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Basic Drift Car Chassis Setup: The S-Chassis Tension Rod

by Nikita Rushmanov

 

The rear tension rod is probably the most overlooked suspension arm on an s-chassis. A lot of people don’t understand how it works, and there is a lot of conflicting information on the internet to add to the confusion. Because of this, when most people get adjustable arms for the rear of their car, they just set their tension rod to the same length as factory and leave it.

 

Today, we are going to show you how to properly set your tension rod. We will be making a very simple jig that will allow us to measure the toe curve of the rear suspension so that we can see the impact of our adjustments. Before reading this article, you should read our DIY String Alignment Guide to familiarize yourself with the alignment techniques we will be using.

 

The tension rod is the arm to the left.

The problem with leaving the tension rod set at factory length on a drift car, is that drift cars tend to run zero camber. In order to get zero camber, people typically lengthen the RUCA (Rear Upper Control Arm). This leaves you with a huge disparity between the RUCA and tension rod arcs, which gives you a very wacky toe curve. Essentially, the rear suspension will gain anywhere between ½” to 1” of toe out during the entire compression stroke (as the wheel goes up).

 

It’s pretty common to see drift cars run absurds amounts of rear toe, I’ve personally seen people run as much as 1” of toe in in the rear. People tend to do this when they have tension rods that are set too short, so they increase their static toe. That way when the car squats and toes out, it still maintains at least some toe in. This is the only way they can maintain any semblance of forward bite.

 

Today we will be working on Meliton Villamor’s 450hp 2jz pro-am drift car. The front end has Wisefab and the rear uses a stock knuckle and LCA with adjustable upper arms.

Meliton was very frustrated with his car. He told me that his rear end felt very lazy and unpredictable during transitions. He also described a weird phenomenon, where his car would only dive into a corner when he was off-throttle. After processing what he told me, I asked Meliton what his tension rod was set at. When he replied “stock”, it all made sense. I knew what we had to do.

 

Before we can start playing with the tension rod, it’s very important that we set the track width (if adjustable), ride height, camber and toe to the settings that we want first. All of those settings affect the position and sweep of the knuckle, which means that you will need to readjust your tension rod if you change them. You don’t really have to worry about it if you make small tweaks, but if you decide that stance is life and drop your car 4 inches and add 3 degrees of camber, you should definitely re-adjust the tension rod to make it work with the new settings.

 

We start by setting the camber to roughly the value we want, 0 degrees for this car. You don’t have to be overly precise when doing the first setup, since adjusting the tension rod will throw everything off anyway.
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Comments
SM_Clay72
SM_Clay72link
Monday, April 09, 2018 7:39 AM
how far from wheel center were you taking your measurements? The further out you are, the more toe in/out will be amplified in your measurements. Not a big deal if you are just looking for a 0 deg. stroke delta, but will matter for static measurement.
Rockwood
Rockwoodlink
Monday, April 09, 2018 9:58 AM
Looks smaller than the tire diameter.
Nikita Rushmanov
Nikita Rushmanovlink
Monday, April 09, 2018 5:45 PM
We measured the diameter of the wheel lip and drew lines on the plywood jig at the same distance. The toe measurements made on the jig are scaled exactly the same as the static measurements.
Crousti
Croustilink
Tuesday, April 10, 2018 1:52 AM
I found out the impact of the traction rod length when getting adjustable ones.

Went to a trackday with the rods set at the shortest. The car toed out like crazy as soon as i touched the brake, which made for very interesting yet slow entries. I just had to turn the steering wheel like 1° at the end of braking and voila, engage full opposite lock counter steer. No need to clutch kick, diff lock or hand brake.

Since i try not to drift but grip with that car, i investigated and found a simpler way to measure toe curve.

It requires a laser level, a bit of chalk (or pen, paper and tape), a heavy nut and a string. tie the heavy nut to a lug (if you have 5 lugs, so the top 2 lugs stay horizontal; otherwise tie it to the 2 lower lugs for the same reason).

-Set the laser level on the top 2 lugs, snuggly against the brake disc.
-if using pen/paper/tape, tape the paper in the wheel arch, the further you can from the laser.
-Move the suspension up & down. For each position you want, make sure the laser is horizontal (the knuckle moves backward when the suspension moves up, hence the heavy nut, it is supposed to keep it level), then mark where it hits with the chalk or pen and paper.

Do not forget to measure your "zero point" ...

Then adjust traction length as you see fit, and make sure its bushing or the RUCA bushing is not binding.
I like no toe change on braking and a slight toe in on full compression and could achieve it. Now the car really is easy, stable and predictable.

Basically i found that with the s13 subframe, you need to run too much rear camber if you want a good toe curve (otherwise you get binding the RUCA / tension rod bushings).
That problem amplifies with lowering too. Mine is not that low but i already have half a degree over best setting. Significantly better tyres would cure that, but at that point only slicks remain.

It also amplifies when replacing knuckle bushings with ball/rose joints, as they can move less than stock bushes.

It seems the S14 subframe makes the traction bush less prone to binding, so if someone needs that perfect setup and is allowed to, an S14 subframe fits with offset subframe bushes ...

Note: that toe curve change also happens at the front when lowering. Get some adjustable height outer tie rod ends for your steering rack to get rid of it (or just get better front knuckles)
Nikita Rushmanov
Nikita Rushmanovlink
Tuesday, April 10, 2018 2:04 AM
@Crousti

Yeah unfortunately with lowered drift cars and zero camber, 1/16"-1/8" of toe out under compression is as good as it's going to get with stock knuckle. The only way to get toe in under compression is with a PBM drop knuckle where you can move the toe rod mounting point on the knuckle.
Motary
Motarylink
Tuesday, April 10, 2018 4:04 AM
PBM knuckle is not the only way, GKtech knuckle has bump steer fixed from the get-go without afterthought extra unsprung mass and same for Wisefab rear setup that has elongated holes for a double shear mounted toe link.

I have 3D modeled the entire S13 front and rear suspension + S14 rear suspension via 3D scans and CMM measurements.

At higher higher ride heights the S14 subframe is beneficial with good anti-squat and bump steer, roll center migration and other values. S13 works better for traction on very low cars as the excessive anti-squat is reduced. Anti squat also reduced when lengthening the front upper link or traction arm / rear tension rod as the aftermarket has named it.

I would be happy to help people plot their geometries if needed @ motary at gmail.com for a small fee.

This article will sure help the novice out, nice write-up! To completely eliminate toe uncontrolled toe changes at the rear the lower control arm bushings need to be replaced with spherical bearings as they slide on their axis when loaded up.

Reference from NRR:

https://drive.google.com/file/d/0B4aIe4DAoIsUbG56NEdRSFlYbTA/view
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