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

Return them if you can. If not, resell and give Bilstein B14s a shot. I've ridden in cars with BC's and they are always bouncy, as are most other budget coilovers, especially those that come with tophats and lots of adjustment. B14s are the only coils with decent dampers under $1500 that I have experience with. That being said, I've heard a lot of people really like the ST coils, and any of the RCE options are bound to be good, since they are the suspension experts for this platform.

I have mine set at 8 clicks from soft in the front and 10 in the rear and they feel near stock, with the height no adjusted at all (preset height from the box), near as in still pretty damn stiff but comfortable enough for my girl and with the height no adjusted at all (preset height from the box). Need to re-adjust my endlinks.

In australia mca blues are 1500 so 1100usd? These usually beat out everything in Their market but shipping costs mean not to many people overseas can get them. Totally agree on palming the bcs off and getting something decent.

Shipping costs and no local serviceability/warranty. Hence world wide vendors with local dealerships may have extra edge for their offerings.

Yep. Here apart from the fact that any overseas offerings are no better thats why pretty much everyone runs mca's if they are serious.

I have this issue too, no matter what dampening setting I put, ride height nearly at max lowering. Even worse with someone else in the car. It's almost unbearable and gives me a headache, feeling my brain levitate inside my skull on EVERY SINGLE INDENTATION in the road. It's not like every 5 minutes or so, its literally every second of driving causes the bobble head effect. I'm going to be looking at better options around $2K range. I should have held off, but I really wanted the car lowered. Well, BC BR coilovers surely do their job at letting you lower your car, but goddamn it the tradeoff is not worth it to me. Have even contemplating going back to the stock struts... I have a friend who owns a 370Z that says to just get 12K or 14K springs, he has 14K, and it will fix the issue. But does it for my car?

You want low with a nice ride, quit f@3$in around and do it right with bags.

There. It's a coilover with zero development for just lowing and look nice while parked. .....Don't know why you didnt get teins since they are on 3rd generation of coils for 86s. you paid 1000 for something that's should be around 600.

Your friend has a different car with different suspension geometry. Do not try 12k or 14k springs.

This thread is a good example of what I talk about when I say that while some shocks are adjustable, there may not actually be 1 good setting in the 40 clicks they let you click. A lot more to it than "soft" and "stiff".

- Andrew

Forgive me if you tried this, but did you preload them correctly? It matters.

Was literally about to mention this, bouncy ride is often an issue with preload and is usually a sign that there isn't enough preload on the spring. Too much preload and the ride becomes stiff and jarring.

I recommend setting the shocks at the middle point of their adjustment range.

Standard preload for most shocks is to have the car in full droop and fully loosen the spring collar so the spring is completely loose, then spin it up until the springs are snug, then do ~3 more full rotations of the collar and then lock it up and you can adjust preload from there to preference. Still too bouncy? Tighten it up a turn. Too stiff? Loosen it a turn.

Once preload is where you want it, you can adjust ride height but do NOT adjust the spring collar for this on these coils. Instead loosen the lower collar on the shock and spin the entire shock in the shock body (I'm not certain this is the correct terminology so I hope what I'm saying makes sense) and you'll see the entire thing move up and down. Use this to set height as desired. Once set, get your alignment and you're done!

If you try adjusting preload and can't find something that works, contact BC and see what they have to say.

Yep. In simpler explanation, someone conveniently posted a video of the BC preload process in this thread.

This setting feels exactly the same as both extremes, 2 front/0 rear, or 30 front/28 rear. Dampening does almost nothing for my car.

Holey shit. I come back to this thread years later only to find people discussing preload as a way to change performance in this application. Preload adjusts rideheight here. Thanks for the laugh

That's why I bought your coilovers with the softer spring rates. Still loving them a year later

You certainly can adjust height via spring perch, but the BC's (and their multi-colored derivatives) are designed to move the suspension mounting point and leave the spring perch in a set place to adjust ride height.


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I won't argue about which is better, lots of ways to skin a cat.