kene

iTrader: (2)

Since the BC Racing BR coil over cartridges/ inserts have pretty much the same dimensions across lexus/totyota model family (GS300,SC300,Supra,LS400, ES300, IS300) I thought to post this for those that may be interested (DIY'ers). As long as the BC racing cartridge's piston is 46mm in diameter the same can apply.

https://www.clublexus.com/forums/gs-...rts-1-3-a.html


PART 1: - The Mathematical Equations to derive your needed goals (natural freq., Motion ratios, etc)
PART 2: - Disassembly of the shock cartridge body
PART 3: - Re-Valving with Bilstein internal parts
BONUS PART: - Revalve/matching Ohlins sportline shocks damping ratios & Other shock manufacturer data graphs.

knguyenk

All your links are broken.

kene

iTrader: (2)

Sorry...it had been moved around by the mods.

Link is fixed above.

knguyenk

Very nice, I haven't read anything this detailed or technical in a while.

Gville350

iTrader: (10)

Man, I love this sort of thing! Great info; just won't be practical for 99.9% of us 2IS owners. If I did ALOT of suspension work on other vehicles AND had a shock dyno, I can see where this would be useful. For the rest of us, the $150 for a replacement cart is worth it.

Thanks for the details though!

kene

iTrader: (2)

But here is where the difference is. You can take your BC racing shocks and make then perform as equal or better than +$6,000 Ohlins, Motons, etc using the methods I have described in the tutorial.

The BC racing shocks in stock form are basically a linear shock. Even with a revalve from BC racing, the revalve is still a linear shock profile (see one of the last shock dynos...it is a BC racing, manufacturer revalved, 16kg/mm IS300 BC racing shock). Linear valving works pretty decent on perfectly flat race tracks, or courses. But with L.A. city streets there are all kinds of irregularities, potholes, dips and bumps. A linear valved shock is definitely not the best in these scenarios.

I was unsatisfied with how my suspension handled the city street and freeway bumps. I hated the slamming of the wheels on dips(harder clicker settings to prevent body roll), and the backaches when hitting big bumps at 75mph (14kg/mm front, and 12kg/mm rear spring[waaay to high natural frequency in rear] on 1st gen gs300). And the rear (under certain conditions) at this high of a spring rate with stock BC shocks would see a slight bit of air if I went over speed bumps at 8-10mph. It was a bucking bronco kind of feeling. I hated it. I was about to go to some softer springs I purchased, but then I thought to try and revalve them myself. I am glad I did. All that is needed now is to put the darn shocks on the car, and write a review of the of the results. After that I want to make a youtube tutorial from start to finish.


A digressive shock is the best option in the city/crappy street scenarios because it can allow for maximum damper forces in the low speed region for max body control and steering response. But blows off forces for high speed & high height bumps or dips from the road, which allows for a more comfortable cabin ride on rough streets. So basically the wheel can roll easily along the high speed bump or dip without transmitting this disturbace to the cabin of the car. A highly valved linear shock would skip over the bump, and slam down if the clicker is set high[rebound].


When the clicker is set or adjusted for maximum body roll/control, and steering response as priority, Linear can be like #3, and Digressive valving can be like #5, and at best #4. The green dotted line represents the car's interior cabin, and the blue dotted line represents the wheel/suspension.




"Well adjust the clicker to the softer setting!" you say......


1) With a linear shock, if I adjust the clicker to the softer setting, yes the bumps do not affect the ride anywhere near as much, but you end up losing some of the needed forces at the low shaft speed velocities which prevent body roll/ and body lean.

2) If you DO adjust to softer click settings and want to reduce the body roll, and braking dive you CAN go with stiffer springs at this soft click setting. But keep in mind, that by doing that you have just increased the frequency of the spring/system without having adequate damping force to match(soft click setting). So if you hit a decent sized bump, your car will bounce/oscillate up and down for a bit after the bump (example: a stock civic with cut springs to make it slammed).



Hence, why I wrote this tutorial on how to revlave your BC BR shocks to have the profile of a digressive valved shock. And not just any shock but one of the most world renowned manufacturers...Bilstein.
I modeled my tutorial around the Bilstein HD shock used on the supra as the TRD shock package, but truth be told the same exact procedure can yield the results of an Ohlin/Penske/Moton/AST shock and be even better than their off the shelf options depending on which shim arrangement/piston types you use. Once you get into the world of custom valving, the stigma of low level brands($500-$1,000) vs top level brands (+$5,000)can disappear.


For the shock dynos I paid a shock/race shop(FEAL suspensions) $65 to perform the dyno for me. This was for multiple clicks, otherwise it was $45 for just 1 click setting. This was done to verify my work and have a comparable baseline against the other 3 shocks corners I would end up revalving. Yes, southern california is expensive, but I have heard in other states they may charge as little as $25 per shock dyno. There are many off-road shops that also posses shock dynos.

The equations and math section (PART 1) is there to help those interested to get started on paper, and by the time they get to the assembly part they understand pretty well which key things to focus on in suspension design. Not just the notion of stiffer springs=better control.

The assembly section (PART 3) where I used bilstein parts and the bilstein valving manual is really a shortcut method which can be used to bypass the equations and mathematics portion. But the same valving manual and bilstein piston can also be used to assist in your mathematical calculations by showing you which shim arrangement will match your calculated forces at 20.5 inches/sec (Bilstein valving manual standard) shaft velocity speeds.

I must be doing something right, considering the Bilstein youtube video I posted that explained the difference between Linear vs Digressive valving, has been removed and that youtube account which had it closed down. I guess there are those out there who do not want the DIY masses to know how to do their own shock revalves.
From what I understand, shock design theory has been regarded as a "black magic" for the longest. I just want to give an option to those who have an interest in their own design.

There may be some that don't believe that you can achieve such acclaimed results as the top level brands. For those who don't believe, here is a post from a Miata message board that I found during the research phase of my project. The user "vg67gsr" once owned Ohlins, but bought BC racing coilovers, sold the Ohlins, revalved the BC BR's just like I am doing and said that they felt better than his off the shelf Ohlins. And he made a profit by selling the Ohlins. He even has 2 - highly sampled dyno graphs which show his 2 different BC racing revalve setups. Basically, the Ohlins felt great but the custom revalve gave him a bit more to be happy about. Here are the links below to his posts.

http://forum.miata.net/vb/showthread.php?t=488724
http://forum.miata.net/vb/showpost.p...69&postcount=4



Here he goes into detail about top tier brands vs revalved low end brands.

http://forum.miata.net/vb/showthread.php?t=519245
http://forum.miata.net/vb/showthread.php?t=500192


He even has a video of his revalved BC BR shock on the dyno.

WylieKylie

iTrader: (2)

I'm very interested to see how you like the re-valved shocks once you have driven on them.

For those that aren't as ambitious as you Fortune Auto sells reasonably priced digressive damped coilovers that seem to be reviewed well, although I haven't heard any reports in the IS world from anyone.

kene

iTrader: (2)

WylieKylie, If you only knew....I can't wait to install them. My car has been at the body/paint shop for a bit. I am eager to install the 2 fronts with a set of swift 10kg/mm springs(gives a natural frequency of ~1.38Hz) and write a nice review of the results. Then take the old fronts, revalve them, and put them in the rear with the 6kg/mm (gives a natural frequency of ~1.63Hz) swift springs that are on the car.

This is for an old '94 lexus GS300


-And I stand corrected the Miata forum's user "v67gsr" said his revalved BC BR's are way beyond his Ohlins.

scott1256c

Has anyone done the measurements for the 2G IS 350? I crawled under there today. These measurements are not super accurate, but they shouldn't be off by TOO much.
measurements in inches. A is the length of the control arm, B is the distance between the chassis mount point and the shock
-----------A------B
Front-----15-----10.5

Rear-----17.13---12.13

Using curb weight of 3527 lbs (ignoring driver) is about 1600 kg.
Motion ratio front 0.7, rear 0.71
weight dist 52% front, 48% rear

So following the rule of thumb that the natural frequency of the rear should be around 0.2 Hz higher than the front, we should be using springs that are stiffer in the REAR, whereas almost all coil sets I see are stiffer front.
Or have I done my math wrong??? Or did I screw up the measurements???

BTW, If you wanted a "sporty" suspension but still comfortable, springs of 10kg/mm front and 11kg/mm rear would give you a natural freq. of 1.71 front, 1.89 rear (FYI, changing to 12kg/mm rear would increase the frequency to 1.97). PROVIDED, OF COURSE that my measurements and math are correct!!

kene

iTrader: (2)

The 0.10Hz to 0.20Hz rule of thumb is a general rule. I have read online there are some aftermarket spring/coilover instances where this was not followed.

Think of it this way, the frequency is the rate of response to a disturbance in the system. Basically how quick or slow the undamped springs bounce per second when they hit a disturbance. If your front frequency is way too far off from your rear frequency, it can be like the difference between a plush comfortable ride in the front, and a quickly snappy, and responsive ride in the rear or vice versa.

This can feel like a bucking bronco effect when you hit a pot hole or go over a speed bump at 5mph. My initial BC custom spring rate of 14k-frnt/12k-rear on my 1gen GS300 felt like a bucking bronco and I hated that. I posted a somewhat detailed post about this when I first got the coilovers installed. That is what made me look at lowering the spring rates, and eventually decide to learn how to revalve my setup.

I feel that for the horrible streets of Los Angeles, a medium-low spring rate with a nicely re-valved shock profile will give the best(sporty, but with comfort in mind) suspension option for the average L.A. terrain.



With the information you posted, I calculated only the front and came up with the same 1.71 Hz that you found. So it looks like your math is correct. With my GS300 under the same 10kg/mm spring rate, a Motion Ratio of 0.604, and a front left corner weight of 480.8kg (1,060 lbs, driver included[200lb]) my natural frequency in the driver side corner would be 1.37 Hz.

To me this seems like a more comfort 1st, and sport 2nd based natural frequency selection, but keep in mind that dampers make a hug deal in how the car absorbs body lean, and road irregularities.


EDIT:
With the BC racing custom spring/revalve option of 14k-front and 12k-rear, my natural frequencies were 1.68Hz-front, and 2.32Hz from one of my very first suspension posts. I'm too lazy to verify if my results are spot on at his moment.



EDIT 2: Correction the front is 1.62Hz, and the rear is 2.13Hz with the BC racing 14k-F/12k-R springs with a 200 lb man..at that time[link below] I think I calculated with a 280lb man and I may not have been accurate with my math.


https://www.clublexus.com/forums/gs-...en-jzs147.html

amw896

this is awesome.

scott1256c

I had crawled under the car again a while ago to get better numbers.

front .... 14.5 .......11

rear .... 17.125 .... 11.75

so if I swap my 9kg/mm and 13kg/mm springs I get natural freq. of
front 1.76
rear 1.99

which actually isn't too far off.

... so I swapped my springs (and dampers) front to back.
I'll actually make a thread about it since it would kind of be hijacking this one to continue.

kene

iTrader: (2)

I dont mind If you post the information here, But even better would be to post a link leading to your newly created post here.
I dont consider it hijacking the thread at all.

Including the links on here(leading to your post) and on your new post(leading to here) would tie all of this info together for any future reader/member 5-10 years years from now.

scott1256c

good point. New thread is here.

kene

iTrader: (2)

Results have been posted, and I love it... I will be swapping from a 14K spring to a 10K spring on the front this weekend to see if it is even better. Remember, only the front have been installed. I plan to install the rears this weekend.