EcoDiesel GVWR Limiting Factor

[ShadowsPapa]

Let's not forget the load factor of the tires.

True, but even the SL or whatever it's called is 2550 on my General tires. That's a total of over 10,000 pounds, and it's over 5,000 pounds per axle. I figure close to 5,000 pounds for my truck meaning I could add another 5,000 pounds, and if the rear of my truck weighed 2500 pounds, I could load another ton in the back and just be at the max.

But that's maxing everything out and pushing a tire to the very limits - in reality you would be in trouble trying such things with tires.
You do bring up a point too many miss (although I've seen a couple of members mention that they do this) - the sticker PSI on the door jamb is for curb weight of the truck. Load the truck up and you increase the load on the tires and thus need to air them up more. If you normally run 36 and put 1,000 pounds in the back of the truck, you need to increase the psi.

I saw a truck with trailer come into the swap area at the AMO meet in CO last weekend. His tires literally looked half flat and I thought the trailer tires were gonna pop. He never aired up his truck tires for the crazy weight he had (at least 4 complete AMC engines, some transmissions, front suspensions (and I mean complete, cut off the cars) and other stuff.

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[cecaa850]

True, but even the SL or whatever it's called is 2550 on my General tires. That's a total of over 10,000 pounds, and it's over 5,000 pounds per axle. I figure close to 5,000 pounds for my truck meaning I could add another 5,000 pounds, and if the rear of my truck weighed 2500 pounds, I could load another ton in the back and just be at the max.

But that's maxing everything out and pushing a tire to the very limits - in reality you would be in trouble trying such things with tires.
You do bring up a point too many miss (although I've seen a couple of members mention that they do this) - the sticker PSI on the door jamb is for curb weight of the truck. Load the truck up and you increase the load on the tires and thus need to air them up more. If you normally run 36 and put 1,000 pounds in the back of the truck, you need to increase the psi.

I saw a truck with trailer come into the swap area at the AMO meet in CO last weekend. His tires literally looked half flat and I thought the trailer tires were gonna pop. He never aired up his truck tires for the crazy weight he had (at least 4 complete AMC engines, some transmissions, front suspensions (and I mean complete, cut off the cars) and other stuff.

A few weeks ago I loaded my bed with firewood and drove about 45 minutes. Prior to that I put my air pressure half way between the door rating and max psi listed on the tire. On the way home I watched the pressure on the rear tires. The rears went up 2 psi after about 5 miles then stayed there. Pressure increased due to heat. Lower pressure would have generated more heat and can damage tires. Tire pressure is something that people often forget about when loading the vehicle. When we load a pick up here at work with scrap metal we always set the rear tires to max pressure listed on the sidewall.

 

[Schreconjeep]

Ok So I have Cooper STT Pro 37x13.50X17 E Rated tires. I usually keep them around 32psi and air up to 35-37 when I tow my 4k Lb camper with a bed full of stuff. I have heard people running 25psi and 50+psi.... any suggestions? Coming from a cummins 12v and I kept 50psi but this truck is WAY lighter.

 

[ShadowsPapa]

Ok So I have Cooper STT Pro 37x13.50X17 E Rated tires. I usually keep them around 32psi and air up to 35-37 when I tow my 4k Lb camper with a bed full of stuff. I have heard people running 25psi and 50+psi.... any suggestions? Coming from a cummins 12v and I kept 50psi but this truck is WAY lighter.

People who know no better or don't finish reading the whole print on the side of the tire are the ones who inflate to 45 or 50 or more.
That's MAX PRESSURE AT MAX RATED LOAD. Never run a tire at max pressure unless it's carrying a full load for the rating.

 

[FutureOdin]

This is pretty useful, I think: https://www.toyotires.com/media/3729/application_of_load_inflation_tables_20200723.pdf

I went from LT255/75R17 to LT315/70/R17. I was worried about load and bulging since I run them at 33 psi, but if I look at the load rating @ 35 PSI for 315s, its 2535 lbs.

Stock 255s @ 40 PSI is rated for 1965 lbs. So, even at a lower PSI, I should be good--no need to air them up if I'm lugging around equipment/towing.

 

[CrazyCooter]

Ok So I have Cooper STT Pro 37x13.50X17 E Rated tires. I usually keep them around 32psi and air up to 35-37 when I tow my 4k Lb camper with a bed full of stuff. I have heard people running 25psi and 50+psi.... any suggestions? Coming from a cummins 12v and I kept 50psi but this truck is WAY lighter.

I have same tires on 8.5" wheels and have settled on 25psi for daily driving. Seems to be perfect for the front for most daily conditions and allows for a little loading in the rear. I might go up a bit in the rears when towing my travel trailer just for a bit more stability.

Look at the load inflation chart posted above and you will find 25psi is a little high for our weights.

 

[Josh00333]

The diesel engine is a 400 pound add over the gas model.

It's not that much.

Base weight

Sport 3.6 Gas 4691 vs 3.0l D 4972 = 281
Rubi 3.6 gas 5072 vs 3.0l D 5352 = 280

 

[DailyMoparGuy]

No, that's not it - that's just ONE limiting factor. I laid out others - such as the frame, the mounting points of the cab and box to the frame, a whole list of factors. I was only describing how the cooling system factors in to payload and towing.

Agreed. Unless you can get written confirmation from a Jeep engineer on the exact limiting factors, all of this talk is pretty much hearsay. The limiting factor(s) could be one or more of many things.

You don’t wanna be braking hard going down a mountain in the Rockies with 8500lbs of trailer in your backseat because your frame couldn’t handle the stress.

Dramatic I know, but it really irks me when folks don’t just abide by design specs and manufacturer instructions. Human error is the cause the vast majority of accidents, whether automotive, aviation, construction work sites, gun accidents, etc etc.

 

[869 KPH]

You don’t wanna be braking hard going down a mountain in the Rockies with 8500lbs of trailer in your backseat because your frame couldn’t handle the stress.

YUP.

 

[jnack]

The bottom line is that you have a truck, and the GVWR is a recommendation from manufacturer. Jeep doesn't expect you to head to the scales before every camping trip....

I had a Tacoma as my camping rig previously which has a lower GVWR and was often overloaded -- only thing I noticed is the brakes seemed to work harder with heavier loads.

I think your goal should be to keep things as light as possible, but for camping a lot of your extra weight is generally expendable such as fuel, water, food, -- so even if you're a few hundred pounds over at the start of a trip it's not like you're driving around like that everyday. In general, I personally don't fuss too much about it. Maybe if I was going to be driving into the middle of death valley in the summer (why anyone would do that is beyond me)...then i'd make sure I wasn't over the limit, but in general just keep an eye on it and enjoy your truck!

 

[ShadowsPapa]

Recommendation? Uh.........

From an attorney's site - and I think I may have actually found a law on the books at the federal level - more on that later.


What Happens If I Exceed the GVWR?
Exceeding the GVWR is dangerous for several reasons. Manufacturers set this number with safety in mind. Federal regulations back it. If your truck weighs more than it should, there could be severe consequences.

Some of the risks of overloading your vehicle include:

Damaging your vehicle - Brakes and tires are designed with the GVWR in mind. Exceeding the weight limits puts an extra strain on these parts, increasing the chance of a blowout and impacting your ability to stop safely. You can also damage the vehicle’s frame, axles, and other systems.

Being ticketed - If you exceed the weight limit of your vehicle, you could be ticketed. You may find yourself in even deeper trouble if your vehicle’s weight requires you to have a CDL when you don’t.

Causing an accident - Perhaps the most compelling reason to stay within the recommended weight range is to keep yourself and other drivers safe. When you exceed the GVWR, you are increasing the chances you will cause an accident. On top of that, some states consider this action to be criminal. If you are in an accident that causes loss of life, you could face manslaughter charges.

Another interesting tidbit -
SAE J2807 testing includes emergency lane-change and braking maneuvers that replicate situations we encounter in general towing operations. When the engineers finalize all these testing results—and the marketing, service, and legal departments get their say—the tow rating (and load capacity) numbers are published in owner’s manuals and the manufacturer’s online “towing guides.”

Pickup manufacturers take enormous amounts of time to test and evaluate how heavy a trailered load can be towed from both a handling (safety) perspective as well as mechanical, before setting load limits and hitch requirements. They look at every facet of the tow vehicle’s drivetrain, from axles and gears to brakes and transmissions, tested under the most extreme of driving conditions.
Then they test the vehicles in accordance to the specifications in SAE J2807, a comprehensive trailer-towing evaluation program to which all manufacturers now adhere, before setting tow ratings for each make/model truck.

This applies to payload as well as towing, from an attorney's view -
When it comes to negligence or the failure of the driver’s “duty to tow only that which the vehicle is designed to tow,” Dean and other attorneys we spoke with about this issue agree: If there’s an accident and the towing vehicle isn’t properly configured for the trailered weight, the injured person or persons will probably win any ensuing lawsuit.

I found tidbits that indicate there's federal law involved in exceeding ratings, will dig into that and see if it applies to non-commercial or not. Initial indication are that it does because the text I found initially mentions "non-CDL........." and "non-semi-trucks" when talking towing.

 

[Wolf Island Diver]

Resurrecting an old thread….

You can easily increase the practical cargo weight rating of this truck. It’s towing capability already addresses two GVWR issues, cooling and brakes. Folks tend to think of the physical space and the main benefit, but the additional load capability provided by the towing requirement is why the Gladiator is a better overlanding vehicle than a Wrangler. If you’re damaging the frame, you’re doing something dumb, so I’m not going to address this.

The remaining issue you have to deal with and the single biggest limiting system on the truck is the suspension, particularly the spring rate. Unladen, the stock suspension is inadequate. It’s too soft. If you run a lift kit designed to accommodate higher loads and you run bigger tires with a higher load rating, you can easily run heavier cargo loads in the truck beyond its rated capacity. I routinely carry 1200+ pounds of gear and have better handling than the unladen stock truck with less body roll, dive, better cornering, etc. I’ve seen zero effect to brake performance, cooling (even in 90°+ temps) and MPG. The only thing that’s affected mileage on my truck has been tire diameter.

Here’s the key though. I’m robbing Peter to pay Paul. I can carry more gear with no change to braking or cooling but I’m taking away from the effective towing capacity. If you carry more stuff on the truck, you need to tow less or you will begin to exceed the capabilities of the brakes and cooling. If I end up getting an off-road camper next year, I will radically scale back what I carry on the truck. I also just went from 2 1/2 inch AEV springs, to 3 inch springs. They are the exact same length, but the 3 inch springs have far greater load capacity. With the base load of my rack and awning and cargo boxes, I’ve gotten my rake back on the truck moving to 3” springs. And the 2 1/2 inch springs When fully loaded with everything felt too soft to me, still stiffer than stock, but too soft for my liking. It’s really important to get a lift whose height is a function of spring rate not just spring length. And then it’s important for the shocks to work with that spring rate.

 

[ShadowsPapa]

Again gross over-simplification of the ratings and how things work together.
Glad some of these folks don't live and drive around here. First time a deer jumps out or some clown blows a stop sign, you lose control. It's not just springs and tires. Been through all of this before. You increase the height, you increase the center of gravity, etc. Bigger diameter tires also take away from braking. Bigger tires have more leverage over the brakes.
You think you aren't losing out but you are. You absolutely are losing braking performance.
These have to pass certain tests, standards, braking, maneuvering, steering and so on.
To say gee, I can put on different springs and tires and haul more - not really responsible thinking. And to suggest to others it's ok and impacts nothing but towing is even worse.
It's been hashed over ad nauseum over the years.
There's even YT videos out there from responsible 4x4 shops that talk about this.
Zero impact on mpg, now I'm really smiling to myself. No way. It's just not possible to get the SAME mpg with more weight. Drag racers know all about weight, HP, fuel consumption and so on. Sorry, not buying it.

 

[Wolf Island Diver]

Edit: I think I recognize the problem. I’m using the term GVWR. Really what I mean is the load rating which isn’t the same thing. I think you can carry more weight in the JTRD than the ~900 pounds under the right circumstances. That’s not necessarily the same as exceeding the GVWR. Jeeps differences in load/tow and GVWR between configurations is a confusing mess.

Shadow,

Look you’ve seen a lot of stuff I post. Maybe there’s a misunderstanding about just what I’m saying. I have no reason to lie about my mileage. Carrying loads has had a negligible effect on mileage. The only change I’ve seen is going from 33 to 37 inch tires. I went from mileage in the 31 to 33 range on the highway to about 27. I can’t seem to do anything to change my combined mileage from about 23 to 24. I thought adding the awning would affect things. Nope. I thought the Front Runner rack and ROAM boxes would. Nope. When I drive up to the mountains in VA or WV or PA, I lose about 1 MPG on the interstate. This strikes me a pretty typical diesel performance. Terrain, load and towing just done have much of an effect.

I worked as an outside machinist, and then a mechanical engineer on nuclear submarines. I’m well aware of the effect of center of gravity and the moment of inertia of systems. I’ve spent a lot of time doing dynamic analysis of components and systems to determine the performance and survivability. I understand that you can’t just throw “more” at stuff to make it better without deleterious effects. You’re absolutely right that it’s more than just springs and tires. I’m not saying it isn’t.

I’m not making the claim that you can just put heavier springs on anything and it will perform better. This truck has a maximum payload of 1600 pounds in certain configurations and there are a number of factors that reduce that, e.g., the weight of the 3.0L. It’s also true that the truck is designed to tow 6500 pounds which means the cooling system and brakes are designed to handle that. That maximum obviously decreases with the weight of the vehicle and other configurations. Lifted vehicles, have a higher center of gravity. They’re more prone to roll over. There is increased wear on all the parts. Increased loading in the EGR system, etc. All that has to be taken into consideration.

That all being said, it’s been my experience that the stock suspension on my Rubicon ecodiesel is so radically under sprung, and under damped that it verges on dangerous. I’m not the only one who’s observed this. My vehicle would routinely bottom out on the road. Driving home from the dealership when I bought it I had to fight it to keep it in the lane and my vehicle does not have the steering box problem. I’ve never owned a vehicle that drove this poorly, truck or Jeep. I come from a family of auto mechanics, and my father, who’s worked on cars his entire life and has a visceral hatred of modified vehicles rode in this truck and the first thing he said to my shock was “you’ve got to replace the stock suspension on this thing”. When I put a winch on it, oddly enough that had the effect of seeming to dampen the effect of the wandering. However, the truck would bottom out constantly, and then would bounce. It was dangerous.

I’m pretty skeptical of the aftermarket. Most aftermarket stuff is shit. It seems like every lift kit manufacturer claims that their lift improves on road handling. I’m skeptical of that and stiffer isn’t necessarily better. However, in this case, the stock suspension is so bad they are probably right. Personally I’m a fan of AEV, because if you’ve ever talked to Dave Harrinton, the owner, you’ll find that he’s pretty skeptical of the aftermarket and aims for OEM quality. There’s a video of him at SEMA a few years back talking about how bad the stock tuning is. He’s absolutely spot on. They actually have invested millions in testing and advanced manufacturing. This is probably why they are one of the only small aftermarket companies in this market that manufacture OEM parts for GM and FCA.

My experience with my lift is that this completely changed the truck. I don’t mean it made it bad ass. It made it safe to drive. Yes the center of gravity is higher. Yes, the moment of inertia is different. Yes, more weight will have a quantitative affect on braking and load on the cooling system. Yes, it usually will negatively affect emergency handling. If you lift your truck, just like if you tow with your truck and just like if you carry a load in your truck, you should drive accordingly. However, in my experience, the road handling, including the emergency handling, which I have unfortunately had to rely on is vastly improved with this particular lift kit. Even with a full load, the truck handles better than unladen stock. Yes, that’s subjective but I don’t have accelerometers placed all over my vehicle to pull quantitative data. Let me put it this way. It no longer scares the shit out of me when I drive it. When I add up all the gear I’m using it exceeds the original JTRD cargo rating of approximately 900 pounds. I can tell you I would never put 900 pounds in the stock truck. I put 5, 80 pound bags of concrete in the back and it was like driving an old Cadillac with worn out shock absorbers. I don’t need to start solving dynamics problems to know that this lift has improved/increased carrying capacity of this truck in this configuration. That doesn’t mean you can put a lift kit on the configuration that carries 1600 pounds and now carry 2500. The OP taking about the diesel, I am saying there is room to improve this specific configuration’s load rating within limits. And nine months of driving it has borne that out. There is zero chance I would ever own another stock JTRD or maybe any Gladiator. I hear that the other configurations are better, I’d have to get some serious time outside of rose colored lens of a test drive.

With all more weight is there increased risk or decreased margin of safety? Absolutely, just like anybody towing a trailer that isn’t running duellies is rolling the dice that a blowout doesn’t happen, which at highway speeds is likely to lead to a jackknife and roll over. Again, a lifted truck has to be driven differently. A loaded truck has to be driven differently. A lifted and loaded truck absolutely has to be driven differently.

With regards to brakes and cooling what I’m simply saying is the trucks systems are designed for towing and carrying heavy loads. Speaking from my experience after having driven this truck in stock form for nine months on and off road and now post-lift for another nine months on and off road, the cooling system hasn’t had any issues. The braking system consistently works as well as I would expect. I haven’t quantified the delta here between laden an unladen braking performance, but I am very comfortable driving it, including emergency braking. In my experience, with other Jeeps (JK and TJ), when I load the interior with gear, and people, the braking will be sketchy. The truck is designed to tow heavy loads and it has the additional braking and cooling capacity associated with that. If you’re not towing, that additional capacity also improves performance when carrying a load. I don’t think there’s anything even remotely controversial about that.

Lastly, with regards to tires. This is one that particularly bothers me. OEMs put tires on vehicles often with only a passing regard to performance or safety. They choose tires based on cost. Consistently you can find examples from every maker on numerous models where they spec’d a tire that was garbage. You can absolutely positively improve the performance of a vehicle by changing its tires. I have owned multiple vehicles where changing a tire was a difference between something that was sketchy and good performance. Take a Bridgestone and replace it with a Michelin. Take a Firestone and replace it with a GoodYear. you can absolutely achieve better mileage, lower noise, better wet weather handling, better dry weather handling and better towing by changing tires. You can improve the way a vehicle responds to tires. Tire compounds and design directly affect hysteresis. And hysteresis has a profound effect on performance under load.

The stock Falken Wildpeak are garbage. I found the tires to be noisy, they contributed to the wandering, and they had poor wet weather performance and poor loaded performance. FCA chose them for the simple reason that they had the best contract price. They’re also load range C. While it’s not true that switching from a load range C to a load range D tire allows you magically carry more weight. It is absolutely true that if you carry more weight you may have to run a higher load range tire and possible that you will see performance improvements even if you don’t have to. Both tires being mud terrains, with all the singing that entails, my BFG KM3s, which are a load range D, were a shocking improvement on the road from the Falkens. They handle wet weather better, they not more noisy despite being more aggressive and bigger. I also notice that their pressure is more stable as they heat up. I went from 33 inch tires on stock rims to 37s on true beadlock wheels and this combination required probably 1/3 the weight to balance them. It’s shocking just now much weight was on my stock rims. I don’t think these BFGs and AEV rims are that good. I think the stock tires and perhaps the stock rims are just that terrible. So yeah you can improve performance including towing or carrying a load by changing tires. Again, I don’t think that’s very controversial either.

 

[Wolf Island Diver]

My mentioning the beadlocks reminds me of another trope; that beadlocks are inherently dangerous or hard to maintain. Mine have 24 bolts each. I made a pattern template for tightening them, so it takes me about 10 minutes to check the 4 mounted ones. I do this every few weeks unless I’m feeling lazy. I had these wheels about 9 months. So far, after the first month, I haven’t had any bolt back off of its torque at all. That includes checking the spare after rotating it back in, and reinflating it after months of riding under the bed. I’m still trying to understand why these things are such a supposed maintenance nightmare, ticking time bomb or balance issue in people’s minds. Maybe I just got a good set.

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