Gear ratio and tire size -

I’ve got a 3.8 JK on 33’s with the stock 3.21 gears. It’s EXTREMELY slow lol. But I’ve been daily driving it for 2 years and it’s livable. Adding 35’s you would be totally fine, you’d lose some pep but the badlands radio is pretty close to Jeep’s for 35’s (4.56).

37’s would get a little more of a preference thing. For Bronco to keep around stock Rpm’s you’d probably want to bump up to 4.88’s or 5.13’s. But with the 2.7 it would certainly be livable even with the 4.46 gears, there are tons of jeeps on 4.56’s and 37’s.

Also, just in general axle gearing is WAY more important for on road than off. When you’re talking about a 3x reduction in the transfer case, a slight difference in axle ratios doesn’t make a huge difference in the crawl ratio.

NickP

I’ve got a 3.8 JK on 33’s with the stock 3.21 gears. It’s EXTREMELY slow lol. But I’ve been daily driving it for 2 years and it’s livable. Adding 35’s you would be totally fine, you’d lose some pep but the badlands radio is pretty close to Jeep’s for 35’s (4.56).

37’s would get a little more of a preference thing. For Bronco to keep around stock Rpm’s you’d probably want to bump up to 4.88’s or 5.13’s. But with the 2.7 it would certainly be livable even with the 4.46 gears, there are tons of jeeps on 4.56’s and 37’s.

Also, just in general axle gearing is WAY more important for on road than off. When you’re talking about a 3x reduction in the transfer case, a slight difference in axle ratios doesn’t make a huge difference in the crawl ratio.

I will mainly use it to run 30-60 miles to a trailhead and then ride the rocky trails. Maybe 35's are a good compromise. I could run them for off road without a gear change and then change back to 33's for long distance road trips

These are the eternal questions of the universe. In all seriousness it depends on a lot of things. If you don't plan on any towing, don't go bigger than 35's, don't want to put on heavy bumpers, rooftop tents, or other items, and don't live at altitude in the mountains (like I do) you will be fine. Change any of those parameters and then you may need the 4.7 gearing.

For me, I live at high altitude and drive mountain passes daily. Acceleration and power in the thinner air calls for the taller gears. I see the tourists Jeeps tricked out with tens of thousands of dollars in bumpers, winches, wheels, tires, tents, fuel cans, antennas, cb's, racks, cages, round lights, square lights, and some trailers. Almost all of them can't get out of there own way going up an incline. They have those Jeeps screaming at redline just to keep up with traffic. Re-gearing is a must for Jeeps (though there new Recon package for 2022 is finally addressing this thanks to Bronco. Jeep is putting in 4.56 gearing). Personally I feel if you are going to have any of those limitations and especially if you are going with the 37's then you need the sasquatch gearing. Ford didn't engineer it that way for shits and giggles.

Since you're looking at the 2.7, that means you'll have the auto trans. The 4.47 will be fine on road and off, regardless of tire size. With the auto, the differential gearing is much more forgiving. You have the ability to add brake or accelerator and very easily go between the two. Going deeper than 4.47 would only matter on the most difficult of trails, and even then, only with 37"+ tires. To be perfectly frank or candid, the 4.47 and 4.7 gearing is more about marketing than usefulness. It was offered to beat the competition. It's really low for a daily driver, almost too low for those with a manual transmission and daily driver. Off road, will it move the vehicle forward when there is traction, and break loose when there isn't? Will it go slow enough over the rocks (you have the auto, so it'll go as slow as you let it).

So many buyers of these vehicle will never use them (regularly) off road, such that the gearing and tire size isn't important or relevant to how the vehicle is really used. Don't stress or worry about it, because ultimately going from 4.2 or 4.7 or 4.47 won't be the reason you aren't having fun, and it won't be the difference between "screaming at redline" just to keep up with traffic. As a matter of fact, a vehicle with 35" tires and traveling 70 mph is at about 3,000 rpm in 3rd or 4th gear, so it isn't screaming at all, it's in its most effective RPM range. Red line is close to 7,000 rpm, so they aren't screaming to keep up with traffic, unless traffic is going 140 mph or so.

4.2 to 4.47 is 6%. That's not going to make much difference. It's plus or minus 120 rpm if you'd normally be running at 2,000 rpm.
4.47 to 4.7 is 5%. Again, that's not much, and it won't make an appreciable difference.

4.2 to 4.7 is appreciable, but really only off road, and much more so if you're using a manual transmission.

33" to 35" is 6%.
35" to 37" is 5%.

33" to 37" is appreciable, but unnecessary.

Everyone always thinks of regearing in relationship to tire diameter only but you also have to take into consideration additional rotating mass. A move from 32” factory size to 37” is going to add another 25-30lbs per tire (and that’s assuming the new wheels weigh the same as the factory set) of unsprung, rotational weight. Regearing helps tremendously with the engines ability to spin up that extra mass.

You have to ask yourself, “how big of a turd am I willing to drive?” The answer for a LOT of Jeep owners is apparently a pretty big one based on my experience. Meanwhile, I’ve regeared every vehicle I’ve ever lifted because I hate sluggish turds.

johndeerefarmer

I am looking to get a 2.7 ecoboost, Badlands with the stock 33's and 4.47 rear end.
If I add 35's the effective rear end will probably be a 4.2. How will this be for rock crawling as well as general driving?
Then if I get gung-ho and add 37's the rear end will be more like a 3.9. Now how will it be for rock crawling and general driving?

I'd run 4.47 on 37's with my flat brim hat on. It would probably piss a few off but hey its how I roll.

Anything less you'll feel like your driving a tacoma.

Keep in mind everyone who orders a Badlands with SAS is going to be on the highway and off-road with 35" from the factory. On my 71' with np435 four speed, 4.11 gears and T shift transfer case, I'm running the same crawl ratio as the 2021 auto transmission is with the 4.47 gears. The tire height is not figured into any of that, other than for ground clearance. Crawl ratio is independent of tire height. I run 33" tires year around except for when I crawl I put on a set of 36" wheels/tires. Now when rolling down the highway yes, tire height effects the RPMs of course and how it feels driving etc as far as sluggish, pep, etc, but even then the crawl ratio is the same. Also, once someone gets into the 37" tire size and above, things start to break with an aggressive driver, heavy foot, and not low enough gears. 37" and bigger is when you see folks step up from the Dana 44 front axles to the Dana 60 axles and move into the 5.13 gear sets. Not always of course, but it's very common.

ChetC

Everyone always thinks of regearing in relationship to tire diameter only but you also have to take into consideration additional rotating mass. A move from 32” factory size to 37” is going to add another 25-30lbs per tire (and that’s assuming the new wheels weigh the same as the factory set) of unsprung, rotational weight. Regearing helps tremendously with the engines ability to spin up that extra mass.

You have to ask yourself, “how big of a turd am I willing to drive?” The answer for a LOT of Jeep owners is apparently a pretty big one based on my experience. Meanwhile, I’ve re-geared every vehicle I’ve ever lifted because I hate sluggish turds.

Yes it is a lot more more than simply looking at tire diameter and gear ratio. In reality this will matter to many more people than you would think. It's unfortunate most dealer sales people are not well versed in the practical application of gearing. It's like death by 1000 cuts, you add this to your rig, add that, change tire size, etc., and you don't notice how crappy the performance of a once spirited car becomes with each little item degrading performance. Then you get in a friends newer car or in one or one that is properly geared and you wonder why yours sucks so much.

Each person needs to really understand what they plan on doing as far as equipping their Bronco. If you go by it's only 5% less efficient or change in final drive you will be sorely disappointed in the end. Of course you can always re-gear later butt it sure is nice having a factory option. It's why Jeep is finally jumping on the Bronco train.

Why would the manufacturer or sales person assume everyone is going to put all of the available aftermarket things on the vehicle, and build for that? People that buy every accessory are the ones self-inflicting the death by 1,000 cuts. Think you need steel bumpers, nope. Think you need a winch, nope. Think you need a roof-top tent...or a new spare tire carrier or extra fuel or a refrigerator? The answer, honestly, is nope. (Almost) everyone worrying about gearing and off road performance aren't going to truly need to worry about their gearing because they're driving the kids to school, not across the Rubicon, but across the neighborhood.

Honestly, think about your use and if you're truly a 1%'er, then worry about what gearing your rig comes with stock. Otherwise, it's not really that important. If you're a 1%'er then the price of a re-gear is irrelevant.

BTW, Jeep isn't jumping on the train. You could order Rubicon axles with 4.56, 4.88, 5.13 and 5.38 gearing through the Jeep Performance Catalog long before the Bronco came out. You could order bead locks too. The 2018 Jeep Wrangler was designed to accommodate 35" tires from the factory, fender flares and rock rails designed for more clearance. Know why Jeep could offer the Extreme Recon package and deliver it before the Bronco? It's because the vehicle was already designed to accommodate all of those parts, and all of those parts were already sitting on the shelf. Jeep offered the factory lift, axles/gearing, wheels, and designed the vehicle prior to the 2018-roll out for all of it.

If you're really interested in off road, you want to shed weight, not add weight.

It's getting very 6G in here.

I had a 2013 JKU Sport that I put 37s and 5.38 gears on a well as a plethora of Poison Spyder bumpers and whatnot. I was a huge fan of that setup and don't have anything bad to say about it. I've since gotten rid of that Jeep and now have a Bronco coming. It's a Badlands Sasquatch, so 35s and 4.7 gears. Until drive it the way I'm going to drive it I won't know what I want to do with it but for now it will stay stock. Iwill be pulling a Patriot X3 camper and will be more "overlanding" than I will rock crawling but I want a low enough gear and enough ground clearance to get up and around some mountain passes offroad as well as remote locations. This 10 speed transmission and 2.7 are much different than what the JKU had so it not comparing apples and apples.