Thoughts on BC Racing coilovers?

[LRegvall]

I'm suspecting that my dialing out the preload may have contributed to the freeway harshness I experienced. After researching preloading a bit, I began to realize that preloading helps increase compression travel. The harshness seems to have come from a lack of compression travel. Has anyone figured out, or have thoughts on, how much preload the BC BRs should have for "optimum" performance?

[IMPORTIMAGE]

yey for a quality review thread dedicated to leggy's!

[johnboi85]

i've had my bc's for 10k miles daily driven. its the kind of coilovers you'll have to get used to driving on everyday. great for competition but may be too stiff for others on the street. i love mine and wouldn't choose any other though.

[rubberman]

I just called BC Racing - NA and spoke with Tim about the rear ride height issues that I've been having on my wagon with the Enkei RS+M 18x8 (+45mm offset to fit Brembos) wheels & 225/40R18 tires. With 4 people or some load on the rear of the car, I am VERY close to rubbing the rear tires on the fender edge. Adding some spring preload widens the gap, but at the expense of travel and excessive spring stiffness.

 

Here's the solution - they do have a longer threaded cartridge body available that adds +1 inch to the standard Legacy rear coilover length (same valving, no difference other than length). Price was $95 each, so I went ahead and ordered replacements for the rear.

If anyone is interested in these, just call BC Racing tech support and speak with Tim.

 

http://www.bcracing-na.com/bccontact.html

 

I also asked about the recommended preload setting for the springs, they recommended this procedure: 1. lower spring perch down until the spring perch is just touching the spring 2. add 5mm of preload to the spring (YMMV on the final preload settings IMO).

 

+1 for BC Racing customer support so far. This should help my rear ride height issues since I wasn't after extreme lowering. I wanted to slightly lower things, but not at the expense of clearance / travel or having to roll the rear fenders unless I absolutely had to. The car still has to drive on dirt roads and in/out of gravel lots with moderate dips / holes when I go kayaking, so adequate suspension travel is also preferred.

 

Also, BC Racing offers rubber top mounts for the coilovers if anyone is interested in reducing the noise from the solid mounts (probably not widely known, but I think I've seen that option in one of Josh / ImportImageRacing ads).

[LRegvall]

I found that additional preload actually has helped my ride quality. I first encountered my freeway ride issues after I dialed out the preload. I have since added around 3/4" in the front and 1/2" in the back. I also softened the dampers a few clicks as well. The ride feels a little less harsh, more controlled and less on the bouncy side. I have yet to tackle the freeway locations that had given me problems before so I still need to see how well the preload worked for that issue. There is another thread on preload that suggests that the preload gives more bump travel. This seems to help the BC BRs. I may add more preload later to test the theory. I guess that's why adjustable coilovers were invented.

[kb2spn]

I installed my BC coilovers today and I am very happy.I had a sti(stolen)for four years and my cofidence in that car was high.I drove anywhere in any weather without problems.I had no confidence in the LGT,I was about to get rid of it but I decided to try the BC along with Perrin's 25mm front/rear sways.......well my confidence is back.

I did get the same ride height as the factory,the fronts could go even higher,front/rear is set to 15 clicks,FSB set to soft,RSB set to stiff,no alignment as yet but loving the ride.

[rubberman]

I installed my BC coilovers today and I am very happy.I had a sti(stolen)for four years and my cofidence in that car was high.I drove anywhere in any weather without problems.I had no confidence in the LGT,I was about to get rid of it but I decided to try the BC along with Perrin's 25mm front/rear sways.......well my confidence is back.

I did get the same ride height as the factory,the fronts could go even higher,front/rear is set to 15 clicks,FSB set to soft,RSB set to stiff,no alignment as yet but loving the ride.

 

Just checking, but did you set the max heights per the BC Racing specs? Front needs 80mm of threaded body still in the lower mount, rear needs 25mm. Only reason that I ask is no one else has been able to use those min specs and get stock ride height. For more info, see post #11 in this thread on page 1.

[LRegvall]

From what I can tell, the only way to get to stock ride height is to use their minimum specs and then add preload to raise the height. But that would be a fair bit of preload - maybe 1.75" front and 1.5" rear. BTW, what spring rates did you get?

[kb2spn]

I used the suggested minimum settings with the preload out of the box.The fronts were about .5 inch higher,I dont know what the factory ride height is,I am comparing it to the measurements I took before installing the BC.The car has 27000 miles,the height from the highest part of the fender to ground was 26.5 inches.

[IMPORTIMAGE]

I installed my BC coilovers today and I am very happy.I had a sti(stolen)for four years and my cofidence in that car was high.I drove anywhere in any weather without problems.I had no confidence in the LGT,I was about to get rid of it but I decided to try the BC along with Perrin's 25mm front/rear sways.......well my confidence is back.

I did get the same ride height as the factory,the fronts could go even higher,front/rear is set to 15 clicks,FSB set to soft,RSB set to stiff,no alignment as yet but loving the ride.

 

 

glad to hear it!

[robinlsb]

I have 20k on my BC/BRs (with Cobb F&R sways) with no problems. Sure they ride a little hard, and in the normal configuration the car is dropped about 1.5 inches or so.

 

And it is true that under certain circumstances the with above mods , you can get "launched" or get repeatable rebound.

 

But combine the above mods with a roll center kit , good rubber, and you will get a car that will handle better than most people can drive it.

[dschultz]

I used the suggested minimum settings with the preload out of the box.The fronts were about .5 inch higher,I dont know what the factory ride height is,I am comparing it to the measurements I took before installing the BC.The car has 27000 miles,the height from the highest part of the fender to ground was 26.5 inches.

 

Did you measure the ride height after driving around on them, or right after you installed them and lowered the car to the ground without a drive?

[LRegvall]

Good point. When they are dropped off the jack they bind a bit and don't settle all the way down. It makes the adjustment process a little more tedious because you can't just make the adjustments and measure. You need to move the car to get the height settled and measurable. Also, the more reliable measurement is the hub centerline to the arch. Using the ground allows tire inflation to affect the measurement.

[dschultz]

I installed BC-BR's on my OBXT and got this before and after. I lost more in the back and that's after setting the height adjustments to the max safe level.

Height  Before   After    Diff
RR      28.7500  26.4375  -2.3125
RF      29.1250  27.5000  -1.6250
LF      29.0000  27.3125  -1.6875
LR      29.1250  26.8125  -2.3125

I think I'll have to order the longer cartridges for the back. I also removed the rear helpers to get off the rubber as they were touching with nothing in the car.

 

Anyone with an OBXT remove the spacers in the rear sub-frame?

[dschultz]

I don't know what the factory ride height is.

 

I attached what I found for the MY2005 on factory wheel arch height.

[kb2spn]

after a few hundred miles over rugged roads,my fronts are 14.5" and rears are 14" and it does not make a difference if the measurements are taken from the ground as long as the tire pressure remain the same.

[LRegvall]

An update: I've put in 1" front preload, 3/8" rear preload. The ride height is 13.75" (hub center to arch) all around (if I actually found a flat surface). The front is more compliant with more bump travel. I don't detect any additional spring rate which makes sense but contradicts BC Racing's instructions. I do run the risk of reduced droop travel in the front (i.e., lifting the inside wheel in a turn) but this is mitigated by the fatter rear sway bar which helps keep the inside front wheel planted in a turn. I've got the front dampers at 19 clicks from full soft and the the rears at 6 from full soft. The car is handling pretty well - the rear softness helps smooth out things like speed bumps and the front stiffness stops bounciness. I haven't tested against high speed freeway crashing against pavement ridges and launches off of dips. The car still sticks like glue in corners in spite of having switched from summer BFG KDWs to all season Goodyear Eagle GTs.

[dschultz]

So I made some spacers for my OBXT to get the butt back up an inch. I posted my installation over at subaruoutback.org if you are interested.

http://subaruoutback.org/forums/showthread.php?s=&threadid=20640

I still have a little work to do, but for now all is well and I'm enjoying corners much much more than before :wink:

[IMPORTIMAGE]

wow, nice post up!

[LRegvall]

Another update: I've increased preload further. I have 1.5" in the front and .75" in the rear. There is no increase in spring rate that I can tell. That makes sense to me. There is a dramatic improvement in compliance and a decrease in harshness. It has allowed me (or required me) to soften the dampers. I am running the dampers around 14f/6r (from full soft). The car feels a whole lot better. The launch and crash problems have diminished with the increased preload. The preload seems to simply add bump compliance. I'm not sure I have experienced a downside to the preload and decreased droop travel which goes with the preload. If I disconnect my swaybars I could probably lift an inside wheel in a turn. But I'm not planning on doing that.

[dschultz]

I think what would really help set the preload is a sag specification for each vehicle or maybe by weight. Like when I setup my motorcycles. I measure the free length when the wheels are off the ground, then set it down and measure the suspension sag under its own weight. Then adjust the preload up or down to achieve a certain sag. I haven't searched yet, but maybe there is something out in the great "Internet reference book for mechanics". Increased prelaod will reduce suspension travel as you approach zero sag.

[LRegvall]

I think what would really help set the preload is a sag specification for each vehicle or maybe by weight. Like when I setup my motorcycles. I measure the free length when the wheels are off the ground, then set it down and measure the suspension sag under its own weight. Then adjust the preload up or down to achieve a certain sag. I haven't searched yet, but maybe there is something out in the great "Internet reference book for mechanics". Increased prelaod will reduce suspension travel as you approach zero sag.

 

I've tried to find a way to set it up more precisely but couldn't. One would think that it would be covered somewhere. There is another thread http://legacygt.com/forums/showthread.php?t=100565 that has a useful discussion of preload and that helped guide me. I couldn't find any good metrics for setting the preload though. That's why I did it experimentally, a little at a time. Each increase in preload improved compliance.

 

In theory as I understand it (discussed well in the other thread), there is a fixed amount of suspension travel. Sag uses up a portion of overall travel in the bump direction. Preload compensates for sag and changes the distribution between bump travel and droop travel, i.e., add 1.5" of bumptravel/preload and lose 1.5" of droop travel. The limits of preload are spring binding (when there isn't enough coil left to compress) or when too much droop is gone so that the tires leave the ground (like when I jacked up the rear and the front tire lifted off the ground). In theory, if you don't have much roll stiffness, you could lift the inside wheel in a turn.

 

I haven't found any limits at this point. It has just gotten progressively better. I'm going to run the current settings for a while to see what I find.

[LRegvall]

Epilogue: I've still got 1.5" of preload in the front and .75" in the rear. I've softened the front dampers to around 8 or 9 from full soft and the rears are at 6. I tightened the rear AVO 20mm sway bar and raised the rear end around .25". This has gotten rid of the understeer I was getting and the car rotates better than before those adjustments. Squat, dive and roll is virtually gone. There is no bounciness. And best of all, with the preload, the car feels very civilized even though firm. I don't feel like I'm compromising handling and comfort. Before adding the preload, I felt like I might have to switch to another set up.

 

The only negative with the coilovers at this point is the crash or bang sound when hitting sharp bumps or potholes. This is probably a reality of the pillowballs and not a function of the spring/shock. The good thing though is that it is usually just a sound. The crash doesn't jolt the car. I don't wince or tighten my grip on the wheel when I see dips or expansion joints on the freeway.

 

I may add some more preload (.25" - .5") just to see if I run into limits. But for now the BC BRs are working very well.

[dschultz]

My interpretation of the the BC-BR suspension from the last two months of driving is that these units are over dampened for street use even at full soft.

I find my car will fall into small impressions in the road pavement, most notable under 40mph. So the car dips in that corner rather than the shock extending into the dip and soaking it up. I have yet to add any preload to see it it makes a difference (more force on extension?).

When I compare to motorcycle suspension setup, because that's what I'm most familiar with...when you go with higher rate (stiffer) springs you need to open up the valves as the dampeners don't need to control the spring movement as much as a lower rate (soft) spring. What you want is the wheel to track the surface it's on to maintain traction.

So basically,

stiff spring & bigger valves, or

soft spring & smaller valves.

 

I'd be interested to know how these BRs would feel with 5/7kg springs and the same valving rather than the 6/8 they came with.

 

Or I'd like to open them up and see if the valves are modifiable. I haven't done any research on any forums about this, so I'll have to take some time to do that first.

[LRegvall]

I have the 5/7 springs instead of the 6/8s. Not sure how the additional spring rate would feel. Before adding the preload, I found that the BRs felt too bouncy when I softened the dampers. I had to firm up the dampers to keep the car from bouncing along irregular roads. I was at like 20f/15r. Then I started getting complaints from passengers ("ouch!"). That's when I started thinking about alternatives since I wasn't willing to stop for or veer away from bumps in the road and I wasn't willing to bounce around the rest of the time to accomodate them. The preload has changed the equation entirely. Now the dampers are 9f/6r and very comfortable yet controlled. It's an easy enough adjustment to be worth trying. Just make sure that you lower the car (i.e., drop the upper part of the coilover into the lower part) by a corresponding amount (e.g., 1.5" for 1.5").