Unbr3akable

Purpose:
Measure the rear bump steer for the OEM toe arm, and different shim configurations with a Megan Bump Steer Kit (BSK).

Setup:
Rear Ride Height: 5.5”, from pinch weld (14.5” from fender outer edge)
Camber: -2.7˚
2001 S2000 (AP1)
IZZE Laser Ride Height sensors for measuring toe difference (see picture)
Penny and Giles Linear Potentiometer for measuring damper travel / ride height (see picture)
MoTeC C127 data logger





Results (Toe):

Note: Suspension travel on track is between -1.5" (compression) to 1.0” (extension) for this setup; therefore, that is the range of interest for this study. In the plots, negative is bump and positive is extension/rebound, and negative is toe out and positive is toe in.

OEM TOE LINK:
Bump: 0.066” (0.155˚) TOE IN from 0-1”
Rebound: 0.088” (0.206˚) TOE OUT from 0-1”




MEGAN BSK, SMALL SHIM (5mm) TOP, LR:
Bump: 0.025” (0.058˚) TOE IN from 0-1”
Rebound: 0.035” (0.082˚) TOE OUT from 0-1”




MEGAN BSK, LARGE SHIM (10mm) TOP, LR:
Bump: 0.003” (0.006˚) TOE OUT from 0-1”
Rebound: 0.004” (0.010˚) TOE OUT from 0-1”



The amount of toe change with the OEM link is drastic, especially with larger suspension travel ranges (i.e., OEM dampers). However, toe in with compression and out with extension is a stable condition – as expected from Honda. The BSK, regardless of shimming, will make a significant reduction in toe change. However, you MUST tune each corner individually for best results. With the LR tuned, bump steer was reduced from 0.066” toe in to 0.003” toe out (bump, 1in.) and 0.088” toe out to 0.004” toe out (extension, 1in.).

Note, the optimal shims for the RR were found to be the OPPOSITE (pictures of curves attached below) of the LR; this likely has to do with the lobe (factory camber/toe bolt) settings. The point is to tune each corner individually; do not assume left = right.






Results (Motion Ratio):

I figured now was a good time to definitively measure the rear damper motion ratio. A laser is used to measure wheel travel (position coincides with center of rear axle). As shown, the motion ratio is 0.65 at this ride height with a slope of about 0.04 per inch (increasing with bump). This data is repeatable and not far off from what the community has found in the past. You can extrapolate your exact motion ratio at your ride height using this curve.



I will follow up with the front motion ratio in the future. Hope this helps.


Caleb

Scigheras

Great post and nice setup. Two questions:

- What year car is this? Just wondering if we are seeing stock pre or post facelift suspension design operation.

- You are saying you are running a different amount of shims between the left and right, and saying it's likely caused by lobe settings. What do you mean by this?

Unbr3akable

Good questions.

It's an AP1 (2001).

The rear toe/camber bolts (what I'm referring to as lobe settings) change the lower control arm pickup points on the chassis. Accordingly, there's a lot of interdependence on the positions of these bolts and it's influence on the toe curve. Another adjustment is the length of the toe arm. However, I played around with adjusting the toe/camber bolts and length of the toe arm, and in the end it was still optimal to run different shims left and right. It would be ideal if it was symmetrical but I'm not concerned with a 5mm difference in height; I consider this is within the tolerance of a production vehicle.

ncrx

Cool setup, how much did the Linear Pots set you back? Where did you source from?

Unbr3akable

The linear pots were around $250 each. I sourced them through MoTeC provided I have connections, but I highly recommend going directly to the source (Penny and Giles). You want the MLS130 for Motorsport applications: https://www.controldevices.group/PDF...20Brochure.pdf

circuitclub

They sell “lock out” toe plates to keep the eccentric bolts in the same position and force the toe arms to be adjusted via length rather than the bolts. It’s a great way to control for that variable, especially if you ask someone to do the alignment for you.

this is great info, thanks for sharing

would you be able to provide the eccentric bolt position and length of the toe arms for reference?

kos

Good data here. Thanks for sharing.

Unbr3akable

The suspension is currently being rebuilt for the upcoming season, but I will make a note to record the lengths and positions when it's back together.

Glad to share.

Caleb