TJ Shock & Spring Specification Resource Thread

[JMT]

Looking for the 2in lift to run 245/75/17 takeoffs with a front winch and avoid the SYE/track bar/etc changes.

All one can do on the internet is make an educated guess. No one knows how much lift a spring will give your TJ because the sprung weight varies on every TJ (soft top, hardtop, half doors, full doors, rear seat, winch, aftermarket bumpers, spare, no spare, driver weight, the list goes on and on). I can suggest 2933/2942, but hard to know if that will be 2 or 2.5 on your rig.

 

[NOTNSUV]

that's the key. Factory mounts pretty much limit you to around 10-11" of travel at what most consider reasonable lift heights (IMO 4" is as high as it should ever go, and even that is at the very edge of what shortarm geometry and the TJ's hilariously short rear driveshaft works with). Even those running relocated mounts don't end up much past 12" as far as I'm aware. When I hear about 13-14" travels it's usually in the same conversation with coilovers and custom links.

Slight advantage with an LJ's longer driveshaft on limit of lift height?

Unless I change away from RE 4.5" I'm stuck with that or a tad more as measured.

Such a great thread!

 

[freedom_in_4low]

Slight advantage with an LJ's longer driveshaft on limit of lift height?

Unless I change away from RE 4.5" I'm stuck with that or a tad more as measured.

Such a great thread!

For sure in the rear. Though beyond 11" shocks in front, it becomes a game of whether your control arms are so steep that your axle decides its easier to fold backward under the rig than to compress back upward. I'm at 4" lift with 5" uptravel and 6" down, so I could squeeze a couple more inches of ride height out of these shocks if I wanted to...making 6" a hard limit even for a short arm LJ.

But even midarm LJs aren't usually seen with that much lift... Currie and savvy don't even make springs above 4". Usually they're still 4" susp/1.25" body with wide axles, modified fenders and 37+ tires. Somebody that gets into that territory would be more qualified than me to answer why, but I suspect at that point it becomes a tradeoff of CoG vs diminishing returns of more belly clearance.

 

[jjvw]

For sure in the rear. Though beyond 11" shocks in front, it becomes a game of whether your control arms are so steep that your axle decides its easier to fold backward under the rig than to compress back upward. I'm at 4" lift with 5" uptravel and 6" down, so I could squeeze a couple more inches of ride height out of these shocks if I wanted to...making 6" a hard limit even for a short arm LJ.

But even midarm LJs aren't usually seen with that much lift... Currie and savvy don't even make springs above 4". Usually they're still 4" susp/1.25" body with wide axles, modified fenders and 37+ tires. Somebody that gets into that territory would be more qualified than me to answer why, but I suspect at that point it becomes a tradeoff of CoG vs diminishing returns of more belly clearance.

Arm length doesn't affect the amount of travel we can get on a TJ or LJ. I've outboarded rear 12s on both short and mid and converted an existing outboarded short arm to a mid. The practical limits become ones of packaging the shock, as well as axle width with reasonable wheel backspacing. That is why 11s tend to be where we stop on the front. Squeezing a 12 in there is nowhere near as easy as the rear is.

Rubicons get driveshaft bind at droop with high skids and 4" lifts. But that can be addressed with a center limit strap.

Most people don't put themselves into situations where control arm jacking matters. But that is one of the primary reasons to put longer arms up front.

 

[NOTNSUV]

Rubicons get driveshaft bind at droop with high skids and 4" lifts. But that can be addressed with a center limit strap.

High skids meaning tummy tuck?

Gonna have to look at/for "center limit strap" now. Sounds simple enough.

 

[jjvw]

High skids meaning tummy tuck?

Gonna have to look at/for "center limit strap" now. Sounds simple enough.

Hang the suspension from the shocks first and try bolting the driveshaft onto the pinion twice after a 90deg turn before solving a problem you might not have.

 

[NOTNSUV]

Yeah, I meant research how to find out if it's an issue and what might be done if it is, since I never heard of it. Makes sense it could happen, but probably not real common.

 

[jjvw]

Yeah, I meant research how to find out if it's an issue and what might be done if it is, since I never heard of it. Makes sense it could happen, but probably not real common.

It's a problem with short driveshafts. The TJ Rubicon happens to have one of those.

 

[freedom_in_4low]

Arm length doesn't affect the amount of travel we can get on a TJ or LJ. I've outboarded rear 12s on both short and mid and converted an existing outboarded short arm to a mid. The practical limits become ones of packaging the shock, as well as axle width with reasonable wheel backspacing. That is why 11s tend to be where we stop on the front. Squeezing a 12 in there is nowhere near as easy as the rear is.

Rubicons get driveshaft bind at droop with high skids and 4" lifts. But that can be addressed with a center limit strap.

Most people don't put themselves into situations where control arm jacking matters. But that is one of the primary reasons to put longer arms up front.

I didn't mean into imply that it was, I was mainly just musing on why we don't see many quality suspension lifts over 4". And I agree the arm length doesn't limit travel, but I do think it places bounds around practical lift height due to things like instant center/antisquat, clearance issues vs loss of wheelbase arising from the arc of the rear axle, etc.

Gotta be careful though, don't want to turn this into another geometry correction thread.

 

[jjvw]

I didn't mean into imply that it was, I was mainly just musing on why we don't see many quality suspension lifts over 4". And I agree the arm length doesn't limit travel, but I do think it places bounds around practical lift height due to things like instant center/antisquat, clearance issues vs loss of wheelbase arising from the arc of the rear axle, etc.

Gotta be careful though, don't want to turn this into another geometry correction thread.

All of that together and more adds up to why ~4" is the practical limit on stock axles and stock wheelbase. Skyjacker doesn't care, though.

 

[Irun]

Skyjacker doesn't care, though.

It's clear that many don't care!

 

[UKTJ]

Looking at the quoted free lengths and spring rates of the OME 941 and 942 rear springs is very confusing, to me at least.

The 941 has a free length of 15.53" and a spring rate of 140lbs. The 942 has a free length of 14.96" and a spring rate of 160lbs. Based on those figures with an sprung load per spring of 650lbs each spring yields a compressed spring height of:
941 = 10.89"
942 = 10.90"
Increase that load per spring to 750lbs and you get:
941 = 10.17"
942 = 10.27"
Increase that load per spring even more to 850lbs and you get:
941 = 9.46"
942 = 9.65"
Indeed, if you want to get to a 1/2" difference in the springs the load needs to be at 1200lbs per spring:
941 = 6.96"
942 = 7.46"
At which point the Jeep is lower than stock.

In short, at any reasonable sprung load per corner, the additional length of the 941 seems to almost completely compensate for the higher spring rate of the 942. If the table is showing correct values then what is the point of the two different springs and how should somebody choose between them?

 

[freedom_in_4low]

Looking at the quoted free lengths and spring rates of the OME 941 and 942 rear springs is very confusing, to me at least.

The 941 has a free length of 15.53" and a spring rate of 140lbs. The 942 has a free length of 14.96" and a spring rate of 160lbs. Based on those figures with an sprung load per spring of 650lbs each spring yields a compressed spring height of:
941 = 10.89"
942 = 10.90"
Increase that load per spring to 750lbs and you get:
941 = 10.17"
942 = 10.27"
Increase that load per spring even more to 850lbs and you get:
941 = 9.46"
942 = 9.65"
Indeed, if you want to get to a 1/2" difference in the springs the load needs to be at 1200lbs per spring:
941 = 6.96"
942 = 7.46"
At which point the Jeep is lower than stock.

In short, at any reasonable sprung load per corner, the additional length of the 941 seems to almost completely compensate for the higher spring rate of the 942. If the table is showing correct values then what is the point of the two different springs and how should somebody choose between them?

There are TJs that come in close to 1200 per corner with lots of steel armor, tools, and gear.

There probably aren't many TJs with only 850 per corner. Maybe an SE with no top or doors and no aftermarket anything.

Most are probably around 1000.

 

[UKTJ]

There are TJs that come in close to 1200 per corner with lots of steel armor, tools, and gear.

There probably aren't many TJs with only 850 per corner. Maybe an SE with no top or doors and no aftermarket anything.

Most are probably around 1000.

Heck, that is an awful lot of sprung weight. If that is the sprung weight, how much do those TJs weigh in at in total? With 1200lbs sprung weight in the rear corners the figures quoted on page 1 for the Skyjacker 6" lift spring would only yield about a 3" lift, so what springs are these people using to run 35s or bigger?!? Are you sure you are referring to sprung weight?

But that aside, for a TJ of those epic proportions the point is both of these springs would be useless anyway, as they would be giving negative lift versus a stock TJ anyway. That is my point, in the useable range, based on the figures quoted on page 1 they seem to yield essentially the same result. That is not the case for the equivalent front springs.

 

[jjvw]

There are TJs that come in close to 1200 per corner with lots of steel armor, tools, and gear.

There probably aren't many TJs with only 850 per corner. Maybe an SE with no top or doors and no aftermarket anything.

Most are probably around 1000.

1200lbs sprung weight per corner is oppressively heavy even for an over loaded TJ.

 

[jjvw]

....

In short, at any reasonable sprung load per corner, the additional length of the 941 seems to almost completely compensate for the higher spring rate of the 942. If the table is showing correct values then what is the point of the two different springs and how should somebody choose between them?

In short, these are sprung weight scenarios that lean towards the excessive side.

 

[UKTJ]

In short, these are sprung weight scenarios that lean towards the excessive side.

Sorry jjvw, which weights lean towards excessive? The ones in my first post on this? I started at 650lbs per rear corner, is that still high?

 

[freedom_in_4low]

1200lbs sprung weight per corner is oppressively heavy even for an over loaded TJ.

That's true. I was just thinking back to seeing some 4800 pounders in the weight threads and didn't think about taking unsprung weight out of the equation.

On a typical 30/44 TJ, that's probably what, 200 ish per corner? So the OP is onto something with there not being much of a difference in the two springs in question.

 

[jjvw]

That's true. I was just thinking back to seeing some 4800 pounders in the weight threads and didn't think about taking unsprung weight out of the equation.

On a typical 30/44 TJ, that's probably what, 200 ish per corner? So the OP is onto something with there not being much of a difference in the two springs in question.

Mine is about 4600lbs overall with a rear corner weight no more than 950lbs.

 

[jjvw]

Sorry jjvw, which weights lean towards excessive? The ones in my first post on this? I started at 650lbs per rear corner, is that still high?

1200lbs is pretty high.