I've talked to a couple local racers on this, and got some input from Scott (RR98ITR) but I also wanted to open it up to you guys...

The car is down at the mechanics for a new bushing set, valve adjustment and some other minor stuff. The plan is to get it in race trim within the next month and get an alignment. I figured while the cars apart I'd increase the spring rate on both the front and rear.

The car is on Tokico Illumina adjustable shocks with Eibach springs. The spring rates are 450f / 650r. I'd like to put the 650s in front and get a set or 900-950 for the rear.

Has anyone done this type of changes on their setup? Is any changes to the shocks needed? How will increasing spring rates effect the drivability of the car and what should I expect? What about rebound and dampening matching?

I have a call into Tokico and will be talking to Ground Control tomorrow. Any info that I need to get them and what questions should I be asking?

All experiences and advise are appreciated.... and Scott chime in if you see anything that you can help clarify.

Thanks
Greg

 

I've run as high as 500# with my old Illuminas and don't really recommend going any higher. I think they max out all they're worth at around 400#. If you're going with that high of spring rates on those shocks, you might actually make things worse rather than better.

John -- who thought Greg was on Koni's. Because, after all..... they are yellow.

 

I'm trying to understand how increasing spring rate will negatively effect the performance of the shock. I would think that stiffer springs would limit the travel of the shock (althought the travel would be more dynamic?) and therefore not factor into the equation as much as softer springs. I dunno...

Konis are yellow? Damn, I gotta get me some of those!

Greg - who should have listened and learned more at Berkeley. (oh wait, I was a Psychology major...)


[Modified by bulldog_RS20, 12:24 AM 7/16/2002]

 

ill repeat the west coast crx setup. 450f/900r on illuminas, st bars front and back. i am only missing the front bar. i think it works well for easily achieved oversteer. the front shocks need to be custom modified for dropping it in the fork for more shock travel. they tried konis, they did not like it. the philosophy was illuminas set to 5 all around, "set it and forget it" (ok, i added that) i've heard it worked for at least 3 seasons. and one other racer just got new shocks every season anyway, cost new is cheaper than a koni rebuild anyway. my experience is that after riding on the street, the shocks have diminished since i think the feel of car has changed subtly, but maybe my butt is getting used to it. they are far from "shot" tho. spend more money on Koni's if you wish. Tokicos have worked for the best lap times in my region and are working for me, but i got a lot more to worry about than shocks.

 

Tyson, let me ask you this: Was the shock originally fitted or matched for the #900 rear rate? Meaning is there a difference in shock rebound and dampening (sp) between say a #900 and a #650 shock setup?

The Illuminas are already on the car, so what I'm doing is replacing the 7" spring with the same except for the rate... for clarification, if needed. This also is a SCCA racecar, not streetable...

Thanks for the response...


[Modified by bulldog_RS20, 12:58 AM 7/16/2002]

 

From my understanding, a spring plus a shock is a damped spring. A damper slows the rate that the spring oscillates. If the damping rate isn't high enough for the spring rate, the spring oscillates longer which would make the car seem bouncy.

I am just basing this off of physics class though, I am not a racecar engineer

--buji

 

They are OTS (off the shelf) illuminas. bought em last year and put prokits on em at first and switched over to GC once I realized how much understeering I was when racing in competition (prokits worked GREAT when I did open track events and nipped 911 and NSX asses in the turns) . rear doesnt oscillate more than one half extra bounce, but it is stiff, as one should expect. set it on anything less than 5, yeah, im bouncing all over the place.

definately, theres a relationship with spring rate and shock rate. a specific spring rate requires a specific damping value to make a spring-mass system critically damped (where its not over damped or underdamped without dependence on input force) but im not sure if being critically damped for real world systems is 1) reasonably achievable 2) optimal. it seems tho empirically the illuminas were set right and the cost/benefit ratio was enough. but every driver and track is going to prefer something different. my real point? illuminas arent that bad and will work.

 

something to add in general. get on the track first and then find out what you need before you add stuff.

 

well, stock illuminas cant really hold that kind of rate. i had a set b4 and just run them with F5.4k/R4.4k rate. after 3-4 time trial events, its no good anymore(well, i mean it cant be same as new). the shock show more oscillate whenever i run over the big uneven road on freeway over 70mph(also lot of roll on corner) while i feel only one damping with my jic F12k/R6k when i go over the same spot with 90mph over. on top of that, illuminas is a twin tube design which is soften alot when it heat up(due to not enough oil capicity). another down side for it is that its a long stroke design(OEM lenght, right?), it might have problem when u lower the car alot. the shock might bottom out.

 

Wow! That's suprising to hear people are using that heavy of rates on off the shelf Illuminas. I believe you, but it's very suprising. I can't imagiane the shocks being very effective, but if it's working on the fast CRX's, so be it.

 

Sounds good.

 

I've been running 500/500 on my illuminas for awhile but I hardly ever drive the car except to and fro the track. I'll be putting 600's on the rear tomorrow evening b/c the are cheap and, well, I'm bored


[Modified by fastfour, 7:49 PM 7/16/2002]