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Discussion Starter · #1 ·
2009 JK 2-door

I Recently had my axles built (trussed etc) and re-geared to 4.88. Just before the axle build I took her from 2.5” metalcloak springs to 3.5” rock crawler springs and installed a steering flip kit. Lastly I moved from 35” e rated Nittos to 37” d rated Patagonias.

I’ve noticed that the Jeep now doesn’t feel very stable on the road - like if I had to swerve to miss something I’d probably roll over. I’m okay with that if it’s just how a 2-door is gonna feel once built like this, but I just want to make sure I’m not missing anything that might be THE factor.

Unfortunately I changed too many things at once so now I don’t know which factor might be the main culprit... but I’m under the impression that I didn’t feel this instability until I added the Patagonias. I could be wrong - it might just be that I didn’t really notice it till then. They are 2” taller than the tire I had before so maybe that’s just a little bit more raise in CG than the Jeep can take? They are also D instead of E rated so maybe a stiffer sidewall would add stability?

I’d love to hear from anyone with a similar setup re the on-road stability of your rig and whether this is just how it’s gonna be or are there measures I could take to regain stability without taking everything back down.

Here she is...



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2009 JK 2-door

I Recently had my axles built (trussed etc) and re-geared to 4.88. Just before the axle build I took her from 2.5” metalcloak springs to 3.5” rock crawler springs and installed a steering flip kit. Lastly I moved from 35” e rated Nittos to 37” d rated Patagonias.

I’ve noticed that the Jeep now doesn’t feel very stable on the road - like if I had to swerve to miss something I’d probably roll over. I’m okay with that if it’s just how a 2-door is gonna feel once built like this, but I just want to make sure I’m not missing anything that might be THE factor.

Unfortunately I changed too many things at once so now I don’t know which factor might be the main culprit... but I’m under the impression that I didn’t feel this instability until I added the Patagonias. I could be wrong - it might just be that I didn’t really notice it till then. They are 2” taller than the tire I had before so maybe that’s just a little bit more raise in CG than the Jeep can take? They are also D instead of E rated so maybe a stiffer sidewall would add stability?

I’d love to hear from anyone with a similar setup re the on-road stability of your rig and whether this is just how it’s gonna be or are there measures I could take to regain stability without taking everything back down.

Here she is...



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Did you upgrade the front lower control arms to fix the caster?

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Discussion Starter · #3 ·
Did you upgrade the front lower control arms to fix the caster?

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Yeah sorry - shoulda gone into all of that. Yes - have adjusted the MC control arms and everything else to get the geometry set up. I don’t see any really potential for anything to be wrong there. Most of it was installed by me but I had the guy who welded the axles for me go over everything and make any needed adjustments. He’s a pro and everything there is solid.




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Discussion Starter · #4 ·
Unless I’m missing something I’m guessing that what it’s going to boil down to is...

37s on 3.5” are just gonna feel that way

Or

Something tire related (I should have gone with a stiffer sidewall (E) or a wider tire )


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Spring rates probably changed between the two different coils which could make a big difference. Shocks may be not be a good match to the springs. Stiffer sway bar might help.
 

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What about your rear trackbar? Did you get an adjustable to align the axle right to left? Then there is the trackbar height. Did you get either an axle side or frame side trackbar bracket to make the trackbar more parallel to the axle. At 3.5” lift you will need this to reduce your roll center.
 

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Discussion Starter · #7 ·
Spring rates probably changed between the two different coils which could make a big difference. Shocks may be not be a good match to the springs. Stiffer sway bar might help.


I’ll look at that. Am running the Fox 2.0s with reservoir now.


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Discussion Starter · #8 ·
What about your rear trackbar? Did you get an adjustable to align the axle right to left? Then there is the trackbar height. Did you get either an axle side or frame side trackbar bracket to make the trackbar more parallel to the axle. At 3.5” lift you will need this to reduce your roll center.


Yup - adjustable track bar is in place. Did that long ago - I think it was Terraflex. Don’t recall on the raised bracket though - will check


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Have you had it on an alignment rack to see what your numbers are?
 

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I have a rock krawler 3.5 lift and 37’s on my JKU and experience none of your issues.

When the lift was first installed it didn’t behave how I expected. A alignment and proper PSI in the tires corrected those issues. Behaves better the factory now.

As others stated alignment & correct PSI in the tires is where I would look first. I am far from a mechanic, however those were the two areas that corrected my issues
 

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Lot's of sound insights on this thread. As @NC25T indicated, a raised JK on 37"s may not challenge a Corvette through the turns, but it should still be ok.

What tire pressure are you using? Which Nittos are you coming from (assuming Patagonia M/T)?

The step after that is to take a few hours and measure everything. String the car. check caster. Check all the fasteners on the suspension and steering. Check the wheel bearings. Make sure all the springs are fully seated. Most of this stuff has already been mentioned, but doing it all together often finds stuff missed earlier. The equivalent of a code review.

Did you measure the actual lift height front and rear, left and right, before and after? Is it really 1" or maybe more? Are those all JK springs or are they JKU springs by accident?
 

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There is really a lot of things people have mentioned (including your own thoughts) that could all contribute to the increased instability you are describing. I would suggest that it isn't just one but a combination of things causing it. Part of the question you will have to feel out is it it truly dangerous or just feels different enough that it concerns you.

Here are my thoughts.

For one the 37" Pats are definitely going to add a little sponginess to the ride vs the e rated 35" tires you were running before. Sidewall stiffness from a slightly smaller, 10 ply e rated tire is going to make a big difference. You probably feel that the Pats absorb alot more of the small square edged bumps and smooth out the ride but at the same time, they are most definitely going to give you more sidewall flex and roll in the corners. I suggest playing with the air pressure a bit and see if it will help the situation at all.

You went from a dual stage 2.5" MC coil to a 3 stage 3.5" RK coil. So, not only have you already raised your center of gravity up slightly with a larger (and softer) tire but you have now added an inch or more lift with the RK coils. The additional height alone will have some effect but so won't the design of the springs. The 2 stage MC coil acts like a single stage coil when driving around with the added benefit of a second stage that will extend to keep the spring seated when the suspension droops out. The RK coil is 3 stage. So it has a soft section of coil for when you are driving around, a stiff section of coil that comes into play when you compress the spring to help the suspension from bottoming and a 3rd stage of coil that is normally collapsed fully under the weight of the Jeep and only extends to keep the spring seated when the suspension is drooped out. This first/soft stage is probably allowing a little more floating that you have been accustomed too.

I'm going to mention here real quick... Did you, or have you, adjusted/replaced your sway bar links? If they are too short the sway bar doesn't have all its mechanical advantage it is supposed to have and therefore not the control over body sway/roll.

Shocks... I have found the Fox reservoirs to be a little soft. I have also driven some very stiff custom valved Fox shocks as well. Maybe it's worth having them re-valved to get a little more control over the suspension. For example I have RC coils, 38" C-rated Pats, and Antirock sway bars. My Jeep should be a mess! It's not... Why? Falcon 3.3 shocks. Even at the softer settings they are a fairly stiff shock. They work wonders at keeping my Jeep feeling almost sporty... Please don't think I mean like a Corvette.. I'm not crazy!

Then there are things like Caster? What is it at currently? You want 5.5 degrees or as close as you can get. If caster is too low it will get very darty/twitchy feeling. This can scare the crap out of you at highway speeds. It will feel like it would rather change lanes than go straight. White knuckle ride for sure!
With 3.5" of lift I am assuming you have a raised track bar mount? If not you will need to to get your roll center back. And if you did, did you flip the drag link as well? If not you will experience a ton of bump steer.

There are so many things that could be going on so take your time and eliminate what you can. There are a lot of similar builds on the roads that do drive perfectly fine so don't give up if your not satisfied. There are combinations of parts out there that will get you sorted out.
 

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Discussion Starter · #14 ·
There is really a lot of things people have mentioned (including your own thoughts) that could all contribute to the increased instability you are describing. I would suggest that it isn't just one but a combination of things causing it. Part of the question you will have to feel out is it it truly dangerous or just feels different enough that it concerns you.

Here are my thoughts.

For one the 37" Pats are definitely going to add a little sponginess to the ride vs the e rated 35" tires you were running before. Sidewall stiffness from a slightly smaller, 10 ply e rated tire is going to make a big difference. You probably feel that the Pats absorb alot more of the small square edged bumps and smooth out the ride but at the same time, they are most definitely going to give you more sidewall flex and roll in the corners. I suggest playing with the air pressure a bit and see if it will help the situation at all.

You went from a dual stage 2.5" MC coil to a 3 stage 3.5" RK coil. So, not only have you already raised your center of gravity up slightly with a larger (and softer) tire but you have now added an inch or more lift with the RK coils. The additional height alone will have some effect but so won't the design of the springs. The 2 stage MC coil acts like a single stage coil when driving around with the added benefit of a second stage that will extend to keep the spring seated when the suspension droops out. The RK coil is 3 stage. So it has a soft section of coil for when you are driving around, a stiff section of coil that comes into play when you compress the spring to help the suspension from bottoming and a 3rd stage of coil that is normally collapsed fully under the weight of the Jeep and only extends to keep the spring seated when the suspension is drooped out. This first/soft stage is probably allowing a little more floating that you have been accustomed too.

I'm going to mention here real quick... Did you, or have you, adjusted/replaced your sway bar links? If they are too short the sway bar doesn't have all its mechanical advantage it is supposed to have and therefore not the control over body sway/roll.

Shocks... I have found the Fox reservoirs to be a little soft. I have also driven some very stiff custom valved Fox shocks as well. Maybe it's worth having them re-valved to get a little more control over the suspension. For example I have RC coils, 38" C-rated Pats, and Antirock sway bars. My Jeep should be a mess! It's not... Why? Falcon 3.3 shocks. Even at the softer settings they are a fairly stiff shock. They work wonders at keeping my Jeep feeling almost sporty... Please don't think I mean like a Corvette.. I'm not crazy!

Then there are things like Caster? What is it at currently? You want 5.5 degrees or as close as you can get. If caster is too low it will get very darty/twitchy feeling. This can scare the crap out of you at highway speeds. It will feel like it would rather change lanes than go straight. White knuckle ride for sure!
With 3.5" of lift I am assuming you have a raised track bar mount? If not you will need to to get your roll center back. And if you did, did you flip the drag link as well? If not you will experience a ton of bump steer.

There are so many things that could be going on so take your time and eliminate what you can. There are a lot of similar builds on the roads that do drive perfectly fine so don't give up if your not satisfied. There are combinations of parts out there that will get you sorted out.


Fantastic feedback- thanks! Lots of leads there - Good thing I’ve got the winter to get it worked out.


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Discussion Starter · #15 ·
Lot's of sound insights on this thread. As @NC25T indicated, a raised JK on 37"s may not challenge a Corvette through the turns, but it should still be ok.

What tire pressure are you using? Which Nittos are you coming from (assuming Patagonia M/T)?

The step after that is to take a few hours and measure everything. String the car. check caster. Check all the fasteners on the suspension and steering. Check the wheel bearings. Make sure all the springs are fully seated. Most of this stuff has already been mentioned, but doing it all together often finds stuff missed earlier. The equivalent of a code review.

Did you measure the actual lift height front and rear, left and right, before and after? Is it really 1" or maybe more? Are those all JK springs or are they JKU springs by accident?


Yup I’ll start with PSI and then get to work on your list and the others provided here. Thanks all!


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If you flipped the steering, did you also raise the front trackbar?
As I read the thread, this was the question I was getting to the end to ask...

Also, it's mentioned above that a pro set it up, but did he put it on an alignment rack and verify the numbers? Need to see the alignment to confirm...
 

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Between the taller springs and bigger tires, you've raised the center of gravity. And...the short wheelbase 2-door certainly does its part in accentuating the instability. What you are feeling is physics doing its work (against you).

I actually went from a 3.5" lift to a 2.5" one to help keep my Jeep from feeling "tippy" on the street.
 

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I am going to side with Rich here. A lot is this is in the spring design, a little is in the height too.

If ya want RK 3.5" springs and 37's, it's probably gonna get a little spongy on the road around corners compared to what you are used to. 2 door SWB doesn't help. I remember each step up I made on each Jeep in the past once I got to this stage and I was like, "well I just made this thing a real PITA to drive on the street". Then I had up to go up another inch higher after that and another tire size because what the hell, it already sucked on the street, right? LOL. The spring rate is primarily done for the benefit of ride quality I think, but you have to drive it with the thought of not rolling it. Just takes a little getting used to. It doesn't sound like you missed anything as long as tire pressure is right.
 

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Lots of good input here.
I also would want to know what the actual caster number is. No disrespect to your professional guy, but numbers talk. There is a range that is considered "within spec", but sometimes within spec isn't good enough.
Also, the different tires may need different air pressures to feel right.
Finally, you may want to upgrade to a stiffer rear sway bar like the Helwig unit. If you have adjustable shocks, adjust them stiffer. If you don't have adjustable shocks either have what you have re-valved or try a different set of shocks (perhaps adjustable shocks).
But there is some truth to the point that if you keep raising the ride height and increasing the tire size it will not handle as well. The same quality suspension at a higher ride height won't handle as well.
 
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