I meant camber. Sorry Im busy at work and posting from my phone. Thanks for answering my question.

 

Yup and that proves exactly what I've seen. Look at a go-kart. I don't have to prove myself to you or anyone here. Ya'll can bench race all you want, go out and try it on course. I'll let you know when you get the point of development that we had in the car in a couple years.

 

I've been running minimal caster for years through my own trial and error but not because of jacking effect.

 

I can agree with this.

I took my rear bar off before Nationals and liked it, but brought the bar with me anyway and installed it when I got out there. Bad move. Car was extremely difficult to throttle out of corners and I lacked a lot of confidence.

Took it off after Nationals and my confidence out of corners grew immensely. Indexing myself against my regular local competition, I knocked off 0.75 to 1 second on a 60 second course versus before Nationals. This is with no other changes.

I think the car still would like a rear sway bar, just much smaller than a stock CR rear bar.

There are always sacrifices somewhere in tuning the handling of a car. If I learned anything at all, it was better to sacrifice some speed in the slow sections(I had some slight slow corner push with no rear bar) rather than where you should be on the throttle and going balls out(corner exit).

I won't let stubbornness get the better of me next year, albeit in a different class though.

 

The bar on a CR accounts for ~385lb rate or 350lb/deg roll rate. If you liked the balance of the car without the rear bar, you would have needed add an equal amount of front bar to maintain similar balance. Assuming you liked a stock front bar and no rear bar, adding the rear bar would require going to a Gendron 1.25" hollow set to 5/6.

The point is, you can't just add a rear bar and expect it to work. Adding just a rear bar is a significant change to the car. It is like adding 250lb more spring to the rear.*

*Obviously bars and springs have different effects through a corner so this number is merely to make a point.

 

Speaking of roll rates--

Nick, it looks like you're running about 1400 lbs of spring roll rate (using wheel rates) and probably another 300 lbs or so from the front bar? I'm assuming that's to limit body roll to the <1.5 degree range or so (maybe more like 1.3 or less, assuming a ~12" moment arm)--is that because of rear bump toe issues? I'd think the camber curves are friendly enough on the S2K to not need the car locked down that much unless there are other issues.

Natural frequencies with those rates must be in the mid/upper 3s, too--maybe it's just for transitional response? Trying to wrap my head around rates that high on ~1.2g capable street tires.

I know I'm in the "other" camp now (MX-5) but I've been following your build long enough to know you don't do anything without a reason, so I'm curious.

btw: your wheels are one of my top 2 choices right now...hope to get back to you by year end if they're not sold yet. Just waiting on cash (hoping for a bonus this year).

 

I haven't gone through the roll rate calculations yet, but I can comment on the natural frequencies. The motion ratio is around 0.7, so the natural frequency with 900/850 lb/in spring rates is actually only 2.4-2.6 hz from memory of when I did those calculations.

 

Well, I eyeballed those frequencies, so I was a bit high, but figuring something like 650 lbs corner weight /70lbs unsprung, and 900/850 pound springs I work that out to about 3.21 Hz front, 2.94 Hz rear. Those weights are again, just guesses, but probably aren't terribly far off. Within +/- 0.2 Hz, I think.

So you're right, not quite as high as I thought. Well within the range of normalcy for an autocross car. Still, that much spring should really haul in body roll unless the roll centers are very low.

 

Maybe I should have clarified that I was running a custom Saner bar in front on full stiff, with 728 F, 612 R. The rear bar that I was taking on and off was the stock rear bar from my CR.

 

What are your camber and toe settings? That's not drastically different than my setup (spring balance and FSB, wise) and I'm considering leaving my '00 RSB attached and softening my modified Saner to eliminate some low-speed push.