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I disagree regarding going to higher spring rates with that valving on a commuter car. Yes, Spec Miata runs them, but only because they must because of the rules. And Spec Miatas make shitty street cars.
Get shorter bump stops or trim yours enough to allow good travel and get extended top hats to further assist with travel.
Since I'm on the mobile app, I can't scroll up to see what sway bar you are using, but a good aftermarket bar at least one inch in diameter will not affect your ride height negatively and will help to keep the car off of the bump stops in the curves.
So my next course of action is to order new springs and during disassembly take the spring out and find out how much bumpstop I really need to keep things from hitting each other. I should be aiming for about 3/4" shock travel before the bumpstop engages. If I cut the stops up to keep things from destroying each other and I still don't have enough travel in the suspension then I should look at ordering extended top hats?
Originally Posted by sixshooter
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Since I'm on the mobile app, I can't scroll up to see what sway bar you are using, but a good aftermarket bar at least one inch in diameter will not affect your ride height negatively and will help to keep the car off of the bump stops in the curves.
Yeah I'm still running a stock front and rear bar for now just because of funds available. My plan was to grab an FM front bar and 949 endlinks as a "mild" sway bar upgrade as my spring rates weren't crazy enough to warrant going huge front bar. I don't know if that actually makes any sense logically though.
No, you trim stops to prevent rubber to metal contact with either top hats. If you don't have 3/4" of shock travel at your ride height then you need to raise the car.
Continuing a discussion from the MCS shock thread (in Race Prep) in here so as to not keep bumping that thread (and understandably riling up the involved parties with commercial interests who probably don't want people mis-understanding comments about their products...).
Originally Posted by mekilljoydammit
Yeah, but specifying the high speed force of a digressive piston is pretty unhelpful. Ah well, Restackor to the rescue I suppose.
The high speed forces are determined by the cover plate (and to a lesser degree the support plate(s) that they bend back against). How much force it takes to open (digress) the cover plate is dependent on the cover plate shim(s) dimensions and the dimensions of the pre-load shim. The shape of the curve below the digression is the result of the bleed shim and the sizes of it's ports.
Here's a diagram I labeled of how the shims interact to produce the force vs velocity graph we're used to seeing:
And from some kind of bilstein manual I found (would love to find the original doc):
I'm pretty sure I could get pretty close to the right shim stack if I had a given curve I wanted (or at least could work with someone who actually revalves them to get there). Have been looking at ReStackor too - quite tempted to buy a copy.
So what I'm interested in is finding the desired curve for a base revalve for say 700/400 springs, a 2200-2500lb car, with digressive damping somewhere close to, say, in the middle of their adjustment range (or insert any other known quantity quality miata damper that has proven damping in there).
Allow me to be more clear - I understand which shims affect the nose and the knee of the graph. What I'm saying is that Bilstein's valving codes do not provide any obvious feedback on what you're getting for those values. A "300" linear stack will be producing 330 lbs of force at 10 in/sec (ish, I did a rule of thumb conversion) and, barring bleed and stuff, 165 lbs at 5 in/sec and so on - one number will tell you the whole theoretical FV curve. But a "190D" stack, that's not the case. I have a Bilstein digressive piston simulated in Restackor, but it's on my home PC so I can't really mess with it right now - it just annoys me a bit, especially since I haven't fully validated it.
Now. The problem I'm seeing in a lot of Miata dyno graphs is that most of the shocks aren't built with enough compression. Compromises though - without a base valve, you have to fight cavitation with gas pressure alone, and that has its own tradeoffs, especially with as short as the rear shocks are. It's interesting how much more gas pressure the ND shocks seem to be running based on dyno graphs I've seen of them - once geometry for those gets analyzed by someone I'd like to characterize them and figure out what's going on. In short though, some of the more "ideal" shock graphs (I'm not naming names, but you can do research) aren't doable on Bilsteins without either big gas pressure, base valves or canisters with base valves / compression adjusters. But there's some stuff out there that are built basically the same as Bilsteins (albeit with clickers) and have been track tested that should be a fair starting point.
And yeah I'm hinting around a lot and doing the secret squirrel thing when I could just be more specific. I know. We're blessed with vendors that are far more willing to put shock data out there than most and I don't want to be the dick who spills the beans on other people's intellectual property on an open forum to where any fool can take stuff to a circle track shop and undercut them. I might be willing to share some of my stuff when I get to that point - have to get the new version shock dyno built first though.
Great stuff you're sharing here, I'd like to get to the point that you're at but as I started investigating it became obvious that a dyno was needed as you've shown there just isn't enough documentation to be able to install pre-designed shim stacks. This is where I stalled out, I did take the time to see where the Hard S shock curves are in comparison to ideal critical dampening values and realized that the low speed valving isn't that far out for my particular springs.
I shelved the project at that point as there is lower lying fruit elsewhere to gather up first.....that and I'm winning with a setup that most on here would consider ridiculous.
Possibly because I'm crazy and have to do everything the hard way, I'm working on building a servovalve controlled pneumatic shock dyno - should be able to do a lot more than just stroke the shock in and out at a constant frequency. The old version worked surprisingly well - it just had a variable regulator to put the shock at various forces and a directional valve. So cycle the shock back and forth at one force, measure velocity, drop the pressure, repeat. It had limitations at low forces though (which are the most important!) and I really needed to clean up the output. One of the earlier raw outputs looked like this:
Allow me to be more clear - I understand which shims affect the nose and the knee of the graph. What I'm saying is that Bilstein's valving codes do not provide any obvious feedback on what you're getting for those values. A "300" linear stack will be producing 330 lbs of force at 10 in/sec (ish, I did a rule of thumb conversion) and, barring bleed and stuff, 165 lbs at 5 in/sec and so on - one number will tell you the whole theoretical FV curve. But a "190D" stack, that's not the case.
Yes I do understand your point. Bilstein names a digressive valving as say 300-100D but doesn't tell you about the choices they've made as to the low speed characteristics (i.e. the important part) in the name. In the stacks they list in the circle track manual online there doesn't seem to be any pattern/relation of the low speed shim choices to the naming.
I have a Bilstein digressive piston simulated in Restackor, but it's on my home PC so I can't really mess with it right now - it just annoys me a bit, especially since I haven't fully validated it.
I like the Ohlins X-Stack book (http://www.resuspension.com/assets/O...cks%20Book.pdf) because it shows a bunch of example shim stacks with different pistons and shows you what you get. And for that matter, I don't know that any of the off the shelf Bilstein stacks mess with ring shims.
I haven't seen that before, thanks for sharing. Something like that for bilstein would be very handy. We could just use an Ohlins piston but if you're going to that expense might as well choose a better starting shock or use one of the many good/cheap OTS options (i.e. XIDA).
I have actually seen that before - and did calculate critical damping values for some of the available options of Bilstein OTS/OEM miata options and posted them on another forum - will see if I can find that again as they were interesting (super over damped at 1IPS, dropping rapidly after that to way under-damped). I think it's useful to note that
Now. The problem I'm seeing in a lot of Miata dyno graphs is that most of the shocks aren't built with enough compression. Compromises though - without a base valve, you have to fight cavitation with gas pressure alone, and that has its own tradeoffs, especially with as short as the rear shocks are. It's interesting how much more gas pressure the ND shocks seem to be running based on dyno graphs I've seen of them - once geometry for those gets analyzed by someone I'd like to characterize them and figure out what's going on. In short though, some of the more "ideal" shock graphs (I'm not naming names, but you can do research) aren't doable on Bilsteins without either big gas pressure, base valves or canisters with base valves / compression adjusters. But there's some stuff out there that are built basically the same as Bilsteins (albeit with clickers) and have been track tested that should be a fair starting point.
I agree re: lack of compression - I was puzzled by the dynos for FM's new Fox shocks as they have so little. I think even with the short rears it's possible to get much better valving than the Bilstein OTS/OEM options for Miatas. I think the MCS/Xida compression curves/forces in the middle of their range are a good starting point and are doable.
And yeah I'm hinting around a lot and doing the secret squirrel thing when I could just be more specific. I know. We're blessed with vendors that are far more willing to put shock data out there than most and I don't want to be the dick who spills the beans on other people's intellectual property on an open forum to where any fool can take stuff to a circle track shop and undercut them. I might be willing to share some of my stuff when I get to that point - have to get the new version shock dyno built first though.
I've also seen people's shock dynos from certain Miata vendors who probably don't want them released and I don't think it would be good form to share those without their permission. But we can use the general principles and come up with our own valvings which is what I plan on doing.
Possibly because I'm crazy and have to do everything the hard way, I'm working on building a servovalve controlled pneumatic shock dyno - should be able to do a lot more than just stroke the shock in and out at a constant frequency. The old version worked surprisingly well - it just had a variable regulator to put the shock at various forces and a directional valve. So cycle the shock back and forth at one force, measure velocity, drop the pressure, repeat. It had limitations at low forces though (which are the most important!) and I really needed to clean up the output. One of the earlier raw outputs looked like this:
Here's the % critical damping vs piston speed in inch per sec I worked out for my car (IIRC used weight of ~2450lb) using the MSM bilstein & 600lb/in spring i'm running atm:
I actually was looking more at the published graphs for the DA Gen 1 Xidas than the SA ones - it was mentioned at some point that the Gen1 Xidas were only running a 40mm piston, so limited on compression. I like the MSM Bilstein's rebound side quite a bit, to be honest, but it could probably use more compression. Not that that's a theme for me or anything.
*quickedit* Oh yeah, and the first dyno was really kind of a hackjob effort - stuff I had laying around plus a few ebayed parts. I'll make a thread somewhere on the new one once my "fun stuff" budget recovers from buying an NA shell to turn into a race car.
Ok, so I now have in my possession a set of NA HD"s with less than 50 miles on them and a set of MSM"s off an 04 with 62k miles on them. Could you guys please explain in more simple terms how the valving reaction at high speed (one inch bump in the road?) and low speed (dip or undulation in the road?) would compare. I got that there is a hierarchy in the shock choices, I'm just trying to wrap my head around how they would feel and/or react on my car. 2000 SE full stock weight plus weight of turbo, exhaust, 04 MSM 17" stock wheels, (christ, are they heavy). Bought 600"s front 400's rear. I have yet to buy the RB front bar (1.25?). That's about it I think, Thanks, -JB
I hate to keep running set ups by you guys.... but I'm about to pull the trigger and don't wanna f it up. I have just found some NB yellow sport bilstein take offs. Plan is 90% daily driver, maybe 4 track days a year and some autocross. Car is stock, but will get a front sway bar (not sure which) and 15x9 wheels with 225 Ventus RS-3s. Shopping cart is as follows:
Allstar sleeves ALL64162 QTY4
Allstar nuts ALL64180 QTY4
Ride tech spring washers 70010828 QTY4
Energy suspension coil isolators 9-6103G QTY2 (pack of two)
QA1 7 inch 450 spring 7HT450 QTY2
QA1 7 inch 350 spring 7HT350 QTY2
I have honda bumpstops Ill cut to size, 30mm?
ISC 1.5" top hats for the rear, stock front.
Am I missing anything else? I want to make sure the list is complete, but that the spring rates will handle the larger sticky tire and be compliant for mainly daily driving with light track tossed in. My current stock showas are in good shape, i do enjoy the comfort, but I can't fit the tires I'm planning with stock shocks without rubbing. Any other ideas or suggestions to optimize this set up?
Depending on weather you use stock criclip location or not, what size of wheel and tires, possible contact between wheel and liner if your springs are not stiff enough. Again, I don't know this for a fact, but read in other coilover threads/sites. I'm about to do Bilstein build myself and most people told me to use stock hats in front and back, but I feel like adding 1" for a bit of extra travel may be a good idea.
Interesting. Ill have to go back through this thread again, I could have sworn going with ISC tops in the rear was the way to go... I would use shocks as they came off the car, same clip location.
Depending on weather you use stock criclip location or not, what size of wheel and tires, possible contact between wheel and liner if your springs are not stiff enough. Again, I don't know this for a fact, but read in other coilover threads/sites. I'm about to do Bilstein build myself and most people told me to use stock hats in front and back, but I feel like adding 1" for a bit of extra travel may be a good idea.
You're way out in left field here, the only way you'll have tire to hard part interference is if you don't take the time to cycle the suspension with the spring off and cut or shim your bump stops to maximize travel while preventing rubbing.
If you put NB shocks on a NA you'll find your rear bump stop ends up being less than 1/2" in height which makes for harsh engagement......add 1 1/2" top hats and you can now run a 2" bump stop that has a much softer engagement.
07-19-2016, 10:04 AM
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