freetors

I've been competing in my local SCCA region autocross (NEOKLA) with my s2000 for the last year or so and I feel like I've kind of hit a wall with my car setup/driving ability, or both. We run at two different lots that are composed of older asphalt. These lots are really bumpy with all the different asphalt seams. I feel like my car is a big handful to drive and it's hard to get the car to do what I want. It's like every time I hit a bump it wants to throw my car around. The course designers seem to frequently orient slaloms and other transitions right on the asphalt seams so you hit them frequently. I don't think my suspension is hitting the bump stops but I also can't prove that either. I think I'm giving up a lot of mechanical grip and predictability with my current spring rates. And my rates are much lower than the ones posted in all the other STR threads.

I know I have more driver skill left to improve but I'm finding it hard to improve myself with the car fighting me. For reference, at my last local event I was about 2.5 seconds behind an NA STR miata with the same tires (RS3's), mostly stock suspension, and a good driver. I was 3 seconds behind a BS AP1 s2k. He is pretty good and running RE-71R's. I took a ride with him on one of his runs and it was amazing how much more compliant and predictable the car felt over the bumps. I have beaten the guy in the miata on the same lot before so maybe one of us just had a better day than the other. I'm the only guy running an STR s2000 locally so I can't compare setups.

My autocross suspension woes are frustrating because my car handles amazingly well on smooth fast roads. Besides how bumpy it is, my biggest complaint with my current rates on course is how much understeer it has. It's like it doesn't want to turn at all.

My current setup:
AP1 '02
Fortune auto 500 coilovers with 12k/10k (672/560) springs f/r
stock '02 sway bars
enkei pf01ss wheels, 17x9 with 255/40 RS3 tires
alignment specs: 6.8* caster, -2.5* front camber, -2.7* rear, 1/16 total front toe out, 1/8 total rear toe in
ride height (ground to fender): 25-1/8 front, 25-1/4 rear
weight: 2729 lbs with a half tank, I've since removed 10-15 pounds since my last weighing with a different catback

I'm thinking about trying out some 550 lb/in springs on the front and perhaps 450s on the rear. Obviously I'm not trying to build a nationals level car but I would like to be able to consistently win my class locally and still be able to drive it comfortably on the street. I'd also like to get a lot closer to the BS s2000! I know I need to get some RE-71Rs but I'm still trying to maximize the potential of my current hankooks. And by the time they're worn out something else will be faster!

robinson

I've been down this road.

AP1 or 2?

Instability can be from not enough shock travel and hitting the bump stops, like you mention, but most glaring is your rear toe setting.

How low is your suspension? How much shock travel do you have? And how tall are your bump stops? These are vital questions that will help diagnose your specific issue.

One way to know if you are hitting the bump stops, is to use a ziptie around the shock shaft and see how high it gets pushed.

Dave

djsilverjohnson

Springs & shocks work together on compression and against each other on rebound. For that reason, when you increase spring rates, you need to decrease compression damping or the car will be skittish and unsettled over bumps. You also need to increase rebound so the shocks can control the spring or the car will "launch" over bumps.

afzan

A local here had 510's and the FA valving was not compliant enough over rough/bumpy surfaces , changing spring rates isn't going to fix that IMO

freetors

I don't know off the top of my head most of that stuff. I'd have to check my notes and make a few measurements. IIRC, I'm not that low compared to the setups posted in the STR thread. I believe it's 13-13.5" fender to hub center. My shocks have dust boots so it isn't very easy to get a look at the shafts. I want to say the bump stops were 1/2-3/4" thick. They seemed like a pretty soft foam from what I remember. It's been a year or two since I put them on. I'll get back to you with more concrete answers to you questions.

Regarding the rear toe, I tried 3/16" total rear toe for a little while, that's what I used the one time I beat miata guy, but I also had less camber at the time too. To be honest, I think it felt a little too stable, at least to me. Like just kind of sluggish. I've been wanting to get a real concrete measurement of my actual rear toe curve for a while now so I can see what it really does. I have not been satisfied with the info I've seen about this. I just haven't had the time or willpower to do it yet though.

I understand the mechanics of springs and dampers. These shocks are supposedly valved specifically for my current spring rates, and I'm considering moving to softer springs.

From what I understand of Fortune's lineup is that the 500s have much more "streetable", comfortable damping rates and the 510 series are more extreme and track focused. They describe the 500 as a coilover for the street and occasional tracking, and the 510 for track and occasional street. Personally, I sometimes feel they could use a little more low speed compression damping. But without adjustable compression damping or any kind of shock dyno info I can neither confirm or deny that.

devildust

What valving do the shocks have? I have same shocks FA500 with 16k/14k valving and 13k/12k springs. The shocks still suck over bumps unless you stiffen up the rebound adjuster, I think I run like 8 or 10 clicks from full stiff.

freetors

I did some measuring regarding shock travel bump stops and all that. The bump stops are 5/8" on both ends and are sort of a medium durometer rubber. All shocks have a 3" free travel, 3-5/8" if you consider the bump stop space.

Front:
ride height (fender to center of hub): 13-1/8"
total free travel: 4.5"
total travel w/ BS: 5.43"
droop travel: 1.5"
sag at shock: 1"
2" shock travel to BS from ride height
33% free travel sag

Rear:
ride height (fender to center of hub): 13-1/4"
total free travel: 4.89"
total travel w/ BS: 5.9"
droop travel: 2.25"
sag at shock: 1.38"
1.62" shock travel to BS from ride height
46% free travel sag

Considering how much travel I'm using up for droop in the rear, in addition to the softer rates, it looks like it might be wise to shorten the shock bodies in the rear and crank up the preload so I can maintain ride height and have more bump travel available. Unfortunately I have no way of knowing how much travel I'm actually using because of the dust boots. Also the bump stops are "free floating" and don't stay at the top like other shocks I've seen. I also noticed that my front fender liners are worn completely through to the metal on the inside.

freetors

They should be valved for these spring rates as I bought them new. I don't remember what I have them set at (somewhere in the middle of the range), they're turned up just enough to make them not bouncy. I actually think they're pretty comfortable over normal driving situations.

ConeKiller2

You are also not factoring sway bars. The hot ticket for any s2000 class that allows it is a bigger front bar. Karceptsb1.25 hollow is generally one of the standards and either no rear bar or a modified Miata bar. Although these can't fix the shocks they can improve the drivability and confidence in the car

freetors

Wouldn't that make it understeer even more than it already does?