I used this online calculator from tiresize.com and going from 33" to 35" decreases the effective ratio of 4.1 gears to 3.83 so you are close in calculations. I felt the change after going to 35" but it wasn't terrible as some make you think. Would I like to regear to 4.88? Yes, but after adding an AFE Scorcher GT module, it helped quite a bit, so regearing is in the back burner for now. Shifting feels better and the truck isn't hunting for gears or downshifting as much as post tires, pre Scorcher, when towing our Geo Pro 19BH which is about 4,000LBS loaded.
I would agree on stock axles, but when they say larger axles I'm assuming they are 60s at a minium. That's a much higher load capacity than the stock axles, much larger brakes than stock, and all of the added weight is unsprung and therefore not affecting the load carrying capabilities of the frame/ chassis itself. I know the official gcwr doesn't change but their mods would make me more comfortable towing at the limit than I'd be in a bone stock gladiator.
From a practical standpoint, completely agree. There's 100 things you can do to make towing more comfortable, but at the end of the day liability and legal issues are what they are, and you have to remember the GCWR. Get in a wreck while towing and I promise the insurance lawyers will look for every single excuse to deny your claim, it's what they are paid to do.
Of course any wreck big enough to warrant a full on investigation is big enough that travel trailer is a pile of kindling so good luck getting an accurate weight of exactly how much I was towing anyway. This debate has gone on on forums for years and I've yet to see one example of a denied claim. Even if you're illegally towing over the limit, you're still covered. Just like if you're driving over the speed limit, made an unsafe lane change, or even if you're drunk. Insurance covers illegal and stupid both, which is pretty much the cause of every accident anyway.
Your math and description of load on the engine would make perfect sense if it was direct drive or the transmission was in the same gear at a given speed for the given load. Fortunately there's an 8 speed which will easily compensate for the larger diameter tire by simply downshifting. Every JLU comes with a 3500lb tow rating and they come stock with everything from 32" tires to 35s. Everything from 3.45 axle gears to 4.88s. Almost as though the transmission is compensating for both gearing and tie size... because it is. The fact that the JLU ecodiesels and the saharas with 3.45s and the v6 got the same tow rating is enough proof that the tow rating isn't gearing or power related. As you've noted they are coming system limited, which shouldn't be an issue on the baby hills back east.The basic hillbilly math below for torque loss from bigger tires is an estimate but will give you an idea of what tires add to the load on the engine:
difference in tire size/OG tire size*rated torque
My truck, I pull a 2600ish Opus on 40's with stock gearing (3.73)
7/33*420=89.09 lb ft loss. Which is 21%... And I'm not geared so I have to take that right out of my GVW rating to compensate. My Opus is at the upper limit of what I should try to pull with my current setup. ( truck is 6200 by itself which is 250 from the GVWR of just the truck, take 21% off the 5K tow rating of the Eco D down to 4K and then to be safe, not more than 70% of max tow, is 2800 lbs, which is just over what my trailer is. I'm maxed out at this point.
Asking the engine to turn a bigger diameter merry go round adds significant leverage against the motor crank for it to overcome. Plus the whole tire/wheel package is heavier as well.
My truck does it but not particularly well. Always watching the engine oil temp and boost temps cuz it doesn't take long for those to crank up when hitting a hill here in CO. I see 250+ engine oil and 245 coolant every time I pull up to the tunnel here from each side when I make my trips to Moab. Just gotta back out of it and find a speed it will hold (usually 50) and chug my way over.
Hope that helps.
CHEERS!
The engine isn't the limiting factor when there's gearing. The same reason old Toyota crawlers ran 37"+ tires no problem with 80hp...and 2 transfer cases. Is it harder to turn a bigger tires? Obviously. Will you likely run in a gear or 2 lower at a given speed with the much bigger tires if you didn't regear your axles? Of course. Is your engine working harder soley because of the tires? Hell no, the biggest reason we get crap mileage in the 1st place is aerodynamics and lifting and going to 40s just took bad aero and made it absolutely atrocious. In city driving when regeared I find I get basically the same fuel economy on 37s as I did on 33s, on the freeway forget about it. It's in the toilet because I'm pushing a lifted brick on big tires at 85mph through a whole bunch of wind.The engine is the limiting factor. It only gives what it has. Gearing helps but it’s still gonna work harder while I’m holding that 20” pipe wrench on the axle instead of the 16” it came with. I get at least 15% better mpg on the Og tires over the 40’s with the same load, or no load for that matter.
Edit:
Some Redneck on YouTube should test the pipe wrench theory while I eat my popcorn.
