08

Next, we strung up the car and set the toe to our desired setting, ⅛” toe in, in this case. We have a whole article on the techniques we use to set the toe and camber that you should read here.

 

Next we jacked up the car and carefully removed the wheel without knocking over the strings.

 

Our goal here is to measure the toe change across the entire travel of the suspension. This can’t be done with the wheel, because the wheel center will not be aligned with the strings as we move it up and down. We have to make a jig.

 

We decided to use this scrap piece of plywood I had laying around to make our jig. Any straight piece of sheet metal would also work.

 

We put some toothpaste on the wheel studs and pressed our sheet of plywood up against them to transfer the markings for our hole locations. We then drilled the holes for the wheel studs.
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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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