Wanting to go to 40s

[Headbarcode]

That's how this place works, the OP will get an answer somewhere but it'll be lost in a sea of other conversations lol.

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[J0E]

To the OP...You’ve been on these forums since 2020, plenty long enough to have read the numerous threads on 40’s and requirements. It’s an expensive step to make, but plenty have done it and have documented how to do it. ??

I was about to make the same comment. Too lazy to dig up this common topic?

If it bothers you that much that someone posts looking for advice, why you read or respond. Keep scrolling and save yourself the headache. Merry Christmas!

Wow, first you're too lazy for due diligence, then you attack a reasonable question. And then you don't bother to follow up to the others who missed you're a mall crawler and want 40's for looks.

Merry Christmas everyone!!

I currently have 37 in nittos and will be replacing them shortly after the new year. I’d really like to go to 40s for height and look. My jeep is a 2020 JLU Rubicon. Gears and axels are stock. It’s got a 2.5 inch lift already. I know gears will have to go to at least a 5.13 I think. Will I need to add more lift and upgrade Axels?

How many people that are running 40s did not go to hydro steering? I know that there have been many times with 37s that my JL has not been able to turn the tires without backing up and pulling forward to be able to get the tires to change direction.

Aired down to 13.5 PSI on 37's, I frequently can't turn the wheel. I don't yank on it real hard because I'm afraid I'll break some steering component. Others conjecture I can yank as hard as I like, it won't break any thing from the factory steering.

Posted about this before, but talking to many old timers that went to 40's etc. almost all without an exception said they would have stayed with 35s and just really good components. As stated here by those more experienced in the matter, unless you have money to burn and just love wrenching on something you don't need to be available all the time to get you around, going to 40's is going to easily cost you the same amount again as you paid for the Jeep.

You also aren't really buying that much more capability, A well done Jeep with 35's and a lift is going to be able to do almost anything someone with 2.5 more inches of pumpkin clearance is going to do and is way more likely to not break something doing it.

That said, if you like the looks and have the money, go for it. If I had a standby mechanic and 100K to sink into the Jeep with a good tow vehicle to get it to different states, I would for sure!

> You also aren't really buying that much more capability, A well done Jeep with 35's and a lift is going to be able to do almost anything someone with 2.5 more inches of pumpkin clearance is going to do and is way more likely to not break something doing it.

Right, and a well done Jeep on 30s is going to be able to do almost anything someone with 2.5 more inches of pumpkin clearance is going to do and is way more likely to not break something doing it.

The breakage part is true, the capability is obviously false.

Towing the Jeep behind my ram rebel from here to CO and back we averaged 8mpg…I’ve yet to find this mythical location out west that gas is more than 150 miles away from the last station though? Sure some stretches out in the desert are 70-90 miles between stations, but unless you’re getting less than 5mpg I still argue you can get anywhere comfortably. If the OP is going to run a light 40 like a bfg or milestar vs the heavy nitto 37’s he currently runs, I doubt he’ll see more than a 10% drop in fuel economy anyway. 12-13mpg still gives an effective range of 240-260 miles which is more than enough to get anywhere in this country. The Mojave road is one of the longest trails I’ve ever seen and it’s only 100 miles from end to end, not to mention there are at least 3 locations along it where you only need venture a few miles off course to a fuel station. You could likely run the entire thing with a 5 gallon tank getting 5mpg if you stopped at every available station. On 38’s we averaged 15mpg. Fueled up in Merced, drove 100 miles up a mountain from 100’ elevation to 10k’, not realizing the fuel stations in shaver lake were not 24hrs. Ran the entire Dusy Erishim trail 40 miles in 4LO, and still made it the 30 miles back to town. Fuel issues in a vehicle with a 20 gallon tank that gets even high single digit mpgs are a myth. Would it be nice to go 400 miles between fill ups? Absolutely, but it’s far from necessary. I haven’t run 40’s on a JL, but even on 38x13.50’s running all those trails you mentioned, our experience has been much more durable than what you described. The stock ball joints lasted 35k miles. Still had stock axle shafts, rear drive shaft, rear track bar and tie rod at 62k miles. Front driveshaft needed replaced after flexing it out too many times on 29” long front shocks. I’m not saying 40’s are perfect on stock axles, but we’ve all seen people running 40’s without major upgrades or issues on this forum just as we’ve seen people destroy their axles on stock tires. The idea that there’s some magic leap from 37/38’s to 40’s ignores all other factors from weight to driving style. Odds are 39’s will be our next tire choice on the XR, and I’ll be sure to keep everyone updated on failures and/or success.

> If the OP is going to run a light 40 like a bfg or milestar vs the heavy nitto 37’s he currently runs, I doubt he’ll see more than a 10% drop in fuel economy anyway

The increase in rotational inertia is insignificant compared to the inertia of the vehicle. Rotational inertia only occurs under acceleration. That's why mag's were invented. Under extreme acceleration, magnesium wheels had significantly less rotational inertia than a steel wheel. There is no rotation inertia change at steady state, ie on the interstate at 75 MPH. Many have speculated the biggest factor in MPG decrease from larger tires is due to decreased aerodynamics.

My JLR 2.0 auto went from 22 MPG stock to 20 MPG on 37 KM3's, same wheels, gears, only tazered.

 

[Headbarcode]

How many people that are running 40s did not go to hydro steering? I know that there have been many times with 37s that my JL has not been able to turn the tires without backing up and pulling forward to be able to get the tires to change direction.

I've yet to go hydro on mine because they don't seem to offer a kit for the 2.0 with etorque.

I was at 12-13psi in my 40x13.5's and didn't notice any more resistance offroad than at 32psi on pavement. It wasn't until I was loaded up into and climbing boulders, before I lost the ability to turn the tires. As soon as the tire crested the climb, I was able to turn again.

 

[Speed331]

It’s not uncommon for some of our most rural areas to have a single gas station with limited hours. It’s also fairly common to find people out of gas on those stretches because they miscalculated, or counted on a station that was closed after 5:00 pm, or rural station was out of fuel.

Been there, done that. Spent a fridged 6 hours huddled in the front seat of a truck with my best friend in Ely back in the early 90's. On our way to Montana and hit Ely about 11:15 with 1/8 of a tank left, only to find everything closed at 10 - and didn't open until 6am. It was early March and the temp was in the mid 30's.
It's a great story now, but it sucked at the time.
There's way more abundent services out there now for sure, but you can still get caught out while passing through real rural areas...

 

[XtremeRetard]

Hydro or at least Redneck Ram equiv and Apex boost seems to be what PSC do now for the jl and etorque etc. However it's an assist so if you just haul arse on the wheel you get the same effect with way more effort.

Also consider that you are less likely to break tie rods, ball joints, pitman arms, drag links etc if you wriggle forward and back to manually turn the wheels.

I think with extra power assist is easier to bust steering stuff.

I do 8 rated trails on 37s with no assist 7psi beadlocks. And steering sucks at times, but just wriggle forward and back and all is well.

With axles and upgraded steering then sure, boost the crap out of the steering. But stock, I think you are just rolling the dice each time you force it with the factory components.

 

[Jhawth]

C'mon guys!!!... the OP wants to know if it is ok to run 40s for height and looks and you lost it discussing towing, 800 rated trails, mileage.. gas stations between Anchorage and Baja, and jumping 20 feet in the air.... LOL.. sure.. you can run 40s on 2.5 lift for looks.. but if you wheel hard then of course 1 tons and upgrade basically everything on your JL is the logical and sensible thing to to....I am one of those idiots who run crazy heavy 40s on stock axles (with front axle truss) .. I also have PSC hydro assist.. but yeah.. running 40s on stock for looks is OK .. on the trail 40s definitely have an edge over 37s..

OP.. can you be more specific? why do you want to jump to 40s? do you rock crawl?.. drive a lot of miles per year?

But the real question is...


What kind of oil should I use if I'm running 40s and how often should I change the oil? Also, is the 2.0 or 3.6 better? ?

 

[XtremeRetard]

Walmart extra virgin olive oil for sure!

 

[Infidel09]

2021 Jeep Wrangler 392 - 40" tires Tuned motor and transmission suspension upgrades are minimal. 2" spacer front coil with drop control arm brackets. Adjustable control arms are next... In the rear 1/2" coil spacer - I have a Trek top soft top the weight reduction lifted the Jeep another 1/2".

 

[3TV]

Nice Jeep Infidel. I've got my 392 on 40s as well. It drives better than it did on 37s, probably because the suspension is tuned better this time around. I get 11 to 14 mpg on the interstate with the 80-mph speed limit around here. And I have noticed no difference in steering effort between 37s and 40s. I installed an Apex steering boost kit because the steering wasn't strong enough for 37s, and the boost kit seems to be working just as good with 40s. Even stock 4.56 gearing is fine with 40s. The 392 has enough torque that it doesn't seem to care about gearing.

Something else to think about with axle strength, at least with a 392 XR. The front axle is stronger than a regular Rubicon axle. The wall thickness of the tubes is 43% greater (10 mm instead of 7 mm). It doesn't have the FAD, which is a weak link. The CV joints in the 392 front axles are stronger than the u-joints in a regular Rubicon front axle. They aren't as strong as RCV CV joints, but people are not breaking the stock front CVs in 392s running 38s to 40s. It has cast iron knuckles instead of aluminum. It has bigger brakes. And it comes with the 4.56 gears.

Here's mine. A 4 1/2" Metalcloak lift, but on stock axles for now, with Dynatrac ball joints, MetalCloak track bar, drag link, and tie rod, and Metalcloak sector shaft brace and track bar brace, and Fox ATS.

 

[Max Headroom]

The JL shows the Jeep empty at 17 gallons. Yes I am aware the tank is 21 gallons before it stops running. Done that. 8 mpg in a relatively flat Michigan towing a camper. Running HYW 50 across norther Utah and Nevada there are places that 168 miles may not be enough. I think I counted 11 or 12 mountain passes from Moab to Reno. I would not be getting 8 mpg pulling the camper over mountain passes. I could easily be down around 5 mpg. There are places in California where gas can be 150 miles between stations also.

For those not familiar with the high desert between Oregon and Nevada there is a stretch between Lakeview, OR and Winnemucca, NV that has a hot, grueling 211 miles without fuel.

Also there are places where you don’t necessarily know that fuel is available because it might be 5 to 10 miles out of your way to get the fuel, so you don’t stop and you pull in to a gas station and take 20.4 gallons of fuel with the next fuel stop 78 miles away.

This also means you can not wheel or explore at all between these stretches because of the lack of fuel. An extra 5 gallons of fuel mean 40 more miles at 8 mpg.

Just because you don’t think these places don’t exist, does not mean you are correct.

Then of course any of these places you could easily have heavy head winds that can drastically impact mileage.

The situation is better than it used to be. There are fewer of these stretches than there were 20-30 years ago. But plenty still left and sometimes that one station that breaks up these big stretches isn't open, or doesn't have the fuel you need. Or there's a huge headwind that kills your already poor mileage...

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