TJ ride quality issue – spacers, mixed shocks, and minimum lift for 33s

[Efthimis Tj]

Read the responses. The ride quality is not effected by the springs or spacers, stop. Measure and replace all four shocks. A set of Rancho 5000 will suffice for quite some time but I believe they don’t last long enough with what I do to them. That said I do not have another shock recommendation.

I get your point, but obviously springs wouldn’t be changed at all if they played no role, everyone would throw a spacer in there.
I’m not arguing theory — I’m describing symptoms that strongly suggest the suspension is working outside of its usable travel. That’s why I asked if anyone here has experienced a similar spacer/shock length issue. If the case is that, I could remove the spacers and have a better ride till the new staff comes.
Thanks for your suggestion though, I will keep it in mind.

 

[jjvw]

I get your point, but obviously springs wouldn’t be changed at all if they played no role, everyone would throw a spacer in there.
I’m not arguing theory — I’m describing symptoms that strongly suggest the suspension is working outside of its usable travel. That’s why I asked if anyone here has experienced a similar spacer/shock length issue. If the case is that, I could remove the spacers and have a better ride till the new staff comes.
Thanks for your suggestion though, I will keep it in mind.

As already explained, spring spacers, when improperly sized and implemented, can absolutely disrupt the shock travel.

 

[GoldenGorilla]

My "money is not a limiting factor, but I want easy" recommendation is Rock Jock 2" springs. If that doesn't give you the ride height you want to clear your 33s, then get some 3/4" poly spacer/isolators. Once the springs are in, measure the length you need for the shock and order that length RS9000XL. If you end up between 2 sizes, for your intended purpose go with the shorter of the 2. That will give you some ability to set the ride in a way that is comfortable to YOU.

I run metric 285/75R16 33"s with Rancho's 2.5" spring and 3/4" energy suspension spring isolators in place of the factory rubber ones, not for leveling or added lift. I use the RS9000XL shock. The ride is good for a Jeep in my opinion and while it isn't going to be a killer rock crawler it can reliably do what I want it to do. I do struggle a bit with the RS9000XL setting in that I prefer the softer ride at setting 3, it can get kicked around a bit by high speed bumps like bridge seams or even the ridges between segments in a concrete highway and so I have settled on 4. I'd like dual speed compression control like I have on my MTB shocks, but I'm not sure Fox with DSC reservoirs are available or practical for a 2.5" lift TJ.

I don't know why this particular forum feels that spring rate doesn't matter when the entire motorsports world cares about it. It affects how much resistance the spring gives to bumps in the road as well as the ride height. For many the ride height is a primary consideration, but not for all. There is a balance between spring and shock resistance. A stiffer spring with a softer shock can feel similar to a softer spring with a stiffer shock on compression damping, but expect differences in rebound behavior between these two setups. If Rock Jock's published number of 70 lb/in is accurate and OME's 140 lb/in is accurate - that's a massive spring rate difference..

 

[jjvw]

...

I don't know why this particular forum feels that spring rate doesn't matter when the entire motorsports world cares about it. It affects how much resistance the spring gives to bumps in the road as well as the ride height. For many the ride height is a primary consideration, but not for all. There is a balance between spring and shock resistance. A stiffer spring with a softer shock can feel similar to a softer spring with a stiffer shock on compression damping, but expect differences in rebound behavior between these two setups. If Rock Jock's published number of 70 lb/in is accurate and OME's 140 lb/in is accurate - that's a massive spring rate difference..

RJ's 70lb/in is a combined rate vs OME's 140lb/in linear rate. These are two different calculations to describe two different types of coil springs.

The reason we argue and endlessly explain why spring rate is irrelevant is because when one designs a coil spring for a TJ that results in a typical ride height, this spring also must fit within the prarmaters of both needing to not go into coil bind before shock compression and also have a sufficient free length to not fall out at full shock extension. Within those parameters, there is only a narrow range of free lengths and spring rates that a spring can be made and result in the normal ride heights we are seeking. That range of spring rates is not wide enough to be perceivable in the ride quality.

 

[jjvw]

..., but I'm not sure Fox with DSC reservoirs are available or practical for a 2.5" lift TJ.

[...

Available yes. Practical, maybe not due to the compromises of a shorter shock.

DSCs will augment what is already there far beyond what a good tune will do with a remote reservoir shock.

A significant part of the goal behind the outboarding we do is to create suspension up travel in order to give the shock valving time and distance to do it's work. The typical 4" spring lift for 35s is what gets us 11" front, 12" rear shock travels divided 50/50 after an outboard. Less time and distance would require heavier damping. Lower ride heights will necessitate shorter shock travels which will provide less of a foundation for the DSCs to do their magic.

 

[Efthimis Tj]

My "money is not a limiting factor, but I want easy" recommendation is Rock Jock 2" springs. If that doesn't give you the ride height you want to clear your 33s, then get some 3/4" poly spacer/isolators. Once the springs are in, measure the length you need for the shock and order that length RS9000XL. If you end up between 2 sizes, for your intended purpose go with the shorter of the 2. That will give you some ability to set the ride in a way that is comfortable to YOU.

I run metric 285/75R16 33"s with Rancho's 2.5" spring and 3/4" energy suspension spring isolators in place of the factory rubber ones, not for leveling or added lift. I use the RS9000XL shock. The ride is good for a Jeep in my opinion and while it isn't going to be a killer rock crawler it can reliably do what I want it to do. I do struggle a bit with the RS9000XL setting in that I prefer the softer ride at setting 3, it can get kicked around a bit by high speed bumps like bridge seams or even the ridges between segments in a concrete highway and so I have settled on 4. I'd like dual speed compression control like I have on my MTB shocks, but I'm not sure Fox with DSC reservoirs are available or practical for a 2.5" lift TJ.

View attachment 664456

I don't know why this particular forum feels that spring rate doesn't matter when the entire motorsports world cares about it. It affects how much resistance the spring gives to bumps in the road as well as the ride height. For many the ride height is a primary consideration, but not for all. There is a balance between spring and shock resistance. A stiffer spring with a softer shock can feel similar to a softer spring with a stiffer shock on compression damping, but expect differences in rebound behavior between these two setups. If Rock Jock's published number of 70 lb/in is accurate and OME's 140 lb/in is accurate - that's a massive spring rate difference..

Thanks a lot for taking the time to write such a detailed response — I really appreciate it. We’re definitely on the same page. I also don’t quite understand why spring rate tends to get dismissed so easily. In various project cars I’ve worked on over the years (from drift-oriented builds to off-road setups), spring rate has always played a meaningful role in the overall balance together with damping. That said, your explanation about the TJ’s packaging constraints and how that naturally shifts the focus toward shock travel and valving makes total sense. Solid perspective, thank you.

PS nice ride by the way

 

[Efthimis Tj]

RJ's 70lb/in is a combined rate vs OME's 140lb/in linear rate. These are two different calculations to describe two different types of coil springs.

The reason we argue and endlessly explain why spring rate is irrelevant is because when one designs a coil spring for a TJ that results in a typical ride height, this spring also must fit within the prarmaters of both needing to not go into coil bind before shock compression and also have a sufficient free length to not fall out at full shock extension. Within those parameters, there is only a narrow range of free lengths and spring rates that a spring can be made and result in the normal ride heights we are seeking. That range of spring rates is not wide enough to be perceivable in the ride quality.

I understand the argument about the narrow practical window for spring rates on a TJ given coil bind and droop constraints, and I get why that leads many people to prioritize shocks. My intent wasn’t to argue theory, but to better understand where my current setup might be limiting usable travel and ride quality in practice. I appreciate the clarification.

 

[jjvw]

I understand the argument about the narrow practical window for spring rates on a TJ given coil bind and droop constraints, and I get why that leads many people to prioritize shocks. My intent wasn’t to argue theory, but to better understand where my current setup might be limiting usable travel and ride quality in practice. I appreciate the clarification.

Understanding the theory helps one understand the practical realities when working within constraints.

 

[GoldenGorilla]

RJ's 70lb/in is a combined rate vs OME's 140lb/in linear rate. These are two different calculations to describe two different types of coil springs.

If you have a divided dual spring with 2 140lb springs and you apply 70 lbs force to the system, each spring in the system will compress 1/2". Combined the total spring assembly will compress by 1". aka 70 lb/in. Mentally this is a bit weird as I think we're inclined to average them. They become dual rate by forcing one side to bind before the other. Without binding a side they follow this formula and act in net as a single rate spring;
CR = (TS*BS)/(TS+BS)

RockJock says this;

A key differentiator of RockJock spec. dual-rate springs is the positioning of the crossover point between the initial and secondary spring rates so that a portion of the softer initial rate is available and active at ride height before crossing over to the firmer secondary rate deeper into the travel.

I understand that in the Jeep market there are companies doing "dual rate" springs that are designed to sit with the top side in bind at ride height and function as a single rate spring with added free length (ie Metalcloak). Below applies to the RockJock true dual rate. In a one piece coil, you can't do 2 segments of 140 lb/in and get a 70lb combined rate.

One of the springs, typically Bottom Spring (BS) has to be greater than 140 in this formula to get a combined rate of 70.
CR = (TS*BS)/(TS+BS) or BS = (70*TS)/(TS-70)

Something like 131/150, 124/160 or 117/170. That first combined part of travel at 70lb/in is much softer than an OME spring. On a fixed shock that'll be a pretty big difference in feel versus the same shock paired with a 120lb/in or 140lb/in single rate spring. With single rate ranges between 120 and 160 many of these are double digit percent changes in spring rate and they should be noticable with the same shock same ride height. It's rare that people would do this in a jeep as it costs a bunch of money and takes time. The most common scenario where this has happened is someone doing OME standard and HD springs with OME shocks. And usually that was because they felt they needed the HD springs due to load and most that did it said - it rode different. And I suspect if I swaped to a Rock Jock 2" or 3" spring I would feel that I needed to turn up the compression setting on my RS9000XLs to maintain the same on road stability feel.

I have a background in racing mountain bikes (badly) going back to the 90s and am quite familiar with Fox DSC shocks and tuning them along with the added layer of rebound damping control on many forks. The cool thing on a mountain bike is that you can change a setting in a couple clicks, ride back up a section and get immediate tactile feedback to learn how low and high speed work together.

I also have a TPC Racing/DSS controller for the Bilstein Damptronic system on my other car, know how and what it does and how to tune it. Considering that tech existed in production at the end of the TJ era and that car is only 5 years newer than my TJ, it's pretty mind blowing what it does. It's available on modern offroaders today like the RAM TRX and certain Bronco models.

 

[jjvw]

If you have a divided dual spring with 2 140lb springs and you apply 70 lbs force to the system, each spring in the system will compress 1/2". Combined the total spring assembly will compress by 1". aka 70 lb/in. Mentally this is a bit weird as I think we're inclined to average them. They become dual rate by forcing one side to bind before the other. Without binding a side they follow this formula and act in net as a single rate spring;
CR = (TS*BS)/(TS+BS)

RockJock says this;



I understand that in the Jeep market there are companies doing "dual rate" springs that are designed to sit with the top side in bind at ride height and function as a single rate spring with added free length (ie Metalcloak). Below applies to the RockJock true dual rate. In a one piece coil, you can't do 2 segments of 140 lb/in and get a 70lb combined rate.

One of the springs, typically Bottom Spring (BS) has to be greater than 140 in this formula to get a combined rate of 70.
CR = (TS*BS)/(TS+BS) or BS = (70*TS)/(TS-70)

Something like 131/150, 124/160 or 117/170. That first combined part of travel at 70lb/in is much softer than an OME spring. On a fixed shock that'll be a pretty big difference in feel versus the same shock paired with a 120lb/in or 140lb/in single rate spring. With single rate ranges between 120 and 160 many of these are double digit percent changes in spring rate and they should be noticable with the same shock same ride height. It's rare that people would do this in a jeep as it costs a bunch of money and takes time. The most common scenario where this has happened is someone doing OME standard and HD springs with OME shocks. And usually that was because they felt they needed the HD springs due to load and most that did it said - it rode different. And I suspect if I swaped to a Rock Jock 2" or 3" spring I would feel that I needed to turn up the compression setting on my RS9000XLs to maintain the same on road stability feel.

I have a background in racing mountain bikes (badly) going back to the 90s and am quite familiar with Fox DSC shocks and tuning them along with the added layer of rebound damping control on many forks. The cool thing on a mountain bike is that you can change a setting in a couple clicks, ride back up a section and get immediate tactile feedback to learn how low and high speed work together.

I also have a TPC Racing/DSS controller for the Bilstein Damptronic system on my other car, know how and what it does and how to tune it. Considering that tech existed in production at the end of the TJ era and that car is only 5 years newer than my TJ, it's pretty mind blowing what it does. It's available on modern offroaders today like the RAM TRX and certain Bronco models.

I have a lot of experience in my early days of ownership messing around with multiple sets of OME coils and Currie stuff, including an early rare and unique set of 3" springs that may have not been a production set. Years ago ago for fun, when I changed from OME coils to Currie, I did the calculations using the published OME linear spring rates of the 2931 and 2949 coils I was using to estimate a corner sprung weights. Using those sprung weights, I then calculated my new Currie 4" coils as of they were a linear rate. I came up with 125lb/in front and 150lb/in rear.

Skipping over a lot of other testing and experiments, my big takeaway from running a lot of springs with a lot of different rates was that I looking extremely hard to find any difference in ride quality coming from the springs. Filling up the gas tank from empty is a bigger change than anything I thought was happening.

The moment I got a hold of a pair of used 12" Fox 2.0 RR with LSC adjustors with a very good tune to go into my first outboard project, I realized why effort to control ride quality through the springs was an absolute waste of time. The LSC adjusters did far more than anything I thought I knew before. Now with front shocks, 3-4 tunes later, and recently DSCs all around resulting in each iteration being a wildly dramatic improvement over the previous is why I adamately hold the position that in this application springs have no perceivable impact on ride quality. Nevermind that my tuner has never wanted to know my spring rates.

Anyone chasing ride quality must focus on shocks. This starts with sizing and setting them up properly to allow the valving to work. The build is centered around the shocks.

 

[Weasellee]

Anyone chasing ride quality must focus on shocks

I believe it to be that @jjvw is also speaking from experience. Do what you want but until the shocks are addressed the ride quality will not be effected much.

 

[jjvw]

I believe it to be that @jjvw is also speaking from experience. Do what you want but until the shocks are addressed the ride quality will not be effected much.

To be clear, I am not simply advocating for custom shock mounts and fancy shocks. Making sure the bolt on stuff works as well as it is able to is just as important.

 

[nondem]

Your descriprions of geometry in this particular application are irrelevant because no one is running a tall enough lift on a TJ that put the front leading short arms at steep enough of an angle to have any perceivable effect on the ride quality. This is why I have been requesting you to suggest an optimal length and angle for the arms to provide the optimal ride quality. You won't because you can't because you do not know where to go with your assertion.

I'm not sure what you mean. My assertion is factual and only goes as far as what I actually said. I stand by it. I'll give you the last word now because you obviously need it...

 

[jjvw]

I'm not sure what you mean. My assertion is factual and only goes as far as what I actually said. I stand by it. I'll give you the last word now because you obviously need it...

I will continue to offer you the last word on this. All you need to do is provide an optimal arm length and angle to improve the ride quality over a typical short arm build for 35s. Both front and rear arms.

This is your chance to shine!

 

[Weasellee]

To be clear, I am not simply advocating for custom shock mounts and fancy shocks. Making sure the bolt on stuff works as well as it is able to is just as important.

100%

 

[Superjay5]

To the OP, before you go pulling the coil spacers you need to cut the boots off the shocks and see how much shock shaft is exposed at ride height. If there is only an inch or 2 exposed, pulling the coil spacers will just make it worse, you would have zero uptravel.

That is really the first step in this process trying to improve your ride.