BC Racing coilovers damping adjustment recommendations

The rear feels softer than the front because the spring bucket is mounted pretty inboard relative to the wheel. So the forces seen by the wheel get multiplied by the distance to the spring. It's why the rear spring rate is higher even though there is much more weight on the front of our car. It's also why the rear seems to blow through the travel. 400lbs of force at the wheel probably equal 800lbs at the spring or more. So that's why a lot of people who track their Z's, G's, or any car with similar suspension design where the spring and shock are separate get "true" coilovers where the spring sits on the shock and it mounts outboard by the wheel. You can run lower spring rates and get better handling.

But since that's really not an option for us, basically our only solution is to run higher spring rates or more damping. Increasing damping has the negative side effect of changing both compression and rebound damping. So while I've maxed out the damping and it helps keep the car from rubbing/bottoming, it also slows down the rebound so much that if I hit a washboard, the car effectively has no suspension travel. Hopefully once I get the higher rate springs, I'll be able to crank down the damping a touch. As a disclaimer, I don't suggest people do what I'm doing. It is not good for performance, but it helps keep me from messing up my fenders and tires.
 
Well my fronts even on all the way soft, I still can't hardly budge by pushing down on the fender. Is that normal? Or shoud I reduce the preload? Again, right now I'm 5mm all the way around.
 
That would be normal since you have to overcome the weight of the car preloading the springs already. Only way to know is to drive it around in various conditions and adjust. I can't move my front or rear down either but it still blows through travel while driving.
 
What's a good dampening setting for street use. I want my ride to be smooth. Right now I'm bouncing all over the place in the rear I got it set up to 15 from hard front and rear . Am I doing something wrong. Clockwise is hard counter clockwise is soft correct.
 
15 is right in the middle. Turning it firmer, clockwise, will make it bounce less, but the ride will suck. I had mine set at full stiff to keep from bottoming and rubbing, but the ride was not good. I just swapped to stiffer springs which helped tremendously.

But short of that, increasing the preload will help on small bumps since your springs just wont respond until you hit a bump big enough to overcome preload. Increasing damping will slow down the travel but your car will feel like you're using a block of wood for suspension. Not much you can do, BC's are slightly undersprung from the factory.
 
Thanks for the help. Should I set It to 20 clockwise then. Also I heard anything above 16 is for track use. I'll gibe it some more preload then also due to the fact that I remove the purge and the passenger rear is making a loud banging sound which is weird cause the drivers side dont do it
 
The BC's aren't really a track coilover. Compression and rebound are adjusted at the same time which is not so great for race cars. Turning it up will make your car less bouncy, but it will also make your ride worse. Only you can determine what you can live with. Driving over washboard roads is horrible with the damping cranked up. I lived with it for a year, then finally decided to get higher rate springs.

If the passenger side is making a banging sound, check the preload. If you remove the perch, you have to adjust the preload to keep the spring compressed. Otherwise, it's just loose in the spring bucket. On the rear, shortening the shock body literally pulls the spring bucket up to compress the spring. Also, did you remove just the top locking perch or both of them? I removed the top collar but kept the lower one. The lower one keeps the spring seated a little, otherwise all you have is a tiny plastic ring.
 
Haha, thanks. Too much trial and error though, wish they had come set up better out of the box. I got them used, so can't complain too much. If I were to get new, I might have gotten the Kido's so I could select spring rate before purchase.

Funny thing is I haven't touched the KW coilovers on my BMW. I barely know where the adjustment knobs are, it's literally perfect and the primary reason that I realized the FX coilovers were riding terribly in comparison. The FX is getting there, the 14kg springs in the rear have made a huge difference. I turned the damping down a ton and it rides much better. Was going to swap the front springs tonight (12kg/mm vs. stock 8), but I got down to my car and found my floor jack broken. Idiot maintenance men "borrowed" it yesterday without my knowledge to move a rolling dumpster they broke. So now I have to get the concierge to pull the security footage from my space and argue with building management.
 
Hey, good information is good information! I miss the adjustibility of the BC rears but the heavier spring rates on the KIDO fronts are much better than the first CO set up I had. Sucks about your broken jack, I hope you can work something out.
 
Ok guys, I have a stupid question. As some of you know I have had a heck of a time getting my BC's dialed in (primarily the rears) anyway I have 10k springs in the front and 12k in the rears. I initially had 5mm preload all the way around but the front was way to hard so now I have 0 preload in the front and 5 in the rear. The fronts dampening is about in the middle, the rears are all the way hard and it's rides pretty good but I still get a little bounce in the rear.
Yesterday I had my car loaded with allot of stuff so the rear was weighed down quite a bit, it felt soooo much better with almost no bound. With that said, my question is as follows: does that mean I need to add more? Or less preload to the rears? Any help would be appreciated, thanks in advance!
 
Neither. Preload will not change this at all. It's a linear spring, so no matter how much preload you add, it will still compress at 12kg/mm. All preload does is keep the spring seated and to a lesser extent, change the dynamics of how the wheel rebounds since there is now stored force in the spring. When the car is static, the weight of the car overcomes any effect of preload, but if you were flying over bumps the wheel is lighter than the force of preload so there will be slight impact.
Put it this way, if you have a linear spring that has 5" of travel and you push it down 1", it will take the exact same amount of force to push it down the other 4". That's all preload is doing. Only on a progressive spring would preload make a difference in spring rate by pushing you deeper into the ramp up rate.

You want more rebound damping since that is what the heavy weight did. But that's not possible because it's not separately adjustable on BC's nor most street coilovers and you've already maxed out. I went with higher rate springs so it just won't compress as much.

I think the reason many of us feel the BC's are undersprung and bouncy is that most of us had H&R springs before. Those are progressive which means they ramp up the spring rate as you get deeper into the travel. OEM springs should be linear since the G35's are. It's probably why many of us felt that H&R's were better riding than OEM.
 
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So am I better off to go with a 14k spring, or put HR springs on the rear? I can't haul around a bunch of weight to make it ride the way I want :) What do you recommend I do?
 
Higher rate springs will help. They'll basically reduce the amount your suspsension moves and less compression means less rebound which means less bounce. It's like what you're doing by maxing out the damping but not slowing down the suspension travel like upping damping does. The downside is that your ride will be a little more harsh. But I find that my ride is less harsh with 14kg/mm springs and damping set in the middle than it was with 12kg/mm springs and maxed out damping.

I wouldn't get H&R springs in the rear. Mismatching suspension isn't a great idea. It's strange, most coilovers use linear springs, but most coilovers for Euro cars use progressive. My KW coilovers on the BMW are progressive and the ride is pretty nice. It's compliant at first, but it never bottoms out. Of course, separately adjustable compression and rebound damping help...it's also twice as much as BC so it should have all that.
 
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