4-Link - Mitigating Steep Roll Axis

Nay · Apr 22, 2004

I've done all the reading on all the theads about this topic. I know more than I ever thought I would about AS, IC, CG, and WTF. What I haven't seen is a solution, besides the buggy route, to deal with steep roll axis.

Kaz is telling me that rear coilovers might be the solution. I get the rest of it, and I like the overall advantages, but flopping it on it's side because of roll axis issues is a deal breaker, and I don't understand technically how coilover performance differs from spring/shock performance. For those who have done the 4-link with standard "under the frame" mounts for both uppers and lowers, what was your solution (if you have found one?). And can someone post a "coilovers for dummies" explanation?

Thanks,
Nay

JnJ · Apr 22, 2004

Here ya go!

Beezil · Apr 22, 2004

Nay said:
but flopping it on it's side because of roll axis issues is a deal breaker
Nay

if flopping your jeep on its side is something you aren't ready for, then you probably don't need to worry about the whole 4-link/coil-over thing......

a nice, flat quality leaf spring pack in the rear is still extremely effective. The best performance i got out of any xj that I was afraid to roll was when it was equipped with spacer-boosted 4.5" re coils and a 10-leaf national spring pack and a 2" tapered block and mj shackles.

theres no reason to strap on a 4-link and coilovers on a family touring jeep

BrettM · Apr 22, 2004

coilovers do not change suspension geometry, though with proper tuning, they may be able to mask some of the quirks

ashmanjeepxj · Apr 22, 2004

mad maXJ said:
coilovers do not change suspension geometry, though with proper tuning, they may be able to mask some of the quirks

Reguarless of geometry, roll axis, IC.....WTF..

On a flat leaf spring, like my whole RIG... the leaf springs resist up travel, but they also resist down travel.. I like that posative resistance on down travel, it puts more force on the other tire while one is hanging in the air....Less flex but who cares. I dont like leafs cause they have bad axle control that leads to bad traction...This points to a 4 link with coilovers as a spring option...

normal coil springs on a 4link, if retained at the top and bottom will do the same thing as my leafs. They will like a slinky resist down travel, but the 4 link will provide better axle control. I think even a bad designed 4 link within reason will have better traction then leafs...

Coil overs act different then a normal coil fixed at each end...
Example: If you put your High jack on your rear bumper with coil overs, your axle will drop till the shocks bottom out.

With leafs or a retained coil setup it will drop but not completely, your shocks could allow another few in of down travel if forced when articulated.

It would take a center limiting strap to limit axle drop, and a sway bar to have the same responce with Coilovers.
Coilovers can be better becuase they are adjustable, Dual rate coils you can swap out different rate coils, you can adjust how much uptravel for each rate, you can easily adjust ride height, you can adjust your center limiting strap, and you can try different positions on a swaybar....

Nay · Apr 22, 2004

ashmanjeepxj said:
I dont like leafs cause they have bad axle control that leads to bad traction...This points to a 4 link with coilovers as a spring option...

normal coil springs on a 4link, if retained at the top and bottom will do the same thing as my leafs. They will like a slinky resist down travel, but the 4 link will provide better axle control. I think even a bad designed 4 link within reason will have better traction then leafs...

How well do coils "resist down travel"? Does stretching coils decrease lifespan? I'd think this would also help excessive side lean.

Thanks for the input.

Nay

BrettM · Apr 22, 2004

ashmanjeepxj said:
Reguarless of geometry, roll axis, IC.....WTF..

On a flat leaf spring, like my whole RIG... the leaf springs resist up travel, but they also resist down travel.. I like that posative resistance on down travel, it puts more force on the other tire while one is hanging in the air....Less flex but who cares. I dont like leafs cause they have bad axle control that leads to bad traction...This points to a 4 link with coilovers as a spring option...

normal coil springs on a 4link, if retained at the top and bottom will do the same thing as my leafs. They will like a slinky resist down travel, but the 4 link will provide better axle control. I think even a bad designed 4 link within reason will have better traction then leafs...

Coil overs act different then a normal coil fixed at each end...
Example: If you put your High jack on your rear bumper with coil overs, your axle will drop till the shocks bottom out.

With leafs or a retained coil setup it will drop but not completely, your shocks could allow another few in of down travel if forced when articulated.

It would take a center limiting strap to limit axle drop, and a sway bar to have the same responce with Coilovers.
Coilovers can be better becuase they are adjustable, Dual rate coils you can swap out different rate coils, you can adjust how much uptravel for each rate, you can easily adjust ride height, you can adjust your center limiting strap, and you can try different positions on a swaybar....

regular coils will only resist droop after they have reached their unloaded height, which is only at the extremes of flex, up until that point they are pushing down on the axle.

same with leaf-springs, they only limit down-travel after they have reached their unloaded height.

if you got the money for coilovers, you got a couple extra dollars for limiting straps.

Kaczman · Apr 23, 2004

mad maXJ said:
regular coils will only resist droop after they have reached their unloaded height, which is only at the extremes of flex, up until that point they are pushing down on the axle.

same with leaf-springs, they only limit down-travel after they have reached their unloaded height.

if you got the money for coilovers, you got a couple extra dollars for limiting straps.

If you use shorter, stiffer coils, the resistance will come into play much sooner than you think. The compressed/uncompressed lengths of stock XJ coils my rear 4 link is less than 3" of difference. I have ~10" of drop with some degree of coil resistance.

Yes, I do have too much down travel, and I will also be switching to stiffer coils. But with some minor tuning, I believe I can get the right spring rate. Stretching the coils from being captured will eventually decrease the spring life span, but used XJ lift springs are a dime a dozen.

-Jon

Beezil · Apr 23, 2004

nay.

just roll and get it over with.

I swear you will feel MUCH better.

KY Chris · Apr 23, 2004

Beezil said:
nay.

just roll and get it over with.

I swear you will feel MUCH better.

Rod Stewart voice on: "The first cut is the deepest..."

Nay · Apr 23, 2004

Beezil said:
nay.

just roll and get it over with.

I swear you will feel MUCH better.

Rolling isn't the end of the world...I'm putting in a cage on Monday. I have a pimpin' minivan now - the Jeep can be "dedicated" now.

What I'm after is something of a family buggy. Meaning: the wife and kids can all ride, strapped into their five point harnesses, for trails that are worth taking the kids along, like Moab. This means no ridiculous body roll on off camber ledge roads scaring the pants off of everybody.

It also means being able to play on the more serious stuff, and to do the occasional "family stays home" trail. An optimized leaf setup "might" be better for this goal (flat leaf/block/traction bar)...but that's why I'm asking.

It sounds like stiff rear coils with limiting straps at the point the coils unload would provide a sweet front to rear balance without too much flop tendency. Limiting straps are cheap. I'm after 10-11" of front to rear balanced shock travel...and have maybe half that in the rear suspension right now and all of it up front. The question is simply how to achieve the rear suspension goals without inducing ugly side effects.

Nay

Beezil · Apr 23, 2004

no one has gotten on my ass for saying this yet, but here goes:

anyone can make a double triangulated suspension system fit on the back of an xj easily.......

but if you want one that actually prioritizes geometry over "making it fit" with nice, horizontal angles and attention to roll axis, you are gonna hafta cut through the floor and send your top links to some point inside the cabin and constructing link tunnels and such. Probably not something you'd be interested in with backseat passengers.....I see avoiding this as a compromise, which begs the question, why bother messing with the rear at all? flat leaf springs work very well.

Nay · Apr 23, 2004

Beezil said:
no one has gotten on my ass for saying this yet, but here goes:

anyone can make a double triangulated suspension system fit on the back of an xj easily.......

but if you want one that actually prioritizes geometry over "making it fit" with nice, horizontal angles and attention to roll axis, you are gonna hafta cut through the floor and send your top links to some point inside the cabin and constructing link tunnels and such. Probably not something you'd be interested in with backseat passengers.....I see avoiding this as a compromise, which begs the question, why bother messing with the rear at all? flat leaf springs work very well.

That's why I was asking...can you accomplish the goals without the cabin intrusion scenario (no need to trade one compromise for another IMO)? Appears the answer is "no", so I'll probably focus on a "flat pack" setup at some point.

Thanks for the input.

Nay

Kaczman · Apr 24, 2004

Nay said:
That's why I was asking...can you accomplish the goals without the cabin intrusion scenario (no need to trade one compromise for another IMO)? Appears the answer is "no", so I'll probably focus on a "flat pack" setup at some point.

Thanks for the input.

Nay

You "could" get a flatter roll axis, but your roll center and link mounts would be very low. Roll axis is only one concept to be concerned about. Without cutting, there is always a compromise.... Pick your poison.

I do think you may be able to have a bit less intrusion into the cabin than Beezil did (when the body was still attached). But once again, if you need to cut anyway, why compromise.

-Jon

Kaczman · Apr 25, 2004

OK.... More link nerd talk.

I lowered the Beep from ~8.5" lift to ~6.5" and recalculated the rear link numbers. It looks promising. The roll axis dropped from 9.16 degrees to 5.5 and the antisquat is now at 110%. I also cut down my old Tomken 5.5" front springs for new stiffer rears.

In the initial test drive through the neighborhood, the springs rates felt more balanced, and highspeed turns no longer wanted to jack the driver's front tire. Body roll is now significantly less.

I initially thought I couldn't clear 38's with less than 8" of lift, but with the current body trimming, I will have no trouble at 6.5". Hopefully I'll be able to hit the trails tomorrow and do more testing and tuning, but I hope to be on the right path.

-Jon

vintagespeed · Apr 25, 2004

Beezil said:
anyone can make a double triangulated suspension system fit on the back of an xj easily.......you are gonna hafta cut through the floor and send your top links to some point inside the cabin and constructing link tunnels and such.....

Ok, so here's the question. Why did you have to cut through the floor to get the proper angle? Why couldn't you have just raised or lowered the axle ends? It would do the same thing for "angle".

Beezil · Apr 25, 2004

I did.

my lowers are 1.5" above the TOP of the axle tube......my uppers are 7.5" above that.

Kaczman · Apr 26, 2004

Did you want the links high strictly for clearance or to get the roll center higher? And, is your roll axis flat?

-Jon

4-Link - Mitigating Steep Roll Axis

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