this weekend we were testing the Truggy on the ramp for suspension bind, shock location etc etc, and noticed something odd.

when we were driving forward up the ramp, 100% of the flex came from the REAR axle. the front axle didnt flex at all.

when we BACKED up the ramp, 100% of the flex came from the FRONT axle.. the rear axle didnt flex at all.

on pauls TJ, when we ramp, both axles absorbe some amount of flex. however on the truggy, whichever axle was on the ramp stayed parallel to the hood of the truck, making the axle on the ground do all the work.

any idea why it would do this? we have a 3 link suspension both front and rear, and each axle articulates very well, however on our first try we were unable to get them to work together, sharing the overall flex.

why clue how to make the axles cooperate better so they share the work? this is the first time ive run across this...

http://chrispy.rockcrawler.com/pics/paul2/Jul14_30.JPG in the above picture, the front axle has not moved at all, and the rear axle is almost totally articulated.

and below the front is fully stuffed and articulated, and the rear is again, perfectly parallel to the frame.
http://chrispy.rockcrawler.com/pics/paul2/Jul14_23.JPG

when the TJ below ramps, both axles seem to share the work...
http://chrispy.rockcrawler.com/pics/paul2/Jul14_31.JPG

Swaybars. No, not the big thick suckers jeeps come with stock, but nice soft, adjustable models similar to the AntiRock from Currie. (for TJ's) You could modify an AntiRock, or put together what you need from www.stockcarproducts.com.

Originally posted by ChrisPy
this weekend we were testing the Truggy on the ramp for suspension bind, shock location etc etc, and noticed something odd.

when we were driving forward up the ramp, 100% of the flex came from the REAR axle. the front axle didnt flex at all.

when we BACKED up the ramp, 100% of the flex came from the FRONT axle.. the rear axle didnt flex at all.

on pauls TJ, when we ramp, both axles absorbe some amount of flex. however on the truggy, whichever axle was on the ramp stayed parallel to the hood of the truck, making the axle on the ground do all the work.

any idea why it would do this? we have a 3 link suspension both front and rear, and each axle articulates very well, however on our first try we were unable to get them to work together, sharing the overall flex.

why clue how to make the axles cooperate better so they share the work? this is the first time ive run across this...

http://chrispy.rockcrawler.com/pics/paul2/Jul14_30.JPG in the above picture, the front axle has not moved at all, and the rear axle is almost totally articulated.

and below the front is fully stuffed and articulated, and the rear is again, perfectly parallel to the frame.
http://chrispy.rockcrawler.com/pics/paul2/Jul14_23.JPG

when the TJ below ramps, both axles seem to share the work...
http://chrispy.rockcrawler.com/pics/paul2/Jul14_31.JPG spring rate must be to stiff ,but screw the ramp take it riding then see how you like it i bet it will be ok.:smokin:

That is an interesting observation. Mine does the same thing but I never really thought about it until now. I think it might have something to do with center of gravity. The truggy has a higher center of gravity than the Jeep. When you climb the ramp, more weight is transfered (shifted) the the opposite corner of the tire climbing the ramp.

i thought about that, but i run a leaf sprung, sprung over, big ass scrambler, with similar wheelbase and lift height to the truggy, and both axles articulate on the ramp. i dont know precisely what spring rate im running on either vehicle tho..

anyone know the exact spring rate of stock front springs off an XJ?

so perhaps softer springs all the way around?

Softer spring rates will help (XJ stock fronts are 155-165 #/in).

The light unsprung weight amplifies the perception that it's not working, while the trail performance may be way better than you expect for the ramp result. Get it on the trail before you get too excited and make changes.

The real problem (if it is a problem to you) is the high roll center with the lift height and linkages. The high ramped end of the vehicle places the roll center of the linkage near the CG of the (raised) vehicle, with no working leverage through the suspension. The low end of the vehicle has the (now raised) CG a little more elevated above the roll center, increasing the CG to roll axis (roll center) leverage on the lower end axle & suspension.

Compare the angle (in relation to the horizion) of the Truggy and TJ control arms in your ramp pictures, to make an educated guess of the roll center difference (front vs rear, with either end on the ramp). Flat (or inverted) arms determine a level (or lower) roll center with more leverage for the CG to work the suspension. Look at the high and low end arm positions, compared to each ends ability for the system to articulate. You may well confuse a few suspension "experts" (funny how photos can illustrate concepts when words cannot).

Lowering the elevation of one plane of the linkage frame mounts (upper or lower link pins), or raising the axle end mounts, will lower the roll center of that system, providing more leverage for the system to articulate. The drawbacks are possible lower ground clearance, and a possible need for higher or progressive spring rates (and the potential for more problems if you do not think it through: more squat under power, poor IC length from the axle CL, etc.).

Leaf sprung suspensions typically articulate well because the roll center (and axis) is somewhere between the axle centerline and leaf end height, much lower than the frame (the mounts for the linkages and the instant center of a steeply angled linkage system).

Again, wheel it before making a decision to change, it may surprise you.

Happy Trails!

The way your rig drives up forwards looks fairly good to me. Getting that much articulation overall is a lot. And whats happening is the body it leaning over to the right and gravity makes you get less flex on the front and more on the rear cause you are getting some body roll to the right. Whats does it look like when you drive it up too less heights?? If you watch carefully you should be able to see how both ends work at the start then as you drive up further how gravity leans the body to the right.

When you back up it does look fairly bad. It also looks like its only driving up about half as far. Most of the weight is on the front axle and the rear has done nothing and all the flex is from the front. At this ramp height I dont think gravity or body lean is doing it what I think is that the rear is too stiff for the front (or the front too stiff for the rear).

So IMO the reason it does what it does driving up forwadrs is that you are ramping so far that gravity is leaning the body to the right and making it square up on the front axle (this always happens) I think at lower ramp heights you will get a better idea of how the suspension works together.

The reason it does what it does driving up backwards is that the front springs are too soft in comparison to the rear.

I think that you also got a lot of front weight compared to the rear which makes it hard to get the suspension to behave it self at tall ramping heights. Use the ramp to check binding etc of the suspension. The ramp is good for this cause it will always max out the suspension of the axle on the ground. If you want to use the ramp to get an idea of how balanced the suspension is dont do it at your maximum ramping height cause it wont mean much. I think you are better of using a height where the wheel is about 3-4 feet off the ground and then you can check your balance there.

I still think you need stiffer front springs.

:beer:

Sam

Im no expert, and may just be talkin out my ass, but seems to me a low roll center would cause this. IMO, its getting the same effect as excessive body roll on a side hill, CG is shifting over to the tire on the opposite side of the ramp, same axle...but WTF do I know?

Thanks Alot guys. thats the info i was looking for.. and YES, were gonna Rock this thing before cutting it up.

strange: your suspision is ours also. the rear springs on that are front xj springs. why? well we had em in the basement. new springs are in teh works.. but we wanted to get it on the trail first before guessing at springrates and such