A TieRod Theory

I have been thinking about Project X and the bending of two idler arms in TN. After looking closely at the tie rods and the angles achieved from the lift, I have come to a conclusion.

It would appear to me that the primary cause of tie rod and IA bending is not so much the rims and tire size, but primarily the angle of the tie rods to the IA. In the sharp angle they are now, when I jump up on a rock, it sends a jar through the steering system that is transferred to the tie rod. Normally, this would be exhibited in a side to side movement that would apply pressure to the strongest side of the IA and tie rod if the tie rod angle is straight across. In my lifted Project X, the angle of the tie rod alters the angle of force to the IA. This is putting upward pressure on the IA and since at the moment it is the weakest link, the IA bends since it wasn't designed to protect against upward pressure. This problem is compounded by the increased tire size as well as the altered weight center of the tire/wheel combination.

The following drawing illustrates my theory:

http://www.warmongr.com/photos/tierod.gif

As you can see, in theory decreasing the angle of the tie rods will alter the pressure point on the tie rods and IA from up and down to side to side. Since I am running 16" wheels with a slightly reduced backspacing, I have the ability to space my tie rods upward to reduce the angle and relieve the pressure. It is a project I am now working on. But I am wondering what others think of the soundness of this theory.

Here's my reply from XOC, since it's not in a "parts" forum...

Yeah, this is what we've been talking about all along. It's also the reason the idler arm pivot joint wears out so quickly. The pitman arm joint is a ball joint, and doesn't suffer as much.

In actuality, 'when you jump up on a rock' (WTF ???) the force starts at the knuckle, then travels through the tie-rod, pushing the center relay rod upward (while trying to rotate it, remember, the pitman side is a ball joint), pulling the idler and pitman with it.

Spacing the tie-rods upward by simply moving the outside link will cause excessive bumpsteer, since the angle will no longer be in phase with the travel of the lower control arm.

The only way to stop this problem is to not lift the truck, replace the steering system, or not 'jump up on rocks'.

I never really understood bumpsteer, so I did some searching and found this explanation that I thought was very good and decided to share it.

Richard


A very quick, grossly oversimplified word on bumpsteer, and why you don't want it. Bumpsteer is cause by the control arm and the tie rod following differing arcs as the suspension goes through its travel. In the case of the stock Mustang setup, you can see that the tie rod lies at more of an angle to the ground than the control arm.

Imagine the control arm moving up in response to a bump. The arm moves through its arc, and the tie rod moves through its slightly more advanced arc. But the angular difference between the two causes the tie rod end to actually cause the wheel to toe in as the suspension goes through bump, and toe out as it goes through droop, which changes the steering angle of the wheel and makes the car respond exactly as if the steering wheel had been turned by a minute amount.

If the suspension movement is caused by body roll, as in high speed cornering, the inside wheel will actually change towards toe-out, and the inside wheel goes into toe-in. If it's caused by dive, as in hard braking, both wheels go towards toe in. This causes your steering inputs to be modulated by bumps, and leads to a certain degree of nervousness on the part of the steering. In any case, it is entirely undesirable, since as a driver you really want the car to react the same way to steering inputs regardless of suspension position.

My neighbor & I were brainstorming & came up with this idea:
Make sort of a "drop" tie rod assembly.
Poor man's version: take the inner & outer tie rod ends & weld a block of steel on top of the outer tie rod & on bottom of inner tie rod.
Next, tap these chunks of steel to fit the stock tie rod adjuster or even a larger diameter tie rod adjuster if you so desire (larger diameter tie rod adjuster would require larger "blocks" of steel to be welded on).
The end product would look sort of like this:

http://files.automotiveforums.com/uploads/857979TieRodImage.jpg

It seems that this would solve a bit of the problem assuming the following suppositions:
--the tie rod ends are kept fairly flat relative to the ground so the joint at the center link is not at a harsh angle so no torquing of the center link (strong momenets will be on the welds holding the block to the tie rod ends),
-and-
--the angle of the *imaginary* straight line between the inner & outer tie rod pivot points is the same as that of the lower control arm, therefore no bump steer.
The total offset should equal the amount of lift of the front end & this can be split between the inner & outer ends (i.e. 1" offset per end for a 2" lift)
This seems to me like a cheap & effective method but I wanted to get everyone's opinion...
--jim.

Originally posted by xterrabull
--the angle of the *imaginary* straight line between the inner & outer tie rod pivot points is the same as that of the lower control arm, therefore no bump steer.

Due to that exact reason, it would not help the problem.

You are still sending the same force from the outer pivot point to the inner pivot point in your diagram. No matter how it gets there, it will cause the same amount of stress on the center relay rod.

I will add one other problem to what Ian has said. If you look closely at the relay rod where it and the tie rods meet, you will see there is not enough room to do what you propose. I have been reviewing the problem with a friend who does fabricating for a living and the prognosis is not good. Short of doing a Chevy style lift, this is going to be an on-going issue with the X/Frontier. I am working to move the bending from the idler arm to the tie rods. The tie rods are far easier to replace on the trail and can easily be pre-measured for sides and slapped in with no alignment worries. The less time I spend repairing @#$% that breaks, the more time I spend on the trail.

damn...can't have one w/out the other, huh? :mad:
As for clearance from frame of inner tie rod welded on steel block, the block could be made quite short so long as there's no problem with the tie rod adjuster poking out the other end (i.e. there'd be a tapped thru-hole in the block)...still don't know if this would help enough, though.
Anyways, the point is quite moot....

So, perhaps the CHEAPEST solution is to customize the idler arm/center link interface incorporating wearable & replaceable parts (bearings, bushings).
I just don't want to spend $850 on the heim setup bandied about on the XOC "Hardcore 4WD" thread -- it seems to me that the problem doesn't warrant THAT much of an overhaul....
I dunno...I guess just wait & see what the handful of relevant companies makes available....

Originally posted by xterrabull
I just don't want to spend $850 on the heim setup bandied about on the XOC "Hardcore 4WD" thread -- it seems to me that the problem doesn't warrant THAT much of an overhaul....


You wont have to, that $850-900 price tag is inflated to say the least. There are only $300 worth of parts in that setup, and I don't see $600 worth of labor. The initial R&D is expensive, but that shouldn't punish the consumer.

SLR has a couple solutions coming, and so does CALMINI.