Mugenlude

We're looking at purchasing some new shocks, so I'm trying to run some calculations on the suspension to figure out where we should be with valving. Our car is buried in the trailer right now, so I would hoping to search the intro-net and find it, however, after 2 days of searching I'm coming up empty.

If anyone has weighed the suspension on a 1989 Civic Si, or has a link to someplace that references this information we would be appreciative.

I have wheels/tires I can weigh, but I'm looking for the UCA/LCA/Spindle/Rotor/etc. weigh. At this point anything would be better than a guess on my part (which I don't want to do).

Thanks,
-Jason

beanbag

Are you sure you know how to properly model the system?
How is the unsprung weight going to affect your choice of damping?
You can ignore the uca and lca mass.

Mugenlude

No, I don't know how to, although I'm trying to learn.

I don't understand how it all affects it, I just know what information people are asking me for. I'm trying to follow along with DG's dynamic calculator and the amount of unsprung weight effects what the shock curves look like.

Wouldn't I want to take 50% of the control arm mass?

vinuneuro

Unsprung mass is critical for compression damping.

Mugenlude

What shocks/springs we you using (alum vs steel)? I assume that was not including at wheel/tire correct.

VTECIntegra9

Half would be a decent approximation but their mass on our cars is going to be very small compared to the upright and brake and wheel package. If i were at home i'd weigh them but wont be for couple weeks now.

Someone please get this info! I would really like to know this also for my calculations

beanbag

Technically yes, actually, you will find the contribution to be pretty negligible.

There's a couple of points that I don't like about that calculator, but I won't bother to nitpick and instead say that it will get you in the ballpark on the rebound side.

Mugenlude

Yeah, it doesn't look like the unsprung mass changes the curve very much at all, but it still changes...

After plugging in all of the numbers it's interesting to see the recommended curves verses graphs of what some manufactures are using.

beanbag

That particular calculator sets the compression damping completely based on the unsprung weight, which IMHO is not right, but serves as some kind of lower bound on what it should be.

Egezzy

iTrader: (2)

nice responses to what i first quoted. my question would be..would that minute weight difference of say changing out control arms make a huge difference in the "proper" valving?

beanbag

no

Egezzy

iTrader: (2)

lol. exactly my thoughts.

beanbag

in what ways?

descartesfool

Bump kicks tire off the track. Amount of kick for a given bump and vehicle speed depends on unsprung mass, as the sprung mass doen't move much compared to the unsprung mass for a bump. Increasing compression damping slows tire's upward movement and helps keep the tire in contact with the tarmac longer. Suspension frequency for unsprung mass depends on the unsprung mass and wheel rate, and thus compression damping required to keep the tire in contact with the tarmac depends on the resonance frequency which depends on the unsprung mass. For low speed sprung mass motions on a smooth track, tires do not leave the tarmac and unsprung mass is less important.

beanbag

That's what one would normally assume, BUT:

What sets the damping ratio? For rebound, 65% is justified because it is the fastest return to equilibrium without significant overshoot. What is the justification for the compression side?

Why should there be a knee? The bigger the bump, the more the wheel goes flying, so why are you decreasing high speed damping?

Why is it that many drivers run significantly more compression damping than determined by this metric, e.g. the FCM Bilstein valving for Miatas, which have gobs of low speed compression? Koni, TC Kline, Moton, etc all run more compression damping than determined by DG's calculator.

Mugenlude

Thanks for the thoughts...

Is there another calculator out there that I should be looking at? In no way am I saying that the DG calculator is the end all, that is for sure, it is the only one that I have found and I know that other autocrossers have made mention of the calculator, so that is where I ended up.

Mugenlude

This comment would explain why the rebound graph for several of the manufacturers are similar

I don't know, that is what I'm trying to find out as this is the biggest variable from manufacture to manufacturer.

It would seem as if there are other factors involved besides just the graphs. For instance when I asked Koni if they could match the graphs of the Motons they stated that the car would be flying over high speed bumps, however, I know of cars on the Motons and they are doing nothing of the sort, in fact I would say just the opposite. That would leave me to believe that the parts used to assemble the shocks are working in a different manner.

I'm beginning to see why people call shocks design the black magic!

Mugenlude

BTW - these shocks will be for the autocross car, that may change the thinking...

A note on the original topic question... someone responded with 54 lbs for the front suspension (not including the wheel/tire), and 37 lbs for the rear (not including the wheel/tire). The unsprung masses listed above from PIC Performance were WITH the wheel/tire.

beanbag

I don't know of any that justifies its suggestions for compression damping.

Compression damping seems highly application dependent.


Compression damping is also pretty dependent on the type of shocks, e.g. twin tubes vs monotubes. If you were asking about the Koni Yellows, they are a twin tube design, and if you valve up the compression to look like the Motons (I'm not even sure you can), then the shocks will perform differently due to the acceleration dependence of the dyno plot. See the post #41 of this thread:
https://honda-tech.com/forums/showth...2374810&page=2

I have personally valved Bilsteins (monotube) to make the compression damping "look" the same as a Koni twin tube, and the shocks perform noticeably differently.

If you are asking about monotube koni's, I think if they valve them to look like Motons, they should perform similarly.

It changes the thinking a lot because autocross people often run sub-optimal damping to get around rules relating to spring rate and etc. You can ask that Solo-x guy what he thinks about autocross compression damping.

Compression damping is something I have not found a lot of info on the internet about. There are a bunch of people here with suspension books, so you can hope that they will share some info. I think one guideline is to run as much as you can in your particular application.

Mugenlude

Not looking for something to justify his findings, I'm saying I'm willing to look at other people's ideas.


We are currently run the Koni Yellows, when I contacted Koni it was in regards to the 28-series, so monotubes.

I have seen/read your posts on your revalving, I give you lots of credit for what you are doing! The fact that they perform differently supposes my thoughts even more, each shock has it's own characteristics even if they force/travel graphs look the same.


I'll have to contact Nate (Solo-X) and see if he can help me out...

I have also heard of the autocross crowd going in a slightly difference direction with valving. I believe that most of those applications are for Stock Category vehicles (I could be wrong) as they can't change spring rates and only the front sway bar.

We run in the Street Touring Class, which allows changing the spring rates and any sway bar. From what I have read (again it's subjective), autocrossers seem to like more low speed compression...

glagola1

They will not. Moton uses a 22mm shaft which displaces much more fluid. Also, they use very large gas chambers and little to no preload on the bump stack which makes the transition from slowspeed to highspeed very smooth.

beanbag

Actually, Koni monotubes, being non-external reservoir shocks, displace more fluid on the compression stroke because all that fluid runs past the piston. So Koni's displace stroke*(piston - shaft cross section) whereas Moton/JRZ only displace stroke* shaft cross section.
(Fluid also flows past the piston on ext reservoir shocks too, but it's typically as a bypass and no significant damping comes out of that.)

Also, I see no reason why Koni can't also use a low preload valve stack as well.

Anyway, I haven't put these two shocks side by sides, so I wouldn't know. I just say this based on my experience that every monotube shock I have dyno'd shows very little deviation from their ideal f-v behavior (e.g. very little acceleration dependence or hysteresis).

glagola1

I don't understand what you're saying. The only thing that displaces fluid is the shaft in any shock. Right?

beanbag

NO

If displaced fluid meant anything, it is the amount that has to flow thru valving to create damping force.

On an external reservoir adjustable shock, the compression valving is on the canister. The fluid that flows thru that is related to the shaft diameter.

On a "regular" monotube, the compression valving is on the piston. The fluid that flows thru that is related to how much fluid ends up on the other side of the piston. In this case, it's the piston cross section minus the shaft cross section.

glagola1

I think we're talking about two different things. You're talking about fluid that passes through the compression valving and I'm thinking about displaced fluid regardless of it's route through valving.

A shock has a set amount of fluid volume. It also has a gas chamber/reservoir. The space in the reservoir allows for the shaft to compress into the body. This is a fundamental design element that will mean a Koni monotube is never going to act like an external reservoir shock regardless of the valving. There simply isn't enough room in a monotube to run a large diameter shaft and package a large gas volume as well. There is just no replacement for displacement in this case.