kartaphilos

Hi all,

I sprint and hillclimb an S2000 in the UK that I bought earlier this year. I bought the car already modified and its been great except for a few rear grip issues with the car, particularly when really leaning on the tyre in a turn and it would let go quite quickly. I was wondering if I was getting some weird toe out issues when the suspension was getting compressed so I created a simple rig to give me some measurements (see below).

Result is that on compression I'm getting toe in at about a rate of 0.025 degrees/mm. This increases at the extreme ends of the scale. Also getting increased camber as the suspension compresses. Has anyone else done similar measurements on their suspension. If so, how do your results compare? FYI: My rear suspension mods that might affect geometry are bilstein coil-over (about 30mm drop), J's roll center correctors on bottom wishbone, and modified pickup point on lower wishbone (~10mm further inboard - don't know why this was done). I have standard tie-rod bars but do have some adjustables. What change in toe should I expect through the suspension travel?

BTW: Here's my setup which I think was quite cheap and hopefully reasonably accurate. I'm not sure I'd use this for setting absolute static settings but great for plotting change over suspension movement. Can anyone spot flaws with this approach?

I bought a cheap laser level from ebay, one with a cross hair feature and magnetic base. I had a spare disk that I put on the wheel studs which I mounted the laser level on to get the laser beam to clear the bodywork and aimed the beam toward a board placed vertically by the center of the front wheel hub. With the rear coilover removed the suspension could be jacked up and down and marks made on the board by the front wheel a various positions of suspension travel giving a set of crosses on the board. The horizontal movement indicates toe in or out (and angle calculated using wheelbase and simple trig). The angle of the cross hair shows camber change

Here's the pics
Laser level in foreground with board in the background


Marking board with plotted points and laser cross


Detail of the plotted points showing the line where the suspension is statically loaded


I guess if I can mount the laser on the wheel and figure out its offset from straight ahead at the front wheel I could set statically loaded toe. Camber would be easy enough to set by measuring the angle of the crosshair. What simple methods do you guys use to set geometry?

Cheers,
Matt

Garick

I'm not completely clear on your setup but it looks like you are plotting track width change more than toe change. I think you need a way to measure the angle directly.

blackey

Looks like you have it right to me. That seems right with the S2000. Toe out as the rear suspension decompresses, toe in with comression.

AKA toe out under heavy braking.


- The reason for the rear BSK.s

Antonov

Thats really cool, thanks for posting. How do you plan on curing your grip issues? On the AP2 Honda used a shorter upper control arm which increases the dynamic camber curve. That might be something worth looking @ on your 2000.

In regards to the BSK, what does it do for toe during compression?

bighead

Actually Honda lengthened the control arms in AP2's to help with rearend looseness when toe changes with compression ... something a bumpsteer kit can also fix with AP1's.

OP: Adding a BSK will reduce the amount of compression induced toe but without angle gauges you'll never really know by how much. You could compress the suspension while it's on the alignment rack to test it but it has been proven to greatly reduce bumpsteer

Antonov

Please tell me how lengthening a control arm (not sure which one you're referring) helps looseness? Also what does BSK have to do with dynamic camber?

I'm all ears.

bighead

he's talking about dynamic toe dude

Antonov

I understand that, I was suggesting adding dynamic camber in order to maintain more consistent contact patch...

I still don't see where Honda lengthened the control arms, maybe toe links, but not control arms...

bighead

Changes from AP1 to AP2: https://www.s2ki.com/forums/index.php?showtopic=483593

a BSK gives the ability to lengthen the toe arm and changes the pickup point on the knuckle.. It probably does nothing in terms of adding or reducing dynamic camber.

The original poster asked:

[QUOTE=kartaphilos,Sep 16 2008, 06:17 PM] I have standard tie-rod bars but do have some adjustables.

Antonov

I was suggesting a fix.... Where in my fist statement do I talk about dynamic toe except when I ask a question in regards to BSK's? Read slower next time maybe, I don't know...