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Unread 01-21-2014, 02:10 PM   #1
pierps
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Body Roll & Nose-diving: is it my shocks or springs?

Hi all,

Before I get into background/my question:

Yes, my sway bars are connected (stock sway bars, jks quicker discos up front).

I'm trying to work out a plan to address what I consider to be excessive body roll and nose diving under braking. My jeep is pretty wobbly around corners and the nose dives excessively (IMO) under braking. It doesn't bounce after going over bumps and the shocks don't appear to be leaking.

Rig's relevant specs:

1998 TJ Sport
Rancho 2.5" short arm lift with RS5000 shocks (installed in like 1999!; I have no idea what the spring rates are)
ARB front bumper with winch
1.25" body lift
33x10.50's on 15x8 rims with 4.5" backspace

Here's a pic just because (it just underwent a significant refurb- my parents gifted this jeep to me after leaving it sitting for a few years with a water leak in the cabin- yuck).



I have two points of reference:
1. A friend back in high school (wow that was a long time ago now!) drove a '97 sport with an OME lift on it. It rode really nicely- basically exactly what I'm looking for. It was firm and felt stable around corners and under hard braking.

2. I currently also drive a '76 FJ40 (gasp- it's not a jeep!). 3" lift, leaf-sprung, 35's. The thing is super top heavy and way taller than my jeep. Despite its other handling challenges, even the FJ40 feels more stable going around corners than my jeep does.

I've read tons of threads about the role of shocks and springs. Most say that shocks have a bigger impact on handling than springs. The jeep has ridden very softly from the day they installed the lift in '99, so I suspect it's just by design.

Is my body roll and nose-diving a function of my shocks, springs, or both? If I only need shocks, I'd like to just buy shocks and not go through the hassle of redoing the lift. If I need springs and shocks, I'd rather buy the OME kit as a package deal since it's cheaper than buying things piecemeal.

What say you?

Thanks!

Peter

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Unread 01-21-2014, 02:14 PM   #2
pierps
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PS- I know the jeep looks really raked in the picture- this is because it's parked on a hill, and I hadn't installed the hard top or doors yet. With everything on, it sits pretty level (with a slight factory-like rake).
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Unread 01-21-2014, 02:39 PM   #3
hustler905
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Springs won't make it roll, shocks will.
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Unread 01-21-2014, 03:37 PM   #4
pierps
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Thanks!

Just so I understand: All else equal, if I take two perfectly identical TJ's, install soft springs on one and stiff springs on the other (using the same shocks on both identical jeeps), you're saying they will both have the same amount of body roll and nose-diving?

I'm trying to wrap my head around that because it's counter-intuitive to me. It seems to me that the softer springs would result in more body roll for the same reason that pushing down on the jeep would cause more compression on the softer springs.

Thanks

Peter
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Unread 01-21-2014, 03:38 PM   #5
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Quote:
Originally Posted by hustler905 View Post
Springs won't make it roll, shocks will.
I agree. Worn shocks or to light of a shock will allow it to roll and dive.
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Unread 01-21-2014, 03:44 PM   #6
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Quote:
Originally Posted by pierps View Post
Thanks!

Just so I understand: All else equal, if I take two perfectly identical TJ's, install soft springs on one and stiff springs on the other (using the same shocks on both identical jeeps), you're saying they will both have the same amount of body roll and nose-diving?

I'm trying to wrap my head around that because it's counter-intuitive to me.

Thanks

Peter
The difference between "soft" springs and "heavy" springs is the ability to support more weight without sagging, when you hit a bump or your brakes, you are loading up the springs so much that it's way beyond the difference of being able to carry 500lbs or 1000lbs, you're putting thousands of pounds of force onto the springs at a rather fast rate, which is where the shocks come into play. Lot's of force applied at a fast pace equals a shock to the system... shock absorbers, hence the name, take that fast moving large force, and convert it into heat, and dissolve that into the fluid inside the shocks... I'm being pretty basic and simple, but the shock has a lot more to do with swaying and diving than the springs do.
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Unread 01-21-2014, 03:48 PM   #7
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It's a system made up of many variables! Be suspicious of the the single point solutions.
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Unread 01-21-2014, 03:56 PM   #8
pierps
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Quote:
Originally Posted by Necromancer_tat View Post
The difference between "soft" springs and "heavy" springs is the ability to support more weight without sagging, when you hit a bump or your brakes, you are loading up the springs so much that it's way beyond the difference of being able to carry 500lbs or 1000lbs, you're putting thousands of pounds of force onto the springs at a rather fast rate, which is where the shocks come into play. Lot's of force applied at a fast pace equals a shock to the system... shock absorbers, hence the name, take that fast moving large force, and convert it into heat, and dissolve that into the fluid inside the shocks... I'm being pretty basic and simple, but the shock has a lot more to do with swaying and diving than the springs do.
Ah. That makes a lot of sense- very clear explanation. Thanks!


Quote:
Originally Posted by ftgiles View Post
It's a system made up of many variables! Be suspicious of the the single point solutions.
Yeah, I figured as much. In this case, I'm leaning toward getting RS9000xl's since it allows me to dial in the stiffness of the shocks to taste. If I decide I want those shocks no matter what, then the cost savings of buying the full OME kit becomes a non-issue.

If I'm still unhappy with the body roll/etc after the new shocks, then I can go ahead with the OME heavy duty springs.

I think that's what I'll do.

Now I need to figure out why my steering feels so soft (too easy to turn the wheel). I want to feel more of the road. I'm thinking I need to adjust caster and get a stiffer steering stabilizer.

I guess the pattern is that I like more response and connection to the pavement. Probably the result of driving german cars for so long!

anyway, back on topic. Thanks guys- I'm going to order some RS9000XL's and go from there.
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Unread 01-21-2014, 04:04 PM   #9
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I'd suggest that while range of spring rate gets talked about a lot here that realistically the options available for TJs are not that great and don't vary enough to make a big difference, thus the focus on shocks. Contrast this to say racing coilover setups where a lot more length and spring rate options for both the upper and lower spring.

As to the Ranchos, while I was happy with them when I ran them I honestly think the range of adjustability gets a little exaggerated. Look through the threads discussing and I think you'll find most people set them once in the 2-4 range and don't touch them after that. Oh, and be careful what length Rancho's you order. I think if you go by their recommendation you end up with long shocks and limited up travel.
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Unread 01-21-2014, 04:08 PM   #10
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Remember shocks only resist changes in momentum. They can't magically prevent diving, but stiffer shocks will change the speed at which it occurs.

At the heart of it, diving is a factor of suspension geometry just like squat and anti-squat while body roll is a factor of sway bars AND suspension geometry.
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Unread 01-21-2014, 04:15 PM   #11
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Quote:
Originally Posted by biffgnar View Post
As to the Ranchos, while I was happy with them when I ran them I honestly think the range of adjustability gets a little exaggerated. Look through the threads discussing and I think you'll find most people set them once in the 2-4 range and don't touch them after that.
Thanks for the response.

Do you mean that the difference between the softest setting and the stiffest setting is negligible? Or are you just saying that most people "set it and forget it"?

I fully plan to "set it and forget it" after some initial test-driving. I just want to be able to set the stiffness to my liking. Otherwise, I have to rely on the opinions of those on the boards, which seem to vary wildly from "your rig will handle like a porsche if you remove your sway bar" to "even the softest shocks on the market are too stiff." In other words, it's really subjective.

If you're saying that the range of adjustibility is insignificant, then yeah- why pay the premium?
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Unread 01-21-2014, 04:20 PM   #12
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I wouldn't recommend the Rancho 9000xls for controlling dive or sway. I have them now and if I set them firm enough to prevent dive and sway they are pretty harsh riding. If I set them to be soft riding, I experience lots of dive and sway. I ran the Fox racing shocks on one of my previous builds, and they were only slightly more expensive, but they controlled dive and sway much better without riding to harsh. I hear that the Fox resivour shocks are even better, plus they can be custom tuned as well. I'm planning on upgrading to those after I get the rest of my rig completed so I know what the weight will be at each corner so the shocks can be tuned accordingly.
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Unread 01-21-2014, 04:22 PM   #13
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Quote:
Originally Posted by pierps View Post
Thanks for the response.

Do you mean that the difference between the softest setting and the stiffest setting is negligible? Or are you just saying that most people "set it and forget it"?

I fully plan to "set it and forget it" after some initial test-driving. I just want to be able to set the stiffness to my liking. Otherwise, I have to rely on the opinions of those on the boards, which seem to vary wildly from "your rig will handle like a porsche if you remove your sway bar" to "even the softest shocks on the market are too stiff." In other words, it's really subjective.

If you're saying that the range of adjustibility is insignificant, then yeah- why pay the premium?
The difference between the softest setting and the hardest setting is very noticeable. The softest setting feels like you don't have any shocks at all, and the hardest setting feels like you don't have any springs at all. Unfortunately it's kinda hard to find a nice inbetween setting. I'm still experimenting with mine.
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Unread 01-21-2014, 04:29 PM   #14
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Quote:
Originally Posted by pierps View Post
Thanks for the response.

Do you mean that the difference between the softest setting and the stiffest setting is negligible? Or are you just saying that most people "set it and forget it"?

I fully plan to "set it and forget it" after some initial test-driving. I just want to be able to set the stiffness to my liking. Otherwise, I have to rely on the opinions of those on the boards, which seem to vary wildly from "your rig will handle like a porsche if you remove your sway bar" to "even the softest shocks on the market are too stiff." In other words, it's really subjective.

If you're saying that the range of adjustibility is insignificant, then yeah- why pay the premium?
The difference is noticeable. I just don't recall seeing anybody find 1,2 or 5+ acceptable. So is adjustability that nobody uses still a cool option? Your call.
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Unread 01-21-2014, 04:30 PM   #15
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Right now I only have the rear RS9000s but the difference from 1 to 9 is definitely noticeable. For me personally I went with them because I wanted a quality shock with options. I'm not at the point in my build where I want to outboard. If I was no doubt I would be going with custom tuned Fox shocks.
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