Rubi springs change tow?

[Gren71]

Ive been searching the forum and there are a TON of threads that talk about it. But it seems mostly anecdotal bro science and, as far as I can find, there hasnt been a consensus on if the rubi springs will lower the tow capacity of the max tow jt.

does anyone know definitively?

i know i could keep reading the plethora of threads with info. But theres too many, and i frankly cant devote that kind of time to reading every word.

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[Oscar Indy]

Springs have very little to do with tow capacity. The difference between the Rubi and MaxTow is primarily in tire size. Equipment wise for towing is the only real difference between the MaxTow and Rubicons.

As far as springs go they are very different and that's why one has a higher payload than the other.

Physical the Rubi spring is a 7 coil vs the max is an 8 coil.
For what it's worth this explanation came form the product manager at Jeep when I asked him about springs and packages.

 

[Gren71]

Springs have very little to do with tow capacity. The difference between the Rubi and MaxTow is primarily in tire size. Equipment wise for towing is the only real difference between the MaxTow and Rubicons.

As far as springs go they are very different and that's why one has a higher payload than the other.

Physical the Rubi spring is a 7 coil vs the max is an 8 coil.
For what it's worth this explanation came form the product manager at Jeep when I asked him about springs and packages.

thanks for the prompt reply! Sounds definitive to me.

 

[bgenlvtex]

Irrespective of springing the difference in tow capacities is directly related to the weight of the Rubicon.

 

[ShadowsPapa]

I have a pair of Rubicon rear springs - one is shorter and has 9 coils, the other is a tad longer and has 8.
They are number 449 and 450.
The shorter 449 spring has 1 more coil than the 450.
They are similar in length to the max tow springs I have sitting here.
Some Rubicons get 450/451 rear coils. Likely depends on options, weight of the vehicle as built.

The max tow has progressive rate springs - meaning they'll handle the weight of the payload and expected increased tongue weight better.
As far as pulling or towing - no change.

By the numbers - the 7,650 max tow tow rating vs the 7,000 pound tow rating of the Rubicon is only 650 pounds difference.
If you figure typical tongue weight of 10% of the total trailer weight, that's a difference of 65 pounds tongue weight.
I don't think I'd worry about that.

The extra weight of the Rubicon is likely one reason for that difference, because they must factor in the tongue weight of the thing being towed when they rate for towing - can it handle the weight of the tongue.
Even if they can pull the same thing, they have to figure the weight of the tongue as being "payload" on the back end.
So you are talking a whopping 65 pounds difference tongue weight.

If it was me - I'd not worry about it towing anything less with Rubicon springs, I might wonder about how the rear end sits with the trailer hooked up - but that can be handled in multiple ways if it does change in a negative way in YOUR case.
A. Put the springs under it - give it a try, if it sits too low with your trailer - switch back
or
B. Put them under and if it sits low - use air bags or some other means to level it back out.
But I'd not worry about it towing any less.

 

[ShadowsPapa]

Curb weight with manual transmission (I believe you add something like 25 pounds to each to get the curb weight of each with automatic transmission)

Curb Weights:
Rubicon 5050 lbs.
Sport 4650 lbs.
Overland 4720 lbs.

Sport is 400 pounds lighter than Rubicon.
Sport is 70 pounds lighter than Overland.
Overland is 330 pounds lighter than Rubicon.

 

[Oscar Indy]

Curb weight with manual transmission (I believe you add something like 25 pounds to each to get the curb weight of each with automatic transmission)

Curb Weights:
Rubicon 5050 lbs.
Sport 4650 lbs.
Overland 4720 lbs.

Sport is 400 pounds lighter than Rubicon.
Sport is 70 pounds lighter than Overland.
Overland is 330 pounds lighter than Rubicon.

Don't forget the MaxTow sport uses same axles and everything but the TCase that the Rubicon has. That makes it heavier than a sport.

360lb difference is two tiny occupants.
On the other side the tire size difference makes about 200rpm difference in all gears.

 

[ShadowsPapa]

Right - I was merely pointing out the base weights of each without towing (and in a way how they aren't huge differences) - add the wider axles to the Sport and you add weight to it, reducing the difference.
That will impact payload more than towing in either case.

Bottom line - springs will have an impact on how it sits with weight in it, and tongue weight, not how hard it can pull.
I'd not worry about losing pulling ability with springs.

But on the other hand - WHICH Rubicon springs?
There are multiple choices here. There are heavier duty springs, lighter duty springs, and those in between.
The Rubicon with a tow package and all decked out with all options will have the higher numbered, and thus, heavier, springs, while a Rubicon with fewer options will have lighter springs, and a Rubicon without the tow package would have the lightest springs of all Rubicon.
You can't just say "Rubicon springs" any more than you can say "Overland springs" or "Sport Springs".
I personally know of these -
An Overland with 440 and 441 rear coils even with the towing package - but mine has 439 (left) and 440 (right) with the towing package. So mine has lighter rear springs than another for some reason.
A Rubicon with 450 and 451 rear coils yet I have a Rubicon set with 449 and 450 rears which are lighter springs.

 

[WXman]

With all due respect, that chart above has errors in it. For example, how can you get a Sport with 4.10 gears and 1,100 lbs. payload? Not possible. And one error spoils the entire jar. Can't trust it.

I also disagree that the tires have that much to do with it. Sport and Overland both use the same diameter tires, but towing specs are all over the map due to curb weights and other concerns. Has nothing to do with tires.

300-400 lbs. of curb weight has a lot to do with it. My Max Tow was 4,700 on the scales when it was stock. I've seen stock Rubicons pushing 5,100.

The coil springs have a lot to do with it also. More spring rate = better payload = better tongue weight = better towing.

 

[ShadowsPapa]

With all due respect, that chart above has errors in it. For example, how can you get a Sport with 4.10 gears and 1,100 lbs. payload? Not possible. And one error spoils the entire jar. Can't trust it.

I also disagree that the tires have that much to do with it. Sport and Overland both use the same diameter tires, but towing specs are all over the map due to curb weights and other concerns. Has nothing to do with tires.

300-400 lbs. of curb weight has a lot to do with it. My Max Tow was 4,700 on the scales when it was stock. I've seen stock Rubicons pushing 5,100.

The coil springs have a lot to do with it also. More spring rate = better payload = better tongue weight = better towing.

We know the chart was wrong just on the fact it stated they calculated in a driver. No one does that, even the owner manual states otherwise. Towing sites all differ as well.
In any case, towing ability is a system. It's not just one part. One part may impact it more or less than another part, but you can't add a part and make it max tow, and you can't take away one part and make it the same as some other model either.
Jeep worked hard to find the right COMBINATION of factors - gear ratios, cooling capacity, springs, spring rates, vehicle weights and more.

Something that's been bugging me all along - why would someone take max tow springs out to install Rubicon springs?
Me - I'd be wanting to put in max tow springs - oh, wait, I plan on doing just that to handle the tongue weight better.
I guess that's my question - why? Why downgrade rear springs with Rubicon springs?
You WILL lose some payload capacity, you will drop more with weight in the back, you will drop a bit more with tongue weight on it.
How much - we don't know because we don't know WHICH Rubicon springs are planned - there are several combinations of Rubicon springs to choose from. Like I posted above - when one says "Rubicon springs" - I'd ask - which ones?

 

[Gren71]

Something that's been bugging me all along - why would someone take max tow springs out to install Rubicon springs?

a lot of non rubi owners get them for the added 1in of lift provided with out having to pay the $1,800 ( or what ever it is) for the mopar lift.

Ill probably just go with the daystar 2in spacer kit, but i twas curious.

 

[ShadowsPapa]

a lot of non rubi owners get them for the added 1in of lift provided with out having to pay the $1,800 ( or what ever it is) for the mopar lift.

Ill probably just go with the daystar 2in spacer kit, but i twas curious.

Ah, ok. Two people here who have swapped and put in "Rubicon springs" both reported about 3/4" difference when done.
But I don't know WHICH number springs they used - could have been the 449 and 450 rears and 339 and 340 fronts or heaver 450/451 rear coils. Dunno.
Also don't know how much difference it would make using the 449/450 combo in the rear vs 450/451 combo.
Would the higher number, thus slightly stiffer springs make it more than 3/4" or is that the combination that gave them the 3/4" difference talked about?
Since you are talking a 3/4" difference - and potential payload difference with the other springs, IF IT WAS ME - my opinion, for every penny of value that you paid for it (money back guarantee and all) - I'd opt for a spacer lift.

 

[PyrPatriot]

a lot of non rubi owners get them for the added 1in of lift provided with out having to pay the $1,800 ( or what ever it is) for the mopar lift.

Ill probably just go with the daystar 2in spacer kit, but i twas curious.

Right, it makes sense for a base sport or overland model. But you already paid more for the Max Tow package to give you better payload, why downgrade the payload with the Rubicon springs?

 

[PyrPatriot]

Ah, ok. Two people here who have swapped and put in "Rubicon springs" both reported about 3/4" difference when done.
But I don't know WHICH number springs they used - could have been the 449 and 450 rears and 339 and 340 fronts or heaver 450/451 rear coils. Dunno.
Also don't know how much difference it would make using the 449/450 combo in the rear vs 450/451 combo.
Would the higher number, thus slightly stiffer springs make it more than 3/4" or is that the combination that gave them the 3/4" difference talked about?
Since you are talking a 3/4" difference - and potential payload difference with the other springs, IF IT WAS ME - my opinion, for every penny of value that you paid for it (money back guarantee and all) - I'd opt for a spacer lift.

If payload was more important than towing capability, I'd just put on bigger tires and a spacer lift, as that preserves that outstanding 1500lb payload. If towing was more important, I'd leave stock because anything done to the JT Max Tow will decrease it's towing capacity. If I want both to remain the same because that's what I bought the Jeep for, I'd have it in stock configuration for towing and larger tires for when I don't need to tow.

Now I wonder how does the Mopar lift kit affect the payload capacity? I'm sure Jeep intended Rubicon's to get the lift in many if not most cases. Rubicons already are at 1100-1200lbs of payload compared to the Sports 1500-1700lbs. I'm sending FCA an email asking how their lift kits affect payload, as the springs are different.

 

[ShadowsPapa]

Rubicon is 400 pounds heavier than Sport S and gives up 650 pounds in tow rating making curb weight change slightly more than 60% of the tow reduction.
Pretending that is insignificant is just that, pretend.

All of which is really moot, because you aren't going to tow @ max for any appreciable difference with either one.

We know weight is a lot to do with it because look at the GCWR - that is the weight of the vehicle AND trailer.
So the lighter the vehicle, the more trailer it can handle if all else were equal. The Rubicon being heavier means it can't tow as much if the rest is the same (engine, transmission, gear ratio, etc.)
The fact that the Sport S is xxx pounds lighter means it can tow that much more if all else is the same - and frankly, with the engine, transmission, gear ratio, cooling system and all else being the same - there's a chunk of the difference between the 7,000 of the Rubicon and the 7650 of the Sport S.


GVWR vs GCWR
GVWR refers to weight capacity of the vehicle alone. (Vehicle plus people plus stuff you toss into the vehicle)
GCWR, however, is a weight rating of the vehicle but takes a hitched up trailer into account. It is the maximum weight of a vehicle with a trailer attached.

So if the tow vehicle was 1,000 pounds heavier but ALL ELSE WAS THE SAME, then the heavier vehicle would be labeled to tow 1,000 pounds less.
Springs are more for payload and tongue weight to put it in simple terms. Heavier trailer, means heavier TONGUE, more weight on the tow vehicle, GENERAL, generic rule - 10% of the total trailer weight as tongue weight. So a 3,000 pound trailer means 300 pounds tongue weight. That's where springs come in - holding the weight up, preventing sag, and helping with stability. Saggy or weak springs means an unstable tow vehicle under load.
So springs do matter there. Wimpy springs, not a great experience in the truck. A lot of wobble and wiggle and sway.

Tires - if it's tire diameter, well, the automatic will be in whatever gear is needed to give the engine an advantage. For the Silverado, the difference was the differential ratios, all else being the same. In this case, we have two models with 4.10 ratios so that's out the door.
We're talking the Falken A/T tires with a diameter of 32.8" (not really 33 from the sites I've looked at). The difference in rotations between those and the tires on my Overland is a whopping, what, dozen, maybe 2 dozen, revolutions per mile?
Anyone want to look up the tire size differences according to the tire MAKERS, and figure the differences in revolutions per mile? With 8 speeds I'd expect the transmission to shift to and stick with whatever it needed to in order to handle the load at hand.

Anyway, it's a system - all parts have to work together. Springs, gear ratio, vehicle weight, all of it.

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