Setting up a C900 for the Track

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DeLorean
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Re: Setting up a C900 for the Track

Postby DeLorean » Tue Sep 16, 2014 12:04 am

Well.... These Hondas that keep beating us have ridiculous spring-rates, and at minimum 235 tires on 8" wide wheels, and a lot less weight. We probably need even more spring rate, and even wider tires to actually "handle like a honda" on asphalt. Radar speeds say a good running T5 C-900 gets way better straight line speed than a Civic with tricked out GSR motor, but they get demolished around corners and coming out of straights.

205's and 215's on a 6.5" wheel with any spring rate we can just go buy currently won't do. Custom springs with 600+ spring rate and 8.5-9" wheels w/rolled fenders I think is going to be what it takes to really get serious here.
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Jordan
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Re: Setting up a C900 for the Track

Postby Jordan » Tue Sep 16, 2014 11:16 am

We're running 225s on 15x7s. You could probably get away with more on an R-compound. I modified the lower spring perches to run 5" circle track springs that come in pretty much any rate you want. You are never going to out corner a lightweight civic, but you should be able to outrun them, which to me, is what makes racing fun.

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Re: Setting up a C900 for the Track

Postby DeLorean » Tue Sep 16, 2014 7:23 pm

Hmm. has anyone ever shoehorned some 245/40ZR15's on an 8.5" rim on a classic 900? Any chance without taking a saw to the car?
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Re: Setting up a C900 for the Track

Postby tirediron » Tue Sep 16, 2014 9:55 pm

the largest tire I have run is what Jordan is using. 225/45r15 on a 7" fox body mustang wheel. with much camber there is clearance issues on the lower spring mount in the front. these wheels have slightly more backspacing than a factory 6". easily solved using circle track springs and custom mounts. these tires rub my fender a bit in the back on full compression, and are already within a 1/4" of the control arms. I doubt any bigger is possible under stock sheet metal without sacrificing suspension geometry, or some pretty radical modification.
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Re: Setting up a C900 for the Track

Postby paulh » Wed Sep 17, 2014 9:00 am

http://rpglasfiber.com/?go=pro&hcat=729 ... at=2800774

Stock sheet metal isn't necessarily required in the class we run in.

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Re: Setting up a C900 for the Track

Postby DeLorean » Wed Sep 17, 2014 9:05 am

Hmmm, that would fix the clearance issues in the front anyway.
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Re: Setting up a C900 for the Track

Postby paulh » Wed Sep 17, 2014 9:16 am

They have rears too. Seems like it's about $1000 for the whole set front and rear.

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Re: Setting up a C900 for the Track

Postby DrewP » Wed Sep 17, 2014 1:13 pm

Can we talk about this photo some? Holy roll stiffness distribution, Batman... Brake lights are off here, I imagine this was just coming off hard braking, but that's way up there.

So the Lesjofors springs are too soft for serious race use, and do you have both stock ARB's? You made a comment on the previous page about it being tail happy, especially at high speed and especially over an upset in the pavement, which makes sense if the rear is stiff enough in roll to lift a rear wheel.

Carroll Smith has some really good examples of what is going on with the car when you're lifting a wheel and some ways to go about fixing it in "Tune to Win" I think.

It's probably in that spring rate calculator sheet, but how do those Lesjofors springs compare to for example the old purple Intrax springs or the red B&G's that used to be available? I have cut down Intrax springs in my yellow 99 and they are EXTREMELY stiff, no ARB's installed right now. I'll need to get some drive time in to see what needs changed.
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Re: Setting up a C900 for the Track

Postby tirediron » Wed Sep 17, 2014 1:57 pm

too big a rear bar in relation to the front will cause tire carry, not too soft.

in that picture, either a stiffer front spring or less rear sway bar would fix the issue.
-matt

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Re: Setting up a C900 for the Track

Postby DeLorean » Wed Sep 17, 2014 3:46 pm

I feel like it does not need less sway bar anywhere, more in the front maybe, sway is something it has a lot of as it is. In really hard cornering where you are in a side-slide it gets to having a sort of roll oscillation where the whole car feels like it's waving up and down sideways. If you give it a little brakes in that situation you can get the back end to step out a bit, a little counter-steer,and you get all 4 tires smoking, really scrubbing off speed fast. but the general tendency is to just plow if the car has taken a set and "settled"

I feel like on a track with race tires go-cart handling is what you want. "extremely stiff" is a relative term... The VW and the honda that beat us if you go to any corner of their car and push down, you can hardly freaking move the thing. I think they have more tire give than suspension give!

My suspension set up is

2 degrees negative camber in the front
stock roll bars front & rear
Lesjofors springs
Bilstein HD's standard valving - and probably a bit tired!
Hoosier A6's race tires

and this is too soft, I can say this for sure.
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Re: Setting up a C900 for the Track

Postby DrewP » Wed Sep 17, 2014 3:49 pm

tirediron wrote:too big a rear bar in relation to the front will cause tire carry, not too soft.

in that picture, either a stiffer front spring or less rear sway bar would fix the issue.




You're right of course, hadn't gotten enough coffee in me yet.
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DrewP
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Re: Setting up a C900 for the Track

Postby DrewP » Wed Sep 17, 2014 3:58 pm

That makes sense.

My car has more give in the tire than the suspension as well, similar situation. It's all a balancing act. If you can get the ride and roll stiffnesses where you want them without anti-roll bars that would be an ideal situation, but the geometry (especially of a road car) almost never allows that. The percentage of roll stiffness coming from the ride springs versus coming from the anti-roll bars is sort of a magic compromise that most of the suspension people I've talked to have pretty particular opinions about.

In any case - the jouncing around under hard cornering is probably lots of things all going on at once. Rubber suspension bushings, lateral spring rate in the tire, damping, and ride stiffness will all do that. The 'race' (or Sport or whatever B6) Bilsteins I put in the 99 are very very stiff under low speed damping like if you just lean your weight on them (like, they barely move, well under 0.25"/second just leaning on them) and soften up gradually at higher shaft speeds. Valving like that might be enough to cure your oscillation issue. If it's bouncing badly enough as is then the setup is under-damped already.

Good stuff. Autocross coming up out here in 2 weeks that I'm going to get the '85 to, will be interesting comparison. That car has:

-Koni red 3-positions @ soft/soft
-B&G springs
-205/55-15's on 6.5" wide Panasports
-Stock ARB's
- ~1.5* deg. negative front camber
-Basically no weight reduction other than A/C removal and sport seats
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Re: Setting up a C900 for the Track

Postby tirediron » Wed Sep 17, 2014 4:31 pm

a lot of it is personal preference, but when ride quality is not a concern i prefer to balance the car with spring rate alone rather than sway bars. i have very little body roll without sway bars, but i'm also using a pretty stout spring.

a stiffer spring resists roll entirely dependent on its rate, where a sway bar does so by transfering load to the inside spring. this can create wheelspin on the inside tire on corner exit with an open diff (front bar too big), along with carrying inside rear tire on entry (rear bar too big).

i'm no expert by any means, i have just tried a lot of things.

my RF camber is nearly -3.5 deg. RR is -1.5 deg.

my left side camber has no place on a road course. ;)
-matt

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Re: Setting up a C900 for the Track

Postby DeLorean » Wed Sep 17, 2014 4:59 pm

tirediron wrote:
where a sway bar does so by transfering load to the inside spring. this can create wheelspin on the inside tire on corner exit with an open diff (front bar too big), along with carrying inside rear tire on entry (rear bar too big).


I have all that going on. I think one of the first things I need to do is significantly stiffer springs and some proper shocks to match em.
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Re: Setting up a C900 for the Track

Postby jdwertz » Thu Sep 18, 2014 7:49 am

DeLorean wrote:
tirediron wrote:
where a sway bar does so by transfering load to the inside spring. this can create wheelspin on the inside tire on corner exit with an open diff (front bar too big), along with carrying inside rear tire on entry (rear bar too big).


I have all that going on. I think one of the first things I need to do is significantly stiffer springs and some proper shocks to match em.


I have never raced my c900 but I think the handling is pretty excellent. Here is my setup:

16x7 wheels with 205/45/16
Front - 1.5 neg degrees camber, Afco 500 lbs, Koni adj shocks, boxed control arms, Powerflex bushings, stock ARB
Rear - Landrum 650 lbs springs, Koni adj shocks, adjustable panhard, Powerflex bushings, stock ARB

We ought to meet up sometime soon and you can take my c900 out to get a feel for it. I think I need to go a little stiffer in the front and eventually add some bracing in the rear. Also the rear of my car sits too high so it is a little tail happy.


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