I have a questions about the Teraflex long arm kit. I would like to hear from Tera Flex along with others that have experience or opinions.

On the long arm kit, the upper arms are substantially shorter than the lower arms. Why is this? Was this based on limiting factors for locating the mounting points to the frame or for some other engineering reason?

It seems like at full droop the pinion would be point downward, potentially causing stress on the driveshaft and joints. Is this the case?

How does the longer arms effect the roll center and center of gravity? How about when climing or coming down steep inclines. It use to be that some long arm kits would allow the axle to drop too far, causing other problems, up to and icncluding rolling over. I have not heard this about the teraflex long arm.

Thank you for your input.

 

Control arms: Uppers are for setting pinion angle and the lowers are for lengthening the wheelbase, but if you change the length of the lowers with out touching the upper you also affect the pinion angle.

Driveshafts with long arms: It is advisable to upgrade driveshafts to a double cardan type to deal with the stress you mentioned during flex/droop.

Long arms and COG: Long arms help lower COG, but I fail to see how it would affect RC.

Hopefully a few other more knowledgable people here on the forum will chime in.

Hope this helps

 

Come on... there has to be more opinions out there.

 

Hi.

I'm not that familiar with the Terraflex LA kit but I fail to see how the arm themselves will alter the centre of gravity! Lifting the vehicle via taller/stiffer springs will raise the COG, as will taller tyres (tires). A body lift will too but to a lesser extent.

The roll centre will be affected primarily by the position of the panhard rod (track bar) and its axle/chassis bracketry. The standard adjustable track bars will have a small effect on the RC but used in conjunction with a lifted suspension kit will be at steeper angle than normal. Ideally the track bar should be flat with the vehicle at rest this will allow for minimal sideways movement as the suspension moves up and down through the arms travel arc.
Because you have a front and rear RC their relative height will also effect the vehicle. If the steering and suspension arms do not work in harmony then this can cause roll steer/bump steer/over steer/understeer etc.

The suspension and steering set up of any vehicle is very complex, way beyond my limited knowledge. On a jeep capable of driving at 100 mph closely followed by driving something off road as challenging as...(insert favourite trail) it taxes the design engineer severely.

It would be fairly straight forward to get a sheet of 8' x4' and mark out the pivot points, axle angles etc if you have the measurements, or find a member with the same set up and work it though some flexing terrain and carefully observe the pinion angles etc.

I found the local library invaluable when playing with suspension design with off road buggies years back.

Good luck,

Nick

 

I question the use of such unequal arm lengths by TF on there LA kit. Others have used longer upper arms relative to the length of the lower arms. I imagine it was done because it's easier and cheaper.

The longer arms will not affect the roll center. What affects the roll center is how the trackbar is handled. Lowering the trackbar mount at the frame side lowers the roll center - which is bad. Raising the trackbar mount at the axle end raises the roll center - which is good. TF lowers from the frame; this is a serious flaw in the TF LA kit and goes against all rational chassis engineering that I'm aware of. For me this alone eliminates TF from consideration. AT EJS nobody from TF could give me an answer as to why this was done.

To prevent unwanted, or excessive, body roll and unloading the inside tires you want the COG and the RC closer not further apart. The further above the RC the COG is the longer the "arm" of the higher COG acting on the RC and the more the vehicle rolls. The absolute best design available now for dealing with RC is the AEV Nth Degree lift. The handling is phenomenal; you should have been on the ride I went on! I don't own an AEV lift but if I were buying today I'd get their Premium lift and Currie or Clayton arms.

I hope the above made sense as it's kind of hard to explain with words and no diagrams.

BTW I talked to John Currie about long arms and he said that he didn't feel the JK needed them, but that since there seemed to be a demand for them, they may produce them sometime in the future.