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Transmission Gearing Question

Comadivine11

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I'm not super versed in gearing, but from what I understand, any changes up or down from stock tire size would theoretically require re-gearing for optimization, correct? For example, the manual BL comes with 33" tires and a 4.7 final drive ratio but if you wanted to go up to 35s non-squatch, you'd have to go up to 5.13 or something, even though 4.7 is the gearing for sasquatch with 35s, eh?

Second question; I had an '04 MT Rubicon that came with a 4.11 gearing and I would often start in second gear because the first gear was so short you had to shift by like 6 mph. Do you think the MT Bronco will have a similar, very short first gear?

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Philly

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I think that the crawler gear is supposed to fix the short first gear. It is below first so you never really shift into it unless you are planning to use it.

I also do not think you will need to go above 4.70 for 35's regardless off transmission. With the Jeep JK's, all of the manual guys ran higher (numerically lower) gearing than the auto guys. My gutless 2010 JKU with the 3.8 V6, 42RLE auto trans, and 35x12.50r15's on it would be great with 4.88's or 5.13's, but I never ended up regearing. It has 3.73's stock and has been bearable with a tune, but you aren't going anywhere fast.

If I remember correctly, many of the manual guys with the same setup didn't go past 4.56 gearing and when the 3.6 V6 Pentastar came out, pretty much nobody with a Rubicon (4.10's) even bothered swapping gears.

Ford's engines are also much more powerful than that old 3.8 and these new transmissions are better so nothing should have to work as hard or need to compensate so much with gearing.

The most important thing you will need to do when bumping up tire size is reflash or tune your transmission so it shifts properly. I use a Superchips Flashpaq in my jeep and have never had an issue with it. This also corrects your speedometer for the larger diameter tires.

Bottom line, could you regear? Yes. Do you need to? Probably not. If you're worried, wait for someone else to do it and post the results up here first.
 

Philly

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@Philly Thanks for the detailed response!
No problem! Figuring out the correct gearing is such a pain. A lot of posts will come down to a couple different ratios that depend on how you plan to use the vehicle and what you like.

Makes it hard to find out what the right gearing is for your setup.
 

kodiakisland

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Really, it depends on what performance you are willing to put up with. Many people describe their vehicle as slow, gutless, lacking power, etc. It’s the gears that cause that. If you don’t mind, then go with it. You don’t need to or have to, but long term you might be happier if you did.

For those who do more highway driving than off-road or city, the high gears may never be an issue. I will always go too low than too high on my vehicles because they rarely see the interstate, and I hate a vehicle with poor acceleration.
 

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Wouldn't Ford have the proper recommendations based on wheel/tire size? I ask since I've always had the same questions surrounding gearing ....
 

kodiakisland

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Wouldn't Ford have the proper recommendations based on wheel/tire size? I ask since I've always had the same questions surrounding gearing ....

Proper for who?

Manufacturers use the gears that will placate most consumers as well as the EPA. Doesn't always mean it's the best for you though. I always get the lowest option, because I know for my needs and desires, the standard gears are usually too high.
 

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Proper for who?

Manufacturers use the gears that will placate most consumers as well as the EPA. Doesn't always mean it's the best for you though. I always get the lowest option, because I know for my needs and desires, the standard gears are usually too high.
You will be fine with the 4.70s for the 35s. Gearing depends on a lot of factors. I ran 410s on 40s, 538s on 32s and 488s on 35s.
 

Hoofnmouth

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4.56 should be enough for 35 to 37 but these new multi speed autos are finicky and will hunt for the right gear if its not optimal
 

Mopar2Bronco2021

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You will be fine with the 4.70s for the 35s. Gearing depends on a lot of factors. I ran 410s on 40s, 538s on 32s and 488s on 35s.
Do you think it would be SAFE to try out 35s on the 4.46 gearing with the 10 speed auto? I know there’s a lot of variables to consider which is hard to do on a vehicle none of us have driven. I’d still like an opinion from some of you more seasoned guys though.
 

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Do you think it would be SAFE to try out 35s on the 4.46 gearing with the 10 speed auto? I know there’s a lot of variables to consider which is hard to do on a vehicle none of us have driven. I’d still like an opinion from some of you more seasoned guys though.
I feel 35s will be fine. If you go to 37s re-gear.
 

kodiakisland

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Do you think it would be SAFE to try out 35s on the 4.46 gearing with the 10 speed auto? I know there’s a lot of variables to consider which is hard to do on a vehicle none of us have driven. I’d still like an opinion from some of you more seasoned guys though.

Sure it will be safe. The only downside will be lack of power and slow acceleration. Many here think that's acceptable. You may too.
 

Hoofnmouth

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Regearing isnt the end of the world either do it then your done ifs kinda a pain but rear will be straight fwd.
 

Shirt8u1

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Proper for who?

Manufacturers use the gears that will placate most consumers as well as the EPA. Doesn't always mean it's the best for you though. I always get the lowest option, because I know for my needs and desires, the standard gears are usually too high.
Same here
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