I have replaced the factory coils on my Jeep Wrangler LJ with an Old Man Emu setup and am wondering if GVW has been increased on a practical level. The springs are certainly much stiffer than the OEM units and I can load more cargo with less sag, but am I kidding myself to think that the GVW is now a bit higher? I am certain that Jeep as the manufacturer would consider it to be the same, but on a practical level can I carry say 15% more weight. Land Rover for instance offers HD springs from the factory that increase the rated GVW. Seems like the same logic would apply here but just not endorsed by Jeep.
Do heavy duty after market suspension coils increase your GVW?
- Thread starter TCM
- Start date
Thanks for your input Dave. From a legal standpoint I agree that exceeding GVW is done at your own risk. Per the law I figure GVW is carved in stone, but from a practical standpoint it it seems reasonable that your load capacity is increased all be it with a negative commiserate impact on braking and frame stress. But the same goes for larger tire sizes and their impact on braking and drive line stress and most of us run larger tires without giving it a second thought. I am willing to assume the legal repercussions of carrying more weight, but am I naive to assume that doing so with heavier springs is not likely to cause mechanical problems if done so in a conservative manner. I am certainly not asking for an unqualified blessing to exceed GWV. I am just hoping to start a dialog as to what the various opinions are regarding this issue.
Troy
Troy
DaveInDenver
Middle Income Semi-Redneck
I think you got it. But I'm not sure everyone thinks about brakes, tires, frame stress, etc. when installing HD springs. What can safely be carried is not just determined by how flat the rear springs might be, but is not trivially impacted by shock valving, stronger /front/ springs, larger caliper pistons & rear drums, C/D/E rated tires and all that other stuff. It's important I think to start the discussion with what GVWR means and what straying beyond it might entail for insurance, lawsuits and the like. I would also be naive in assuming that 100% of us also have considered it when summing up all the armor, camping junk and modifications and all the impact to GVW. I also don't see much discussion about it across all the sub-forums. The heavy camper guys are always talking about, usually with respect to tires, dual/single rear wheels, etc. But for all the 1/2 ton small trucks with loads of steel bolted and welded on, I'd be surprised if most people aren't exceeding their GVW more often than they think. I know my rated limit, base tare weight and loaded total weight and know how all those align or don't... For example, I know that the front springs I run are heavier than most people consider optimal for articulation, but I also know that being heavy in a panic stop situation I need to have a high enough front spring rate to stay in control.TCM said:
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R_Lefebvre
Expedition Leader
Unless you're a licensed professional engineer specializing in vehicle design, your status is unlikely to bear any weight if the unthinkable should happen. That's one of the primary tenets of Professional Engineers. You only have authority in fields which you demonstrate competence.
That being said, none of the OEM engineers doing this stuff are Prof.Engs. The companies only hire degreed engineers, and the company assumes the liability for design faults. Being a personal friend of one of these guys, I can say that you'll never get one to even discuss this issue with you because of liability issues.
One of the biggest factors that hasn't been mentions is axle strength.
That being said, none of the OEM engineers doing this stuff are Prof.Engs. The companies only hire degreed engineers, and the company assumes the liability for design faults. Being a personal friend of one of these guys, I can say that you'll never get one to even discuss this issue with you because of liability issues.
One of the biggest factors that hasn't been mentions is axle strength.
gjackson
FRGS
Land Rover published different GVWs for the Defender depending on what spring package you have. I think the same is true for the 78 series LCs. Have not seen those numbers for anything else though, but the implication is, yes, you can increase GVW with heavier springs. At some point though, other components on the vehicle will become the limiting factor. Without some pretty extensive testing facilities, those GVW numbers would be hard to come by.
cheers
cheers
Crikeymike
Adventurer
Bearings (differential and axle) are a huge factor in what a vehicle can carry. Think about the size difference in proportion of vehicle size (eg. Suzuki Samurai) vs the size bearings it uses, and compare that with a bigger and heavier vehicle. A heavier vehicle design requires a heavier duty bearing design, which is normally just bigger. Wheel bearings wear out in 4x4's quite a bit quicker in my experience when you run bigger tires, because there's more load put on the bearings when you're running that extra width and diameter around a bearing that was designed for a small stock tire. By adding more weight and loading up those bearings, that's where you're likely to have failures, not to mention the brakes.
HD coil springs are designed to hold up the weight of the vehicle with the extra weight that you have put into it, as well as keeping the vehicle's ride height at an appropriate level to maintain ground clearance. If you have a 2" lift with no weight in the back, then you add 400lbs of stuff, you don't want to have a 0" lift all said and done.
I would drop the GVW subject as it doesn't really apply because you can't test all of the components.
Are you or have you exceeded GVW already?
HD coil springs are designed to hold up the weight of the vehicle with the extra weight that you have put into it, as well as keeping the vehicle's ride height at an appropriate level to maintain ground clearance. If you have a 2" lift with no weight in the back, then you add 400lbs of stuff, you don't want to have a 0" lift all said and done.
I would drop the GVW subject as it doesn't really apply because you can't test all of the components.
Are you or have you exceeded GVW already?
Wow this is really a sacred cow isn't it. No I have not exceeded my GVW. I just wanted to get some opinions on the matter as there did not seem to be much discussion regarding the issue here on the forum. The suggestion that I drop it is frankly condescending and altogether unnecessary. I am not asking for anyone to tell me I can carry more weight it just seemed to be a topic worthy of discussion. Crikey!
cruiseroutfit
Well-known member
MoGas said:
I'll do my best but it looks like the basic premise has been covered pretty well.
GVW as noted is a manufacture specification involving countless factors including brakes, suspension, frame, steering and drivetrain. Without an in depth background into the testing and rating criteria from the manufactures one would be un-validated in assuming they have significantly modified their GVWR with a single change (is suspension). I'd suspect each manufacture has their own standard for forming this criteria but its possible an SAE inspired specification (I'll have to dig through my SAE stuff).
You'll note that OME rates some of their heavier spring rate applications (both lead and coil) up to GVW but never would they publish nor advocate an increase in net GVM. Again, its very possible that with suspension upgrades a vehicle GVW has been increased, but without a full in depth analysis replicating the OE criteria, a company would open the door for liability.
On that note, Old Man Emu has some phenomenal engineers (I had a chance to take a class from their suspension guru last month
). They start with a 100% stock vehicle, bench line test the spring rate, dampening, ride quality, suspension travel, etc before they even consider a suspension design for the vehicle. 
Crikeymike
Adventurer
TCM said:
Sorry, it was a poor choice of words. In general it's not discussed because no one really wants to be at or close to GVW.
Crikeymike said:
No worries. I agree that no one wants to be at or near GVW, but I suspect it happens more often than people realize. Who really goes to a weigh station when their truck is fully laden before a trip to confirm the weight. I know I don't, the nearest public scale is almost 25 miles away. I just make an estimate based on what has been loaded into the truck. If it were a bit closer I might make it part of my pre trip routine.
If anyone knows of a truck scale in Boulder, CO please let me know.
Crikeymike
Adventurer
I know that all of the local dumps to here (landfills, places to take your big trash, whatever you call it), they weigh you before you go in, then again when you come out and charge you based on weight. That scale measures you. You could probably just go in there, pull up on the scale, tell the guy why you're there, then turn around and leave.
DaveInDenver
Middle Income Semi-Redneck
I have...TCM said:
Yeah, dunno about a public scale near Boulder. We used to live near a truck stop out in Arvada, but like Mike says, garbage dumps, recycling centers, landscape suppliers, etc. have scales that should work well enough for the purpose. Pretty sure there's a Pioneer Sand in Boulder, I think they have scales.