much heavier tires. 4.56 would give you just a tad more than the factory Explorer. I personally would consider 4.56 the minimum that I would run with 33s and wouldn't hesitate to up it to 4.88 for a little performance.

Don't fear the gear!

Thanks Garry - BTW, when it comes to working on my wiring harness, I'll soon be studying your posts and videos.

 

[Tricky Dick]

I'm starting to lean that way @Tricky Dick since it's been suggested several times on this thread and several others....still have plenty of time to decide but that's my next big expense so I'm doing as much reading I can of others experiences. Even over at the explorer forum: https://www.explorerforum.com/forums/.

What works for Explorers is a good baseline until we get to higher speeds where our aero difference starts to matter more.

I just picked out ratios for mine and I was between 4.88 and 5.13 for 37s. In the end I knew what RPM ranges I wanted to be in so I held my nose and trusted the charts.

 

[Broncobowsher]

I'll reference it another way. A 302 at highway speeds, in a truck, is about 2000-2200 rpm. The more drag, the higher the rpm. So a clean (aero and rolling drag) bronco I aim for 2000 at 60. Scale that up, 90 mph is 3000 rpm. The drag of a bronco at 90 will need the torque of the engine turning 3000. And 75 is 2500 for the midway point.

Don't think mustang that will cruise at highway speeds just off idle. The aero and rolling drag are only a fraction of a bronco. Even the donor explorer has better aero and drag than a bronco.

 

[fordguy]

I would still recommend building just the rear axle and take it for a test drive before investing in gears for the front. If you find the 4.30 a bit soft, regearing the 9" is pretty affordable.

Speaking from experience, yes you would start with rear end only first

 

[Broncobowsher]

You can put together the Bronco with a gutted front axle, test drive it, then pull the front axle out and put in the final gear selection.

 

[76YETI]

Are the tires already on your truck? If so, measure them to be sure of the actual diameter.
It might be picking nits, but it’s always good to have the correct rpm to go by.

Stock Explorer engine? Or modified?
Stock-ish Bronco, other than the lift? Or heavier with bumpers and winch and racks and such?

Mine is in the middle, but mostly stock. I have 4.56’s with 31’s (with intentions of going larger) and it’s a rocket off the line. But too low for the highway. It still cruises fine with the flow, but would be much happier at a lower rpm level.
I bet mine would handle 3.50/3.54/3.55(whatever it is) just fine. But I think a 3.73 or 4.11 would be a better choice.

To that end, I have a couple of built 4.11’s to try on for size, but no time to swap them in.

I'll swap in the 4.11's to try them for you

 

[dmoses42]

I was in the same boat, almost. But I'm going with an AX15. I did all the same research you did, so I was torn between 4.30 and 4.56, and when I had the money to buy gears the 4.56 were cheaper for some reason, so that's what I bought. I can't give any reviews on performance since my gears are still on the shelf while I scrape enough money together for the AX15 conversion. And although you didn't ask, I bought Motive gears, they seem to be highly regarded from my research.