Cooling, most likely.
They didn't upgrade the cooling on the mojave though, magic 1k pound increase or proof that the rating are overly conservative?
I mean the grill. It was changes for more air flow.
I don't know about absolute certainty put the Mojave frame was already strengthened over the Rubicon and max tow to start with according to Jeep so why would it be the weak link? If the grill made the difference tab went didn't the Rubicon or max tow go up? We can pretend something changed, which is technically true as the rating went up by 1k pounds.
Definitely a complex topic, but the max tow, Rubicon, and mojave are all pretty equal in every aspect that matters. The rubicon and mojave even have the same sized tires. There's no logical reason they weren't rated the same, and with no changes they now are. That tells the whole story as far as I'm concerned. And if we are saying the cooling system is the limiting factor not pulling grades in 90⁰+ weather would further increase capability since that's how they were certified.
I've found the stock springs on every Jeep too soft. Same with the stock shocks even on a Rubicon. The mojave is the only factory shock that feels like it's adequate for even stock tires. Every lift spring is firmer and so is every aftermarket shock. For all of those reasons I'm not sure you'd see as much difference as you think after a lift. Yes the cog is higher and tires are larger but dampening and sway control are often improved over stock in my experience. The larger tires will increase braking distance for sure, but short of testing or at least knowing how close the stock setup was to the 80' limit I wouldn't assume it would fail that test after a lift and tires. I'm not certain it would fail any of them for that matter having towed heavy with my lifted truck. Add in the other mods and in my opinion it handles better and is more stable than it was stock empty.We are also leaving out the other factors, suspension/shocks, etc.
They test for understeer and so on - so a softer suspension can be problematic. The Rubicon suspension is different and likely to change the results of the SAE testing.
Minimum temperature of 100 degrees at the base of the grade.
Subtract the total weight of the tow vehicle (the TVTW includes the weight of the driver, passenger, and additional equipment) from the tested GCWR, the result is the SAE J2807-compliant Tow Weight Rating.
Braking matters - TIRES matter -
The J2807 standards also have requirements for the braking performance of the truck-and-trailer combination at its maximum GCWR. Combos with a maximum tow rating of more than 3,000 pounds are required to stop completely from 20 mph in 80 feet or less. During this stop test, the trailer must remain within an 11.5-foot-wide lane throughout the entire stop. In addition to the active testing, the parking brake must be able to hold the truck and trailer firmly in place both upward and downward on a 12 percent grade when it is at the maximum GCWR.
Suspension - weight shifting to the front, understeer, softer suspension might be problematic -
The truck-and-trailer “Combination Handling Requirements” of J2807 specify minimum performance for understeer and trailer sway response. The tests are designed to determine the limits of the weight carrying, weight distributing, and stability of a fifth-wheel/gooseneck trailer, with the combo at its maximum GCWR. Understeer (the opposite of fishtailing) is measured at three different levels of Front Axle Load Restoration (FALR), which is a calculation of how much the load on the front axle changes.
The test criteria doc is over 2 dozen pages.
A few of the tests -
Lifts and bigger tires are really going to screw with much of that, especially the STOPPING and understeer testing, sway test and such because so much has changed about the vehicle.
And ratings aren't either. They are suggestions at most.
Again you're assuming the testing took the vehicle to any one of those limits? Like they are just out there for weeks adding weight until it fails one of the tests. The mojave gaining 1k pounds of capacity without any changes disproves that. The manufacturer picks the weight they want it certified for and runs all the tests. Pass them all and your certified and done. Would a max tow pass at 8k? Maybe. Did they test it at 8k? Maybe. If it failed where did it fail? We will never have all the info to say one way or the other.
So far yes you’re half right, only the payload rating is actually on the sticker. However as the driver it’s your duty and responsibility to not be ignorant about your vehicle and what it’s capable of. Hey you want to go out there and create a hazard for all the folks around you? That’s not right. Also that ignorance will provide the grounds for your insurance company to drop you, leaving you out to live with a huge financial mess. Good luck.
