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

[skrit]

For those that don't know - this is an excellent resource for all questions gear / tire size related: http://www.grimmjeeper.com/gears.html

That being said, can someone with more knowledge than me explain "preferred" / "ideal" RPM values for STREET ONLY.

1. I want to step on the gas at a stop light and have my head snapped back as much as the Stock 5.0L EFI will allow.
2. Be able to quickly pass on a 55MPH two lane open country road dropping from 4th (Overdrive) to 3rd.
3. Cruise with normal traffic flow on the interstate highway going 70MPH.

ChatGPT says:

• City Driving: Around 1,500 to 2,500 RPM is common for smooth acceleration and efficiency.
• Highway Driving: Typically, 2,000 to 3,000 RPM provides a good balance of power and fuel efficiency.

There are a lot of RPM values in between those numbers so I'm trying to dial it in to best match my needs listed above and get the most enjoyment from the stock 5.0L.
I've not paid attention to my daily driver RPM's when driving so I'll take some notes on my way home from work today.

My individual results based on 5 gearing options are below. I added the 3.55 because that is what I currently have which will be changed.
UPDATED WITH ACTUAL TIRE DIAMETER OF 32.5"

 

[DirtDonk]

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.

 

[DirtDonk]

Oh, and fuel economy wise, mine is happiest between 55 and 60 (20-ish mpg) and goes down from there at 65 and above.
Stock everything up top. A little smallish on the exhaust side of things for max power, but does work great for all around driving.

Back to the gearing vs tire size, I try not to drive it much when it’s raining. Likes to swap ends with the Detroit Locker in the back.

 

[Bruners4]

I'm working through this same thing but have 4.10 installed already. I use 60, 70 & 80 MPH in that tool.
BFGOODRICH® ALL-TERRAIN T/A KO2 33X10.5R15 114R RWL Overall Diameter (in) = 32.5 and does have an effect on the RPM @ MPH calculations. My stock Big Bronco with the 5.8 likes the 70 MPH @ 1900 RPM and above. I don't have enough time with the Wagon's 5.0 / 4R70W yet to give my opinion. Most suggestions that I've heard are 4.56. Your front axle will limit your gear choices.

 

[Broncobowsher]

4.56 or maybe 4.30

The 4.88s with a torque built 351 was doable.but a little much on 33s. Full throttle passing would pull 6000 RPM and 100 mph in 3rd.

 

[bigmuddy]

With 33's and a 4R70W I would run at least a 4.30 gear but a 4.56 would likely be better.

I have the same tranny with a 351w and praying I can get away with the 4.56 gears running 35" tires. I wish I had 4.88s installed though.

 

[Yeller]

Watching responses. Currently have a v8 explorer with 31’s and 3.73’s. I think it’s fine but looking to go to 33’s.. yeah I can’t leave anything alone

I’m on a different board that GrimmJeeper is on as well, he’s very helpful with information

 

[skrit]

So my tires are the same as @Bruners4 which is in fact 32.5" diameter. Reducing the tire size by .5" increased RPM's around 30 for each combination. I UPDATED THE CHART ON MY OP. The engine will be completely stock and the Rig will be a soft top with a sport style roll cage, 23 gallon tank, full size spare tire in the back but no other heavy add-ons.

I used BlueDriver to monitor my commute this morning in my 2013 F150 3.5 EcoBoost 6 speed auto FX4 and I averaged:
2176 ROM @80MPH
2030 RPM @75MPH
1880 RPM @70MPH
1750 RPM @65MPH
I have no idea if this should be used as a reference or if this information is even useful. If the numbers on my daily driver are a decent reference for highway driving then a 3.73 would almost exactly match (numbers not shown but I did use the calculator).

My assumption though - 3.73 is ideal for highway but low end performance/off-the line acceleration would suffer. This is where I'm not really clear - how do you find the balance (which is why I'm asking the great folks here for opinions and advice). I'm not looking to build a rocket ship but...

Street driving only (for this discussion)

1. I want to step on the gas at a stop light and have my head snapped back as much as the Stock 5.0L EFI will allow.
2. Be able to quickly pass on a 55MPH two lane open country road dropping from 4th (Overdrive) to 3rd.
3. Cruise with normal traffic flow on the interstate highway going 70MPH (at a typical RPM level)

 

[Broncobowsher]

Ecoboost is a bad reference. DI engine has more low rpm torque in general. They are happier at lower RPM than an old school engine.

 

[Timmy390]

Ecoboost is a bad reference. DI engine has more low rpm torque in general. They are happier at lower RPM than an old school engine.

Torque range is a HUGE consideration when choosing gears with an OD transmission..........That's why I went with a low end torque cam......Having a W helps too......

Tim

 

[73azbronco]

for your number 1 question, you need the weight of a 90's mustang. Not a 4,500lb beast

 

[skrit]

for your number 1 question, you need the weight of a 90's mustang. Not a 4,500lb beast

 

[skrit]

Ecoboost is a bad reference. DI engine has more low rpm torque in general. They are happier at lower RPM than an old school engine.

Understood - I realized that after looking at torque charts for the ecoboost vs. the stock explorer 5.0 . Now that I've done some more reading and with other's experiences, I think I'm going to plan for a 4.30 ratio which seems like a sweet spot for my setup. Still have a long ways to go before that though.

 

[bigmuddy]

Understood - I realized that after looking at torque charts for the ecoboost vs. the stock explorer 5.0 . Now that I've done some more reading and with other's experiences, I think I'm going to plan for a 4.30 ratio which seems like a sweet spot for my setup. Still have a long ways to go before that though.

With a 4R70w I really think you will get by with the 4.30 but ultimately regret that ratio for "head snapping" power.

 

[Broncobowsher]

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.

 

[bigmuddy]

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.

Great idea!

 

[Bruners4]

/\ /\ What Broncowsher said!
Also make sure to use a ratio that you can also get for the front axle. There a quite a few gear sets for the 9" that are not available for the Dana 44 front.

 

[Yeller]

But anything within 3% is close enough. Many of the factory combinations are that far apart. I’ve done as much as 8% but the don’t recommend it for on road use.

 

[ntsqd]

Assuming that there is one, I like to look at the original application for the engine, gather the OEM tire size and the axle ratio. From there you can calculate what cruise rpm range is that the OEM intended. Use that RPM range as a target for your tire size.

I did exactly this with the '04 donor of the 5.3L going in the Wagon. 4.10's were a bit too tall, 4.56's were a bit too low (fine if I thought I'd be towing something like an Airstream), and the rareish D44 4.27's are just about perfect.

 

[Tricky Dick]

Watching responses. Currently have a v8 explorer with 31’s and 3.73’s. I think it’s fine but looking to go to 33’s.. yeah I can’t leave anything alone

I’m on a different board that GrimmJeeper is on as well, he’s very helpful with information

When I 302 swapped my old Sport Trac I did 4.10 and 33s, it scooted well and mpg was decent. But I also had a .80 OD, so slightly higher than the 4R70W.

I've also had a 4.0L Explorer with 33s and 4.56, it felt great. So I think you'll be happy splitting the difference with 4.30 skrit.