Cliff Notes version:

Problem: Inability to get similar caster on one side; "floaty" feel

Solution: Bent lower control arm

Quick info that may be pertinent:

Car feels better, but nowhere near as good as it did last time on a track. The car seems "floaty" when hitting any bumps at speed. Turn-in is not crisp.

One of the problems encountered Tuesday was the inability to come anywhere close to 6.45 caster on the passenger front. Driver's side- no problem. They ended up getting the two sides even at... ... 4.5/4.4. Here are the specs we finished with for alignment:

I believe they came up with the toe specs based on me saying I felt that understeer was previously present. I might not be able to handle it; who knows. Now to the missing caster.

Is it possible, and to what degree, that removing/installing the sub-frame could reduce the amount of caster available to me? Could shifting the assembly give me some hope of reclaiming some? Is it more likely that some suspension parts may be undetectably bent? Is there a caster kit available?

As for the "floaty" feeling, is it possible that I over pre-loaded the springs? Am I too high(that doesn't sound right )?

I have an autocross on the 15th and the Dragon event the following week. May will be the soonest I will be able to hit a track. Obviously I'd like to get this squared away prior to the 15th.

Thank you for wading through this post. I tried to provide as much information as I thought was necessary to receive more than generic response.

 

Forgot to include the CW stuff. The car had half a tank of fuel, hardtop, me, and a couple of of items(maybe 5lbs). Wheels were street setup- 47lbs front(wheel/tire combo) each and the rears were 49lbs.

Before:

After:

 

Skip, I hope Race Miata or someone else equally knowledgable chimes in, because I think there may be more going on here than I can sort out. Inability to get the caster right would be my first concern, and I don't think I'd worry about anything else until that problem was isolated and eliminated. I would not install a caster kit (if one is available) until after I figured out what was keeping the caster out of spec. Since the problem is only seen on the side that was damaged I'm inclined to think that something is bent.

I'm probably way too paranoid, but I wouldn't track the car until the caster could be set properly, not because the caster is going to be a problem, but because I think the caster issue points to something else that might be more serious.

 

Two comments:

1) Most likely the right lower arm is bent why you can't get enough caster; happens often. Replace it with new or used part. Alternative could be that the rubber bushing at the rearward attachment and caster adjustment point is worn/torn (there's a thread by Windscreen about this), but I'dd bet that's it's a bent lower arm from the crash.
2) Measuring ride height to fender can be very erroneous, especially after a repair. Body panels can be way off but look even or straight. I believe the Helms say you should measure from the ground to suspension attachment point (tire wear and pressures should be equal also).

 

Because of the nature of in-wheel double wishbone suspension, it takes very little out of shape on either suspension arm to make camber or castor out of spec. I suggest taking a much closer look/measurement at potential bent parts. I don't have any experience on bent chassis but I would imagine and agree with Richard that the lower suspenion arm and bushings are the first to let go. The word "floaty" seems to confirm worn/broken suspension bushings. Even stock suspension should not feel floaty with some decent tires.

When I dropped my subframe for clutch replacement, alignment didn't change much. In fact, I desparately tried to get the most -ve left front camber by prying on the subframe to the left before tightening the bolts and I could barely increase left front camber just a bit. I doubt you would get the castor you want just by shifting the subframe, especially if limited castor setting happens only to the previously damaged side.

This may not be related but regarding corner-weighing, aim for equal front-to-rear ratios on both sides instead of equal cross weight. Your LF-LR ratio is 0.975 while your RF-RR ratio is 1.016. Try to get these 2 numbers as close to each other as possible.

 

Gentlemen, thank you for the responses. I'll look for my repair order from last year and see exactly what was replaced. I know several items where snapped off cleanly, but cannot remember which.

Tires have been KDW2's since the accident.

 

Skip,

I'll start by noting that I do not have as much race experience as the other guys or as much mechanical history with the car but my thoughts are............


First if there is a possibility of a bent part as mentioned above it would be wise to get that replaced.

Second---Castor. From what I understand it is the least important of the angles you are looking for up front. Camber leans the tire in so you have more contact patch through a turn. Toe controls turn in and sensitivity. Castor affects turn in and stability also but to a lesser degree. So I have my car aligned to the camber and toe that I want and where ever castor falls so be it. From my limited knowledge is that castor is the amount of leaning back of the front hub. If it stood straight up 0 degrees the car would be very twitchy (not good for sweeping turns but very good for autocross and sharp turns) and if leaned all the way back 6+degrees the steering would be very slow (think Nascar superspeedways).

I had my car aligned before the TCDesign front a arms and I asked the tech to give me the max negative camber and a certain toe and it didn't matter where the castor ended up. I got.

Front

Camber -1.6/-1.5 degrees
Castor 3.9/4.0 degrees
Toe 0.05/ 0.03 degrees

Rear

Camber -2.5/-2.2 degrees
Toe -0.06/ -0.05 degrees

So I wouldn't worry about the castor being 3.5-4 degrees. Like I said from what I know more straight up will give you more sensitive steering and more leaned back(+6) will give you less sensative.


What I don't get is the Toe you have listed. From what I have come to understand is negative is toe IN and positive is toe OUT. I think you want toe OUT on the front of the car and toe IN on the rear of the car. Toe OUT on the front will make the steering more sensative, toe IN on the front will cause the car to plow in a straight line.

I think the handling you are noticing has to do with the toe and not the caster.

 

John, thank you as well.

 

I had nearly identical issues with my front suspension, although the problem was on the driver's side. It was fixed by straightening the frame and the sub-frame on a machine and replacing the lower control arm.

I would replace the arm and see if you can get the settings to spec. If not, take your car to a body shop to have them measure the frame. It may not have been fixed the first time.

BTW, it is fairly easy to tell if your sub-frame is misaligned. There is a hole on the subframe that should match up with a hole on the frame. Check the helms manual for the location.

Finally, my understanding of caster differs from jfo. As I understand it, more caster means: a) more steering effort; b) more steering feel; c) better steering return to center; and d) more negative camber on the outside wheel as you add steering input. In the case of the S2000 competitively driven, these are all good things. That is why the UK spec caster setting goes up to 6.75* from 6*. I wasn't at all happy when my S only got 4* caster.

 

Yes, look for bent lower control arm (might not be visibly bent), and/or damaged bushing (see https://www.s2ki.com/forums/index.php?showtopic=165828 ).

Agree w/ teamking on caster. Think of it as "dynamic camber".