macr88

I'm just curious about this and I'm sure it depends on how the shock is valved.
Wouldn't low speed be more or less for let's say smooth entry into a corner and med to high speed would be bumps and transitions through quicker transitions.
I always thought low speed rebound was ok to help control the chassis attitude but having too much med to high speed is what is the devil.
Or is it if one is over done then it's assumed the others follow and are over done as well?
I understand the transition point and that there will be that point where low speed will be active. Is it at that point that the issue occurs?

sorry for all the questions.

sirbunz

Incorrect, based on my conversations with Lee and his team, they tested and tuned the shocks for an S2000 in the Spring of 2007 at their Hebron, Ky location. I suggest calling Lee himself for the details. You are right that he was not the tech who developed them, but he was involved. He will be back in the office on Monday, April 5th. This info was also posted in the "Revalved KONI singles - report from A Stock" thread. There was a separate case where TC Kline developed shocks for the old T2 Car and Driver S2000 if that is confusing you.

captain_pants

+1 on wasting your time testing on old Hoosiers. Whatever you learn is completely and utterly non-transferable to new Hoosiers. Especially on an S2000 as it typically works the rears harder on AP1s. I've heard the fronts get worked a lot harder on AP2s. Maybe it's just my higher-than-needed-rear-slip-angle driving style that does in my rears so quickly. We swapped tires (that we thought were still good) front to rear and had an understeering pig on the test course at Nationals. Swapping on sticker tires completely fixed that. It just costs more to keep fresh tires under the car.

I struggled all last season with my Penskes (dynos in my thread linked above). After much fiddling with the knobs, we found that running on the softer side was better for this setup. But it was definitely a compromise. Going stiffer meant much better transitions but much worse handling over bumps. Going softer meant better handling over bumps but a seriously floppy-feeling car through transitions. Jason Collett was right on the money in that thread; by having to soften the settings for handling bumps we were seriously compromising the low-speed damping rates. The adjustments on Penskes primarily affect the low-speed damping, so needing to soften them to deal with bumps (high-speed events) kills your body control (low-speed) damping.

My shocks are at Stimola's to be revalved much softer so that I can run the adjustment knobs towards the stiffer end of the scale. When I originally ordered them I wanted valving similar to Wynveen's. Joe convinced me otherwise, that Steve's shock valving was very odd and that "anyone that got that setup hated it and asked him to revalve them". I now think that there's a healthy placebo effect for shock buyers, they want to really feel the extra stiffness that their money buys them. So much so that some will compromise lap times to get that feeling. Maybe I'm completely off-base but the standard Stimola S2000 valving was bordering on unusable for us on our bumpy lots.

FYI: We tested Jeff's and my cars (Nearly identical other than Penskes on mine and stock shocks on his) back to back at an autocross, swapping tires between the cars to eliminate that variable. We found that Jeff's car was MUCH easier to drive consistently and comfortably, and the times were completely similar. A 'good' run where we didn't make mistakes in my car matched an 'average' run in Jeff's car. So that Stimola valving was harder to drive than the stock setup but didn't achieve any additional speed. I wish we had done that test before Nats instead of after. Nationals was uber-frustrating, shame on us for not testing this sooner. We would have taken Jeff's car with the stock shocks instead of mine.

Another thing to consider for Stock cars: Bumpstops. If you run much more than critical rebound damping you are going to spend a majority of your time on your bumpstops. They're springs too, just highly non-linear ones. And they engage much earlier than you'd think. At our stiffer shock settings the car jacked down until the spring rate of the bumpstop was enough to keep the shock extending after each bump. It was a BRUTAL ride, much more harsh than my STS Miata with 500/325 spring rates. Driver and passenger were bouncing in the seats more than the suspension was moving.

While working a corner at Nats I was speaking to someone in A Sock that worked at AST. Sorry, can't recall his name. Paraphrasing from memory: He mentioned that they had to work surprisingly hard to make a shock that outperformed the stock ones. He felt that the stock S2000 shocks were better suited to autocross than any other stock shock he'd tested.

P.S. Joe Stimola passed away not that long ago. RIP. His son James is running Stimola Engineering now. http://www.joestimola.com

Forcednduckshn

I'm glad you verified this Mark. I'm not as intimate with the Koni engineers and I've never once spoken to Lee, but others have indicated this was the case. Thanks.

glagola1

You are describing why you need lowspeed compression. Rebound shouldn't be used to control the chassis if bumps are a problem. Some sites are smooth enough where rebound can be used effectively but this is fairly rare. This is the flaw in the conventional wisdom that rebound is where it's at.

It also illustrates why lowspeed rebound is bad. On the penskes the rebound adjustment is pretty much all in the lowspeed and the highspeed stays fairly unchanged. You said the shocks were working (keeping the tire in contact with the ground) when you/Jason removed the low speed. It's an illustration that the tire/wheel is getting held up by the lowspeed valving. Poo on that.

Macr88, does this clear up what you quoted me on?

sirbunz

Stuart Maxcy

sirbunz

Remember that the re-valved Koni Yellows you have an interest in are valved differently than the normal auto-x valving. Both the compression and rebounding were increased for the fronts.

I personally like high rebound and lower compression. In real word application, I feel this allows the car flexibility to move around, absorb the bumps, and hit those angles while keeping the car stable ... at least from the drivers seat. How that translates to technical terms, I don't know. It has allowed me to drive the car much faster IMO.

-Marc

glagola1

For reference, here is a dyno plot from my front shocks. The rears look similar. Rebound is on the bottom. I've been running the shocks at full compression and at click 3 out of 6 for rebound. Click 4 proved to be too stiff at the bumpy lot in Texas but was fine for the smooth lot in Dixie.

mavm86

Yeah, I was aware that the ones I'm interested in have more compression and rebound in the fronts. I was just wondering how the "standard" autox yellow valving compared to what some of the Penske guys were running. Either way I'm thinking the re-valved yellows will be an improvement over stock

bronxbomber252

I do not have a F/V plot of my shocks but I made a table using a Formula TheNick gave me It looks like i have a fair amount more low speed rebound stiffness at full still than Glagola and a little less high speed rebound.

These are on custom valved Koni Yellows valved byt Truechoice specifically for my STR setup though