Tension Rods - T3 vs FutoFab - Real world use thoughts

[5NDIME]

I am at the point where I'm about to order a set of tension rods. I have seen the previous discussion of these from a couple years ago, but am wondering what people think having used these the past couple years. I have T3 camber plates and 280ZX coilovers, but I will say Dave's stuff all looks solid too. Anyone have some good input after using either of these tension rods over the past couple years? Anyone really having bumpsteer issues with the T3 due to the shorter length of the rod from pivot point to the LCA? I'm going to be using them on a street car with light track use now, but would like to use them when I do get to the point of stripping the car down to track it.

[Dime Dave]

Let me comment on why a clevis and mounting bracket is used on FutoFab’s Adjustable TC Rods, plus some recent improvements we’ve made.

 

We use a clevis to create a pivot point between the TC Rod and LCA. This allows the angle between two parts to change as the caster is adjusted. If the TC Rod to LCA connection were rigid, it will create a bending strain in the TC rod when any adjustment is made after installation. By having a pivot action at the clevis, no bending stress is placed on the TC Rod regardless of the final caster setting.

 

We have changed the clevis to a 5/8-18 LH thread for ease of adjustment. Our earlier design required a multi-step process if adjustments were significant. Now adjustments over the full range are done in one step. You unlock the jam nuts, rotate the link to adjust length and relock the jamb nuts.

[thisismatt]

Dave's explanation is legit, and is one of the main problems with the T3 rods.

[5NDIME]

Let me comment on why a clevis and mounting bracket is used on FutoFab’s Adjustable TC Rods, plus some recent improvements we’ve made.

 

We use a clevis to create a pivot point between the TC Rod and LCA. This allows the angle between two parts to change as the caster is adjusted. If the TC Rod to LCA connection were rigid, it will create a bending strain in the TC rod when any adjustment is made after installation. By having a pivot action at the clevis, no bending stress is placed on the TC Rod regardless of the final caster setting.

 

We have changed the clevis to a 5/8-18 LH thread for ease of adjustment. Our earlier design required a multi-step process if adjustments were significant. Now adjustments over the full range are done in one step. You unlock the jam nuts, rotate the link to adjust length and relock the jamb nuts.

 

So the pivot point is always loose?

[Dime Dave]

My adjustment description was more general than exact instructions. The pivot bolt should be snug during adjustment to allow some movement, but once the final suspension adjustment is done, it should be tightened like any other suspension fastener.

 

The thru bolt used in the clevis is a high strength 3/8"-24 AN spec bolt (76,000PSI shear strength). While it uses a self-locking JET nut and could be left semi-loose, it is always advised that the bolt be tightend.

 

The mounting holes in the clevis and bracket are of tight tolerance. The bolt has a grip length (area with no threads) sized so the mounting bracket bears directly on the full shoulder diameter of the bolt not on the threaded portion. This provides the most strength (16,000+ lbs in this application) and keeps the pivot play to a very minimal amount even when the bolt is partially loosened during adjustment.

[5NDIME]

My adjustment description was more general than exact instructions. The pivot bolt should be snug during adjustment to allow some movement, but once the final suspension adjustment is done, it should be tightened like any other suspension fastener.

 

The thru bolt used in the clevis is a high strength 3/8"-24 AN spec bolt (76,000PSI shear strength). While it uses a self-locking JET nut and could be left semi-loose, it is always advised that the bolt be tightend.

 

The mounting holes in the clevis and bracket are of tight tolerance. The bolt has a grip length (area with no threads) sized so the mounting bracket bears directly on the full shoulder diameter of the bolt not on the threaded portion. This provides the most strength (16,000+ lbs in this application) and keeps the pivot play to a very minimal amount even when the bolt is partially loosened during adjustment.

 

I think I see what you're saying. The ball joint at the front chassis pick up point is allowed to be dead center perpendicular on all planes from the fixed chassis point allowing complete articulation of the ball joint even if caster is adjusted because of the ability to pivot and set the angle of the pick up at the LCA? Making more sense now. So by adjsting the angle at the clevis when static ride height is adjusted/set, the front ball joint can be shifted around to be (what I would call) centered in the ball. Whereas with the T3 arm, that front point is what is and has less of a radius because it's not a ball joint, but just a rod end with limited rotation anyway. When you pull the lack of adjustability option at the LCA, it's limiting manipulation of the arm even more. I can see how the T3 might be stronger for rally or some very hard drifting and how yours is plenty sufficient for street/auto-x/track use. Now I know which way to go. Thanks Dave. As we say in North Mexico, your product es mucho bueno.

[Dime Dave]

The fact that you’re thinking about the reasoning is good, but the hard bolted connection of the T3 TC Rod at the LCA is where the problem lies and where our clevis improves on the design.

 

The real explanation is based in the laws of geometry when applied to a triangle. There are a couple rules that come into play. First, all the interior angles in a triangle will always add to 180 degrees. Second, if the length of any side of a triangle changes, it will change the angle at all corners of the triangle. The only way the sides of a triangle can change length and not change any angle at the corners is for all sides to change length in equal percentage (think of this as like using a zoom feature).

 

Now look at the chassis, LCA & TC Rod as being the three legs of a triangle. The chassis has a fixed length between the suspension pick-up points that cannot be adjusted, so any length change at the TC Rod and/or the LCA will create an angle change at the corners of the triangle.

 

So if you adjust the length of the TC Rod side of the triangle, then the corner angles will change to continue to add up to 180 degrees. If the angle between the TC Rod and LCA is fixed as with the T3 bolted connection, then the weakest side of the triangle will distort (most often the TC rod) because the LCA/TC rod angle will not distort as needed.

 

The T3 TC rod can be loosened at the LCA to allow the angle to change, but this will only move to the limits any over sizing of the mounting holes allow and may require further enlarging if the amount of adjustment desired is beyond those limits. FutoFab uses tight bolt hole tolerances in our suspension parts to properly utilize the bolts in a stronger shear condition rather than relying on the bolts for a weaker clamping force on oversized holes which could result in the parts slipping against each other and changing position.

 

Adjusting caster with the TC rod also creates another concern because it requires the angle at the LCA to chassis to change. If the LCA pivot bushing is a rigid material like Delrin or aluminum, moving the outer end of the LCA forward to add caster moves the bushings off its natural pivot axis causing it to bind. Polyurethane bushings are less suceptable, but at significant angles they too can bind. If you are making major caster changes I suggest the inner LCA pivot be either a stock rubber bushing or a rod end/monball as these are multi axis compliant and will not create a binding condition at the higher caster angles being used.

[flatcat19]

Good read.