Help needed BC BR Coilovers too bouncy 8k!
 

I have just purchased the BC BR Coilovers no extreme drop or upgraded Swit Springs. The spring rate is 8k and I have set to stiff all around but the drive is way too bouncy in the rear! I was considering getting Swift springs to kind of stiffen them up but I don't know how to shop for them I don't want to get the springs too small and it affects the height I am drastically because. I know they have shorter springs. I guess what I'm asking is should they be so bouncy in the rear? How do I go about shopping for swifts? I want to get the springs the same size they already are in the front and rear just higher spring rates. Can someone help? Thanks in advance!

How about you play with the damping. I'd do that first before looking at new springs.

If it's bouncing around, the springs are doing what they're supposed to.
The shocks need to be dialed in.

I have powered by max pro with swift springs 8k front, 6k rear. Set to full soft they bounce a bit because the dampers are set too soft and cant dampen effectively. Only had them on a week so letting them settle and whatnot. Im sure once i dial in a bit more rebound they will be fine.

Whats odd is for yours you say they are set to full firm? You sure? Maybe try setting full soft, drive on it for a couple days. Go from there. But for sure make adjustments before throwing money and parts at the problem.

Oh! Just realized, did you adjust pre load? Bc has a vid on thier site for doing that. I havent done it either and coul d be the reason for both of us.

How to adjust preload on a BC Racing BR...

https://vimeo.com/28427984

Soften the damping to see if it gets any better.
8kg/mm front and rear is quite heavy for the FR-S, so you may end up with a point where it is too stiff on harder setting, or it have a uncontrolled bounce on softer setting.

But work with the damping first, that is what it is there for.
If the don't work then I say a softer springs rate will help.

Jerrick

Um, how did you set them up (if at all)? It matters.

Softening is the wrong response.

A car that is bouncing is oscillating around the equilibrium point. That is, by definition, underdamped. A completely undamped spring would oscillate forever (assuming no friction, etc.). See graphs here: http://hyperphysics.phy-astr.gsu.edu/hbase/oscda.html

For your tuning goal, in general you want to reach critical damping (really hard to do, you're almost always on one side of the line) or every so slightly underdamped. To get there you need to increase damping.

If they're set up hard as a rock, the tire sidewalls may be the only suspension that is working.
Those don't have any dampening at all.

Have you ridden in a car with 100% critical damping? From what I hear it would be unbearable and from experience I would never even want to try it. Far North Racing suggests 65% and realizes that is likely too harsh for a road going car. Most passenger vehicles are set at 30%-35% of critical damping from the factory iirc which is probably what OP wants.

http://farnorthracing.com/autocross_secrets6.html

But yes, I concur that based solely on the short description it sounds underdamped and OP needs to go stiffer to control the bounce. But who knows maybe it's too stiff and he's bouncing from feeling every pebble in the road and relying on the tires as above.

:iono:

OP has turned the knob all the way in one direction and it doesn't work, time to try the other direction because the alternative is tossing out what he's got now.

I have driven an overdamped car, which is worse. The first problem is overdamped "feels" fast to the untrained butt. The second problem is that if your starting point sucks (like being seriously underdamped) then it's actually faster to be overdamped, even though it is not the optimal setup

You can dial in as much spring as you want. 8k is nothing. A friend of mine ran ~21k on the rear of the Celica (motion ratio not dissimilar to our rear BTW) and was successful with the car. As long as the damping is correct it won't be uncontrollably bouncy.

And actually I just spotted he's at full stiff. Yeah, time to go to a softer spring or throw that garbage out. If they sold it to you with 8k springs but not enough damping for them, it is truly garbage.

Yep.

Ok, I looked these up.

Yes, they come with 8k springs standard.

The shock adjusts compression and rebound together. This is generally not considered a good design (I'm being very charitable here), because there are two possible settings with these:
- compression is correct, and rebound is too low or high
- rebound is correct, and compression is too low or high

Furthermore, given the quality control issues with budget shocks, it's possible these have the wrong damping, or even that full stiff is softer than full soft (and yes, there are shocks out there that do this. So yes, you can try dialing out some shock and see what happens. I'd go in increments of 3 all the way to full soft (so 10 different settings to try) and select the setting that is least bouncy. If they all suck, well, you're probably out of luck, unless you can get them on a shock dyno to prove to BC that they suck and you should get your money back.

If you want a budget coilover, go for something without a knob. If you absolutely must have a knob, make sure it's either rebound-only or separate rebound and compression adjustment, or you're inviting extra trouble to the party.

You need to adjust your shocks. Cranking them all the way up to make them stiff is the bounciness that you are feeling. Bring them down to about half way and it should be a much better/less bouncy ride.

Upgrading to Swift Springs will make the ride even less stiff, so that sounds like a great option for you. Since at the same spring rate, Swift springs will feel softer.

To upgrade your BC Racing coilovers with Swift springs you will need to order these sizes. Then choose the spring rate you want. I wouldnt go above 12k all around on your current shocks, since above that they will need to be re-valved.

65mm-127mm-?k Front
65mm-152mm-?k Rear

http://www.kamispeed.com/Swift-65mm-.../swf.z65mm.htm