B18C5-EH2

I've done a cursory search here, and didn't see any slam dunks answering my question.

I've got a 1994 Civic Si hatchback (2,300lbs. or so) for which I'm about to purchase BC Racing DS (digressive) coilovers. (<---clickable) Their standard rates are 10K/6K or 560F/336R. I was thinking of going custom rates (for which they re-valve the dampers to match for no extra charge) to have something more like 600/500, and then add a bigger rear bar for more rotation if desired. I'm currently on a stock GS-R 14mm rear bar, and GS-R front bar. I am 100% certain I will stiffen up the rear over the standard 336lb. springs though if only due to my kids riding back there sometimes, and I don't want the car to squat/rub, etc. They're only getting older, bigger, and heavier.

Do I stiffen up the rear by going with a stiffer spring rate, or leave it as-is and go with the 24mm rear ASR bar/brace combo?

My main usage for the car is street driving. Mixed highway, back roads, etc. 90% of the time I'm alone in my car, but for 10% my wife and kids might ride in it on the weekend. I'm used to having rear-biased rates on my old Civic hatch that I built waaay back when, and that car was also street mixed use, but also auto-Xing on the weekends. That car was 1990lbs. and was on 425R/550R rates with no front bar, and a 14mm rear bar. It rode "stiff" and rotated if desired.

Is there any sort of formula one can use to try and see how a rear spring rate vs. diameter of sway bar will affect the roll stiffness/rotation?

jdblock

My thought is to not run a bar with high spring rates. Keeping the suspension independent from each other helps for a street car that will see rough pavement.

The OEM install a sway to allow some cornering speed, but still run a softer spring. A sway is kinda a band-aid.

Now, if the bar is adjustable, and you're using it to set the attitude of the chassis for different racetracks, then you're going to have to do some R&D to find the sweet spot(s).

I actually have only the rear bar on, but I have it disconnected for the street. if I need more rotation at a track, I can easily connect it.

Kaan

iTrader: (3)

for a street car that might see an autox a couple of times a year... you want to go with the softer springs and bigger bars. this "ratio" you talk about it generally used for race/competition cars... which gets people into a ball park that they tailor for their driving style.

KoRn_vIRuZ

I have a spreadsheet with those calculations but unfortunately no time right now to dig them up. Kaan is right though, you want more bar and less spring on the street to improve ride comfort. More spring and less bar gives better response at the expense of comfort.

There is also a very interesting roll center correction kit from Honed in Australia that will reduce the need for stiff springs in back, yielding better ride comfort still. Don't know if anyone here has installed it yet.

Colin

iTrader: (1)

I've been following them on IG and am very interested to see some more reviews on their products. All their ads make the products seem well thought out and actually backed by R&D - but that's from a layman like myself, interested to see what a more pro or experienced racer/builder would say.

boxedfox

There is, yes. Take a look at this:
https://robrobinette.com/Suspension_Spreadsheet.htm

Just modify that spreadsheet to suit your car. You'll have to do a bit of work to measure motion ratios and calculate sway bar rates, but it's worth the effort. You can also get an idea of ride comfort by looking at the ride frequency numbers. If you can keep both front and rear under 0.9Hz, the ride will be pretty manageable on the street. Preference is to have a slightly higher frequency in the rear, the car will feel like it handles high bumps and low ruts better.