Mojave Spring Rate and Bypass Zone

[JET222]

Hello,

I have asked in the past, and just hoping someone that knows finally reads. I am looking to add some bumpers and weight to the Mojave, but I want to keep it in the bypass zone for optimal on/offroad shock absorption. I have been trying to figure out the Mojave coil spring rate and "zone" of optimal shock travel. I wrote Jeep and Fox, and they tell me to talk to the dealership, who tells me they do not know. Basically what I am trying to do is throw a 2.5 inch spring (Clayton?) on the front and rear, but I want to keep it in its optimal zone. Does anyone know or have any way to find out this information? Thanks.

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[KurtP]

Hello,

I have asked in the past, and just hoping someone that knows finally reads. I am looking to add some bumpers and weight to the Mojave, but I want to keep it in the bypass zone for optimal on/offroad shock absorption. I have been trying to figure out the Mojave coil spring rate and "zone" of optimal shock travel. I wrote Jeep and Fox, and they tell me to talk to the dealership, who tells me they do not know. Basically what I am trying to do is throw a 2.5 inch spring (Clayton?) on the front and rear, but I want to keep it in its optimal zone. Does anyone know or have any way to find out this information? Thanks.

I just saw this thread. I dont know the total weight of the mojave spring; but the front will compress 1/4” when adding 160lb on top of the stock bumper

The bypass-zone will function as designed as long as you dont lift the truck above 1” out of neutral

 

[KurtP]

Hello,

I have asked in the past, and just hoping someone that knows finally reads. I am looking to add some bumpers and weight to the Mojave, but I want to keep it in the bypass zone for optimal on/offroad shock absorption. I have been trying to figure out the Mojave coil spring rate and "zone" of optimal shock travel. I wrote Jeep and Fox, and they tell me to talk to the dealership, who tells me they do not know. Basically what I am trying to do is throw a 2.5 inch spring (Clayton?) on the front and rear, but I want to keep it in its optimal zone. Does anyone know or have any way to find out this information? Thanks.

The Rubicon springs are roughly 135 in the front and 180 in the rear; so your fronts will be higher and rears softer. The front 1” lift comes entirely from spring rate, as the free length is the same.

If i was forced to put down a guess on the table; Id guess 145-155 front and 170 rear

 

[unixxx]

@KurtP, any idea why the Mojave has softer rear springs than the Rubicon?

I'm assuming it has firmer fronts to help reduce bottoming out.

 

[KurtP]

@KurtP, any idea why the Mojave has softer rear springs than the Rubicon?

I'm assuming it has firmer fronts to help reduce bottoming out.

Firmer fronts were for bottom out and 1” lift. The free length is the same. Rears were softer for ride/articulation off road at speed.

At least thats what ive been told/measured.

 

[SierraRockCrawler]

Hello,

I have asked in the past, and just hoping someone that knows finally reads. I am looking to add some bumpers and weight to the Mojave, but I want to keep it in the bypass zone for optimal on/offroad shock absorption. I have been trying to figure out the Mojave coil spring rate and "zone" of optimal shock travel. I wrote Jeep and Fox, and they tell me to talk to the dealership, who tells me they do not know. Basically what I am trying to do is throw a 2.5 inch spring (Clayton?) on the front and rear, but I want to keep it in its optimal zone. Does anyone know or have any way to find out this information? Thanks.

Depending on how the 2.5" coil is designed (some manufactures assume additional weight from a winch and aftermarket bumper), you may need to install front shock extensions to keep the front shocks in their optimal range. The Mojave shocks only have about 7.5-8" of total travel, so increasing the ride height by a few inches is significant. I think @KurtP is right about staying within an 1" of stock ride height.

 

[unixxx]

Firmer fronts were for bottom out and 1” lift. The free length is the same. Rears were softer for ride/articulation off road at speed.

At least thats what ive been told/measured.

Not to hijack this thread, but I'm planning to install an RLD cap (175 lb) and Camp King roof top tent (198 lb). With a constant 373 lb load over the bed, I want to swap out the rear springs.

Since the existing spring rate is tuned for the Mojave, I'm thinking it would be best to install longer springs with the same spring rate. However, the 373 lb of extra weight would change the properties of the vehicle, which might actually warrant a higher spring rate to maintain similar handling characteristics.

Any thoughts on whether to go with more length, higher spring rate, or both? In a cursory search, I'm not seeing many technical details online on calculating length and rate.

 

[KurtP]

Not to hijack this thread, but I'm planning to install an RLD cap (175 lb) and Bush Company Alpha roof top tent (238 lb). With a constant 400+ lb load over the bed, I want to swap out the rear springs.

Since the existing spring rate is tuned for the Mojave, I'm thinking it would be best to install longer springs with the same spring rate. However, the 400+ lb of extra weight would change the properties of the vehicle, which might actually warrant a higher spring rate to maintain similar handling characteristics.

Any thoughts on whether to go with more length, higher spring rate, or both? In a cursory search, I'm not seeing many technical details online on calculating length and rate.

Calculating length vs rate vs load can be done but the math is a bit of a pain in the ass and requires a bunch of measurements.

If you plan on lifting the truck, just get a lift spring with a heavier rate like Clayton. If you dont want to lift it, then an airlift spring or a Timbren spring is the way to go, imo, or you could see how a set of max tow springs treat you too.

Ive found there is sufficient rebound damping in the shocks to accommodate my Fabtech springs that compress a little less than an 1”(if memory serves) with about 350-400lb; so you can go up in rate a bit if you want, and max tow springs would probably work well. Just make sure if you lift it you keep the piston within 1” of neutral.

Under a constant load, imo, a heavier spring is the way to go. Other things like airlift or timbren will work, but are better when that load is variable. You could use a spacer to offset some of the sag from the load, but thats not the way to go for a constant load imo.

 

[Needles69]

I just saw this thread. I dont know the total weight of the mojave spring; but the front will compress 1/4” when adding 160lb on top of the stock bumper

The bypass-zone will function as designed as long as you dont lift the truck above 1” out of neutral

I have looked at a lot of bumpers to keep the weight down. So what you are saying is try to keep the total added weight under 160 lbs? The Rugged Ridge Arcus is 70lbs and seems to be the lightest most functional one I have seen at a good price. The mopar bumper is ridiculously overpriced but light if one does not care about spending.

 

[KurtP]

I have looked at a lot of bumpers to keep the weight down. So what you are saying is try to keep the total added weight under 160 lbs? The Rugged Ridge Arcus is 70lbs and seems to be the lightest most functional one I have seen at a good price. The mopar bumper is ridiculously overpriced but light if one does not care about spending.

No, just sayings thats how much my front end compressed with that amount of weight.

I understand different people have different priorities/concerns, but I am personally apprehensive about putting a bumper on my vehicle that hasnt had some sort of crash testing...mopar/ARB/AEV...or at least has a company behind it that can tell me how it was made.

the rugged ridge bumpers looked nice but when i called and emailed to ask questions about the specifics of their steel, how they formed their steel, what testing they had done on their steel, where their steel came from, they either “didnt know” or “wouldnt say” which tells me its all cheap shit that comes from china with zero engineering beyond making it fit ok and look ok.

Specifically to your question, lighter is always better when possible, but i think the truck will drive fine with bumper/winch. If youre blasting through the desert at max effort, youll need more spring. Basically as long as you arent bottoming out the suspension hard all the time and dont have bounce/wallow, you’re good to go.

 

[Needles69]

No, just sayings thats how much my front end compressed with that amount of weight.

I understand different people have different priorities/concerns, but I am personally apprehensive about putting a bumper on my vehicle that hasnt had some sort of crash testing...mopar/ARB/AEV...or at least has a company behind it that can tell me how it was made.

the rugged ridge bumpers looked nice but when i called and emailed to ask questions about the specifics of their steel, how they formed their steel, what testing they had done on their steel, where their steel came from, they either “didnt know” or “wouldnt say” which tells me its all cheap shit that comes from china with zero engineering beyond making it fit ok and look ok.

Specifically to your question, lighter is always better when possible, but i think the truck will drive fine with bumper/winch. If youre blasting through the desert at max effort, youll need more spring. Basically as long as you arent bottoming out the suspension hard all the time and dont have bounce/wallow, you’re good to go.

That is my exact concern. I am preparing for extended trips out west in the desert and don't want to ruin the soft ride nor the intended performance of how the Mojave is designed. As far as the metal its made of it, I am sure its stronger than the plastic/thin gauged metal stock Mopar. The rating is high for usage and I have seen that exact one perform with no issues. The Jeep delarships drop that Mopar winch ready bumper on them all the time for a price of about $1500 No thanks.

 

[KurtP]

That is my exact concern. I am preparing for extended trips out west in the desert and don't want to ruin the soft ride nor the intended performance of how the Mojave is designed. As far as the metal its made of it, I am sure its stronger than the plastic/thin gauged metal stock Mopar. The rating is high for usage and I have seen that exact one perform with no issues. The Jeep delarships drop that Mopar winch ready bumper on them all the time for a price of about $1500 No thanks.

I think it will be fine. Youve got stiffer springs than the stock rubicon up front by a good bit and more travel. If you start getting harsh repeated bottoming, slow down a bit until you dont if saving the suspension long term is your concern.

Youll be able to reach speeds out on the high desert that will over drive the stock setup bumper/winch or not, so just apply common sense and youll have a blast. Might want to consider some better rear bumpstops. I just put the Timbrens in mine and they rock.

 

[NCLife]

Hello,

I have asked in the past, and just hoping someone that knows finally reads. I am looking to add some bumpers and weight to the Mojave, but I want to keep it in the bypass zone for optimal on/offroad shock absorption. I have been trying to figure out the Mojave coil spring rate and "zone" of optimal shock travel. I wrote Jeep and Fox, and they tell me to talk to the dealership, who tells me they do not know. Basically what I am trying to do is throw a 2.5 inch spring (Clayton?) on the front and rear, but I want to keep it in its optimal zone. Does anyone know or have any way to find out this information? Thanks.

What did you wind up doing? I’m considering removing my spacers and swapping in some new longer coils like the Clayton’s you were considering. Rah.

 

[outdoor.adventures]

I uninstalled my Mojave’s Fox 2.5 shocks and took some measurements based on applied pressure on my bench and did some math. Hopefully these are helpful!

Bypass Zones
There are two compression ports and one rebound (extension) port. This is a common setup so that the travel towards bottoming out is dampened in two progressive stages.

• Zone 3: 1 7/8” from full compression
  • Zone 3 is very firm to prevent bottoming out
• Zone 2: 2 7/8” from full compression (1” from Zone 3)
  • Zone 2 is slightly more firm than the ride zone to slow the compression before hitting Zone 3
• Zone 1: 1/4” from full extension (4 3/4” from Zone 2)
  • Zone 1 is to prevent the shock from slamming into full extension
• Ride Zone: this zone is implicit based on Zones 1 and 2 above and lives between 2 7/8” and 7 5/8” of extension - 4 3/4” travel.

Zone Travel
I measured that my Mojave (YMMV) sits level on the ground at 3 1/2” from full extension, or 4 3/8” from full compression. With that in mind, in my opinion these are the most practically useful measurements to determine proper use of the bypass zones with lifts/levels:

• 2 1/2” uptravel from ride height to Zone 3
• 1 1/2” uptravel from ride height to Zone 2
• 3 1/4” downtravel from ride height to Zone 1

 

[unixxx]

@outdoor.adventures, very helpful data. Thanks

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