4.80, 5.13. 5.38 ratio.

[Texasgrillchef]

I currently have the badlands 2.7, Sasquatch bronco. 4.7 ratio. 35” tires.

i was thinking of moving up to 4.88, 5.13, or even 5.38. I know if have to do it for both front and rear.

I want to eventually upgrade to 37” tires. But not at the same time I do the gear upgrade either. I would rather do the gear up grade first followed later by the tires rather then vice versa.

as someone else mentioned in another thread. That the mechanical workload of 33” tires with a lower ratio was equal to 35” with the 4.7.

So if I move up to 37’s which would maintain equal mechanical workload? The 4.88, 5.13, or the 5.38?

Other than gas mileage which is not a huge concern to me. And lower top speeds on highways. What other considerations should I think about when choosing either 4.88, 5.13, or 5.38?

I also sometimes pull a 2500lb off road trailer that allready as 37 tires on it When I overland.

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[kodiakisland]

If you are going through the expense, go as low as you can. No one ever wished they went higher. Both the manual and the auto transmission are well served with lower than factory final ratios.
Just get the 5.38s and don't look back.

 

[indio22]

With manual trans and 35" tires, I'd be leaning towards 5.13 diffs. Leastways that would basically get me back to what I had with stock 30" tires and 4.46 diffs.

With 37" tires some forum members are running 5.13 or 5.38 diffs.

 

[Tricky Mike]

Nitro has a 5.29 kit as well to consider. I'll be doing that or 5.38, which will still be very drivable on 35s with these super deep overdrives we have.

I would scratch 4.88 off the list completely, very little gain for the expense.

 

[HoosierDaddy]

With manual trans and 35" tires, I'd be leaning towards 5.13 diffs. Leastways that would basically get me back to what I had with stock 30" tires and 4.46 diffs.

But that 1st gear is soo short when it was on 30's !!!!
LOL!!

Anymore , I tend to look at what RPM's I would be turning at 78/80mph in 6th with a given tire gear combo.

The logic behind that is how well this thing runs and how much my fuel mileage improved running it at 2600/2700 rpm in 5th gear on the Interstates.
So, 35's would need a 5.38 and 37's would still run out really well also. Good thing, as I haven't seen anything deeper than a 5.38, ..... which just sounds insane! LOL

I then compared that ring gear & rpm to the factory set up across all the gears, I usually ended up being even lower geared in 1st than the factory was.

Not sure how I'd like that, but 2nd gear launches might be the thing then. LOL
2 granny gears for the win!!!!

https://www.grimmjeeper.com/gears.html

 

[Tricky Mike]

I usually ended up being even lower geared in 1st than the factory was.

IMO factory gearing is too high for most trims so this tracks. It helps offset the weight gain to over correct too.

 

[indio22]

But that 1st gear is soo short when it was on 30's !!!!
LOL!!

Anymore , I tend to look at what RPM's I would be turning at 78/80mph in 6th with a given tire gear combo.

The logic behind that is how well this thing runs and how much my fuel mileage improved running it at 2600/2700 rpm in 5th gear on the Interstates.
So, 35's would need a 5.38 and 37's would still run out really well also. Good thing, as I haven't seen anything deeper than a 5.38, ..... which just sounds insane! LOL

I then compared that ring gear & rpm to the factory set up across all the gears, I usually ended up being even lower geared in 1st than the factory was.

Not sure how I'd like that, but 2nd gear launches might be the thing then. LOL
2 granny gears for the win!!!!

https://www.grimmjeeper.com/gears.html

Yes, seems difficult to accommodate both 1st and 6th gear with the diff choice. Since switching to 35" tires with the stock 4.46 diffs, I like first gear more. But now 6th is compromised. Choosing 5.13 vs 5.38 diffs would depend on which of the gears might be compromised.

 

[RagnarKon]

So if I move up to 37’s which would maintain equal mechanical workload? The 4.88, 5.13, or the 5.38?

The answer to this question is 4.88. But to be frank, I don't think the cost to upgrade is worth it unless you go to 5.13.

I have a Bronco RPM calculator you're welcome to play around with.

 

[Texasgrillchef]

Yes, seems difficult to accommodate both 1st and 6th gear with the diff choice. Since switching to 35" tires with the stock 4.46 diffs, I like first gear more. But now 6th is compromised. Choosing 5.13 vs 5.38 diffs would depend on which of the gears might be compromised.

I have stock 4.7’s though on my 35’s right now I have achieved a top speed on level ground here in Texas, with no wind of about 100mph I think ford limits the speed for some reason.

i have full auto, so I have the 10 speed transmission. like I said I do have a trailer I pull on over landing which includes some rock crawling with the trailer sometimes too. So the extra low gear power would be nice

 

[Texasgrillchef]

But that 1st gear is soo short when it was on 30's !!!!
LOL!!

Anymore , I tend to look at what RPM's I would be turning at 78/80mph in 6th with a given tire gear combo.

The logic behind that is how well this thing runs and how much my fuel mileage improved running it at 2600/2700 rpm in 5th gear on the Interstates.
So, 35's would need a 5.38 and 37's would still run out really well also. Good thing, as I haven't seen anything deeper than a 5.38, ..... which just sounds insane! LOL

I then compared that ring gear & rpm to the factory set up across all the gears, I usually ended up being even lower geared in 1st than the factory was.

Not sure how I'd like that, but 2nd gear launches might be the thing then. LOL
2 granny gears for the win!!!!

https://www.grimmjeeper.com/gears.html

well I do like the thought of the extra power in the lower gears, especially when I am either doing major rock crawling or minor rock crawling with my over landing trailer.

while currently on my 4.7 stock and 35” tires stock. I can get 100mph top speed without trailer. I would still like to be able to easily maintain 80-85 mph speed without topping out the rpm. In Texas we still have a few roads with 85mph speed limits.
I do have the 10speed auto transmission and the 2.7 engine.
i also do care to much about gas mileage for the most part. I’d like to keep it above 10mpg if possible though.

 

[Texasgrillchef]

When I use the RPM calculator. Cool calculator by the way. It really shows that sometimes rpm isn’t the only thing to be considered though.

I put in 1st gear, and say 1mph. It shows very low rpm across the board. But if you’re just idling. Especially on the auto trans it’s not going to kill the engine. Also if your rock crawling. Put your foot on the gas and it will increase rpms but not necessarily speed.

What the calculator doesn’t account for is vehicle resistance caused by wind, going up a hill or over a rock, or even pulling a trailer.

regardless of tire size we all know that the lower the gear ration. Higher the number. The more power we will have in first gear. Even in 10th we will have more power. More torque To the wheels but less speed.

so as several of you have pointed out. It is a trade off. We get more power less speed, and poor gas mileage. Although I’m not as concerned about gas mileage.

i do care about top speed though. and I do care about power in lower gears. Especially when minor rock crawling with my trailer and going up hills as well.

in a perfect world I would love to be able to maintain 85-90 mph while pulling my trailer, and still have decent power pulling my trailer up steep hills and minor rock crawling.

i would rather do the tire upgrade and gear upgrade separately but if I can’t then so be it. Problem with going to 37’s is other things have to be done as well besides gearing upgrades. Which increases cost.

i estimate about 15,000 miles left on my stock 35” good year tires before time to invest in 37’s.

 

[Texasgrillchef]

Yes, seems difficult to accommodate both 1st and 6th gear with the diff choice. Since switching to 35" tires with the stock 4.46 diffs, I like first gear more. But now 6th is compromised. Choosing 5.13 vs 5.38 diffs would depend on which of the gears might be compromised.

just out of curiosity why did you say choose the 6th gear when the auto has full 10 gears? Wouldn’t it be easier to find a gearing match accomodation if you say did 1st and say even 8th or maybe even including the 10th?

 

[RagnarKon]

I put in 1st gear, and say 1mph. It shows very low rpm across the board. But if you’re just idling. Especially on the auto trans it’s not going to kill the engine. Also if your rock crawling. Put your foot on the gas and it will increase rpms but not necessarily speed.

What the calculator doesn’t account for is vehicle resistance caused by wind, going up a hill or over a rock, or even pulling a trailer.

It will account for wind, going up a hill, going over a rock, pulling a trailer, etc. The only thing it doesn't account for is slips in the torque converter (clutch for those manual users) or traction losses. The calculator is basically assuming that the engine is connected directly to the transmission at all times, and the wheels are connected to the ground at all times.

But regardless, I will agree that it's only part of the picture. You really need to combine that calculator with a horsepower/torque curve to get a real sense for things.

i do care about top speed though. and I do care about power in lower gears. Especially when minor rock crawling with my trailer and going up hills as well.

in a perfect world I would love to be able to maintain 85-90 mph while pulling my trailer, and still have decent power pulling my trailer up steep hills and minor rock crawling.

i would rather do the tire upgrade and gear upgrade separately but if I can’t then so be it. Problem with going to 37’s is other things have to be done as well besides gearing upgrades. Which increases cost.

Perhaps unpopular opinion, but I'd personally do 37s before regearing.

That'll give you the opportunity to get a sense for what the shortcomings are. If the low speed performance is really bad maybe you'll want to do 5.38 or 5.13. If it's fine, maybe makes sense to do 4.88 or just stick with 4.70 for more of that top-end speed.

 

[Texasgrillchef]

It will account for wind, going up a hill, going over a rock, pulling a trailer, etc. The only thing it doesn't account for is slips in the torque converter (clutch for those manual users) or traction losses. The calculator is basically assuming that the engine is connected directly to the transmission at all times, and the wheels are connected to the ground at all times.

But regardless, I will agree that it's only part of the picture. You really need to combine that calculator with a horsepower/torque curve to get a real sense for things.


Perhaps unpopular opinion, but I'd personally do 37s before regearing.

That'll give you the opportunity to get a sense for what the shortcomings are. If the low speed performance is really bad maybe you'll want to do 5.38 or 5.13. If it's fine, maybe makes sense to do 4.88 or just stick with 4.70 for more of that top-end speed.

All of that makes sense to me. And true going with the 37’s first would give me an idea of both top speed as well as power levels in first gear on my current 4.77’s. All of which would give me a better idea of what to go with later of 4.88, 5.13 or even 5.38.

if top speed sucks really badly, AND if I am really under powered in first gear. Then go with 5.38.

if top speed and 1st gear power are only slightly bad go with the the 4.88. Or maybe eve 5.13.

 

[Dusty]

I recently re-geared to 5.13 with 37's (2-door 2.3L/7MT) and in my opinion it's the perfect gearing for that combo. It rock crawls like a champ and does well in all gears on the freeway.

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