SLAM IT BRO Large Roll Couples = bad4pussies High Roll Centers = INSIDE LIFT MORE BAD
 

Attention grabbing title aside, oh wait, if you clicked this because you're SLAMMED with your chrome negative offset dishes hellaflush'd and think camber is "aesthetic accenting" GET THE FUCK OUT, I want to keep this logical and am ideally looking for someone to analytically prove or disprove what I'm saying with deductive reasoning. Personal experience or even "my buddy's miata's lowered and it..." is welcome, since inductive logic is logic too or close enough. Just no: "I read on solomiata that it turns your miata into a 323 and the engineers at Mazda made the suspension geometry so good that it's designed and engineered to work with all spring rates and idk anything about suspensions but i know the miata is the best handling car ever and Jesus made it to protect me from terrorism..."

Ok so, yes, a larger roll couple with the same given centrifugal cornering force acting on the CoG (noting that centrifugal force on the CoG is not "real" and is a reactive/normal force "created" in response to the centripetal force being created from your steering input and tires) will create a stronger rotational force on the chassis and can lead to more chassis roll both of which will yield a lateral load transfer decreasing inner wheel normal force and increasing outer wheel normal force and since the coefficient of friction of a pneumatic tire has an inversely exponential relationship to normal force, the more lateral load transfer and resultant normal force imbalance the less total tractive force but that's obvious and intuitive.

WHAT ISN'T OBVIOUS AND INTUITIVE is the effect of jacking force from having a high roll center with the supposedly superior small roll couple. By vectoring the force created between the high roll center and center of the tire's contact patch, you can see there is a significant upward jacking force at the roll center which is shifted towards the inside wheel under roll. Apparently, jacking force is far worse than the roll couple though.

What seems to be the case is that on a stock vehicle designed to be sold as a fun sporty practical convertible with comfortable spring rates (as the engineers at Mazda intended), a small roll couple providing little leverage for body roll to compress those comfortable springs and I'm assuming a suspension geometry which keeps the roll center relatively centralized and thus minimalizes the effect of the jacking force on body roll is perhaps "Mazda's secret suspension magic"

The effects of a low CoG are clear though, and body roll from a large roll couple is easily combated with heavier springs and anti-roll bars. I feel confident the effect of the lower CoG and reduction of jacking force are superior to the stock suspension as long as you have enough anti-roll from spring rate and/or bar to prevent the chassis roll from growing enough to increase the lateral load transfer.

There was a thread on here that had suspension geometry data in it but I could neither locate it via the forum search or even google: ______ site:miataturbo.net Anyway, if someone has that or useful criticism please reply! Or suspension software recommendations! I'm going to start doing some analyzing with this (http://www.susprog.com/susptype.htm), seems good right? I gotta stop Google binging though (lol@ binge becoming bing...) and finish up my 4130 and rod end order at chassisshop.com. I've got a AC/pulsed DC inverter TIG with dual IGBT H-bridges for an "advanced squarewave" output (wse200p: pride of china lol), a '90 NA subframe still bolted to a completely bare engine bay, a '99 subframe right behind me, a JD2 Model 3 bender and TN-100 tubing notcher on their way from a neighboring state, and only like 4 hours of sleep in the past 48 hours.... Any good suspension geometry advice will be fabricated into reality! Gaah, so much saving and researching, so close to duh ultimate myahta dream supercar :drool: Boy I tell you gotdamn? what the baby-snatchin tornado that I cannut wait to start jiggin and TIG'n YEEEEHAAWWWW.

wat.

wat. wat.

Woah crazy post. Make sure to do practice bends with that bender it takes a couple times to figure out the exact dimensions that you get out of the bender.

What the FUCK are you asking!?

Yes a higher ride height gives you reduced body roll but greater weight transfer on the outer tires and increased jacking, and yes you can counteract the body roll of a lower ride height with stiffer bars / springs, but very high spring rates reduce grip on bumps. Less of an issue on the track, more on back roads.

In practice... look at emilio's recommendadions...

haha, I promise it's all sound reasoning. I should probably tone down the "self-aware insanity" dialect. I hadn't opened up my copy of Tune To Win (by Carroll Smith) since like 11th grade, which was only 3 years ago lol. I guess I got kind of excited and rant-y since physics is a lot more natural/embedded in my mind now so I really understood the suspension geometry concepts and even picked out a trig error in there ha. (It's a kinda dated book, very apparent how "pre-computing-age" it is, but not bad for the $10-20 it cost) I might post up some graphs showing what I'm talking about. But lyk, rite now, I'm stuck in this insomnia bullshit, tryna get mah blunt fat so I can sleep aayyyyee. #winning

I'm talking about the roll center though. Keep in mind I'm fabbin' a new subframe and linkages so I have some freedom here. Some of the original post was me being angry with people that are against lowering because they don't drive well enough to deal with the more responsive large roll couple and don't have their spring rates and bars right. You can fix the tire compliance issues with progressive spring rates though. Before they repaved Road Atlanta, that shit was waayy bumpier than most backroads even.

haha, sorry I get bad at compressing my thoughts when I haven't slept which is usually, lately at least..., when I find the time to get on this forum...

My main argument/statement: Although in the static position it transfers more lateral load to the outside wheel, a large roll couple with a lower roll center is better (especially with a lowered CoG) because you can control and minimize your roll angle with bars&springs. You can't stop the jacking force from a high roll center (stock geometry) though.

The "relative magnitude" of these forces depends a lot on CoG though. As would be pertinent in a formula car book (Tune To Win), a low Cog is much less sensitive to a low roll center because the resultant roll couple is still relatively small and you have very large cornering forces which will cause the jacking force to become more apparent.

I just figured I'd throw a post on here and see what people had to say because I have a lot of other stuff to get done before I measure all the suspension geometry and sit down and figure out how to use the suspension software (my bad on the ranty lack of organization)

Also, the stock geometry seems to have some kind of "worship for the unknown" as if Mazda divinely created it when in reality I think they just did a damn good job designing a linkage that works well with low practical springrates, and coupled with the miata's innate chassis characteristic of being a little light relatively low CoG car the suspension might receive some slightly unwarranted "respect".

I see exactly where your coming from and where your going with this.

I agree that the torsion effect that leads to jacking is bad, and gets worse the more we lower our cars, and we all know that lower is better even though it increases these torsional and therefor jacking forces.

If you stick to the same design as stock, but manage to move both front and rear suspension pickups vertically straight up as much as you want the car lowered you will be onto a winner.
However be sure not so affect your steering geometry too much by moving suspension pickups relative to the steering rack. IE move the rack too.

Also while your at it it couldnt hurt to move the rear top arms pickup point a little further inward and make the arms 75% of that move longer. Allowing less rear camber change on compression helping grip exiting corners.

Dann

Dann

More camber = better handling

/thread

Was that a response to what I said or just your response to the whole thread?
Sorry, couldnt work it out.

Dann

Get some sleep.

+99

Come back, slow down, speak in layman's terms, and give us some diagrams/graphs.

The only thing I noticed in that first post was JACKING FORCE

Why not work on the spindle side?

I agree with moving the stock points up/ mazda did this when they came out with the NB. I don't know how much would be Ideal, that would take a lot of math. To much and you may loose performance, you also may find it to be a pita because even though you are making your own sub frame, there is just not that much room to move the upper mounts. For this reason I figured custom spindels to be a better option. Sorry for the spelling My cell phone sucks to type on.

tl;dr

I think he's saying.... we all need AST's, 15x10s, and 275 ho-hos on our cars...... :-D

By lowering, we are lowering the roll center which is the point the chassis rolls about which is determined by the suspension geometry. We are of course also lowering the CoG relative to the ground.

Not quite, you have the CoG and the roll center which basically work like a lever (centrifugal force acts on CoG and pivots about roll center) in causing chassis roll and some "resultant" (weird bcuz centrifugal isnt real) lateral load transfer. There's also the torque arm of cornering force * CoG height = lateral load transfer * half of the track width. Jacking force however is determined by the tractive force at the tire. The tractive force at the tire is generating an inward force which acts through the roll center, the angle of said force is determined by the roll center height and distance from the center of the tire's contact patch. By vectoring out the components forces of this angled force, you find the horizontal component to be the centripetal force and the vertical component to be a jacking force acting to raise the inside of the vehicle. The lower your CoG, and the more anti-roll you have, the less effect the large roll couple will have and the more apparent the jacking force becomes. The exact forces require evaluating the geometry, CoG , anti-roll forces and vehicle weight to determine how to achieve maximum tractive force which is a product of minimizing the cumulative lateral load transfer influence by all of the above forces. Tire compliance can suffer from aggressive springs and bars but may be regained with the use of progressive spring rates, effective tuning of the rebound and damper. Also, I reckon plain ole drivin good and smooth helps too.

I'll post a new thread once I get all the numbers n stuff. It should have diagrams, more clarity, and less insanity :D

What the fuck does the Tenderloin District have to do with suspension geometry?

The amount of weight transfer to the outer wheels is a function of CG height and not roll center nor roll couple.

An increased roll couple increases body roll but does not increase weight transfer on the tires. The increased roll couple merely has more of the weight trasnfer through the springs and sways (elastic) and less through the linkages (inelastic). This of course assumes a constant CG height.

But yes I'm with you; the car works well pretty low and stiff... at the track (fewer bumps than backroads), based on 949's experience.

In general the only bad thing about a high roll center is the jacking force. Note that the bad effect of the jacking force, which is raising the CG while in the corners, is *reduced* by stiffer springs.

Oops, sorry, there was a point when I thought the torque arm was cornering force*roll couple = load transfer * distance from tire contact center to roll center, so I slip that in there mistakenly sometimes. The chassis roll from the larger roll couple increases the CoG height and moves it outward a little, so I guess the "dynamic position" is what I should've put for stating the increased lateral load transfer due to larger roll couple.

I think low and stiff (not as low and stiff as for the track) with progressive or the sort of "dual rate" springs would work well for the street though. I'm dropping my CoG a fair amount by means other than just lowering (we'll see how much) and I think that along with the stiffer spring and anti-roll may work better with different geometry. I can't wait too look at all of it in a suspension design program, still didn't get to measuring anything today though...

The problem with soft springs + progressive bumpstops is this.
They get stiffer with compression, so in cornering, the outside springs don't compress as far, but the inside lifts more than if you had stiffer linear springs. The latter raises CG and worsens the tire camber angle vs. the road surface, while the inside reduction in compression, doesn't improve it, due to the car's camber curves...

Nick,

What are you trying to achieve with all of this? Are you racing?

Jason alluded to it, but have you thought about your force based body motions? Kinematics only analysis isn't 100% valid if you have asymmetries and non-linearities (ie bump stop engagement, comp/rebound damping balance, progressive spring rates, which is never the case).

Like you said, jacking depends on the tractive effort of the tire, so I think a good analysis should look at the instant centers of the outside and inside wheel along with their lateral forces. The inside wheel is trying to pull the sprung mass down and outside is pushing it up for the Miata (RC above ground). If you can reduce lateral load transfer, thus increasing the pull down effect of the inside wheel and reducing the push up effect of the outside wheel, you will have less total jacking. Also, since most dampers for the Miata are rebound heavy, you will have a slight jacking down effect with roll velocity.

JasonC SBB -- What's your logic on your statement of "increased ride height = reduced body roll"?

Higher ride height = smaller roll couple = less body roll

Would a dual spring setup, like on the XIDA coilovers, fix that?

You know how I know you're gay...

You know why people hate youngin's in college? Because they talk about how "physics is such a part of their brain, and it's just how they operate." or they're overly excited with scholastic jargon like "inductive reasoning" etc.

Most of us have degrees, we know what that shit means, you don't have to impress us. Stop talking like a douche. It's like when middle schoolers learn how to cuss without their mom hearing, they over use it and get annoying. Your 1st post would have been like 1 paragraph, and easy to read if you cut the BS

Yes and no. The typical progressive bumpstop + soft spring setup is as I described. (factory cars are like this) They start to get stiffer after you start compressing the suspension. So over most of the travel the springs are soft, and they stiffen up before the suspension bottoms, which it does while cornering.

The Xida srings are set up where the soft springs only begin to unblock when the suspension droops some distance. What it does is give you a stiff setup, but if the car wants to catch air, you have a soft sprung setup past a certain point with add'l droop travel. In cornering on smooth pavement the stiff springs don't unblock.

Without the soft springs the stiff spring will flop, or the droop travel limited (by the shocks) and the tires will catch air more easily. Without the add'l droop travel the resulting landing will be much more harsh because the shocks don't have the distance over which to travel and provide compression damping.

So the "dualness" of the Xidas serve a different purpose than bumpstops progressiveness. The latter gives you a smooth ride when driving sedately and prevents the outside of the car compressing heavily in hard cornering. It doesn't prevent the inside of the car from lifting lots. Long progresive bumpstops also prevents the feeling of abrupt bottoming on large bumps (as opposed to short stiff bumpstops). If you look at stock miatas in autox the inside lifts a lot more (big wheel gap) than the outside compresses (due to the bumpstops).

The typical "progressive" aftermarket springs are a bit like the Xidas in that at rest the soft part is blocked. Of course the Xidas have bumpstops, but they are not nominally engaged while cornering, they are there for large bumps.

That's true if the Miata has more RC vertical travel per CG vertical travel. Is this the case?

ACTUALLY, sir, the reason my first post was so long was mainly due to a pretty high level of sleep deprivation (4hours sleep, 48 hours awake) and since communication is by far my least natural and most contrived skill the resultant post was an unorganized compilation of the thoughts running through my head. AND the reason I'm offended enough to make this post is that I heavily denounce the forces of scholastic bullshit and academic arrogance, but I promise you if "i'm talking like a douche" it's because I lack a complete understanding of the topic I'm asking a question about and am trying my best to provide clarity in my reasoning so that my question is more accurately understood. some of it is just how I think though and I fail to filter it out, but I try not to "impress" anymore than needed to deter responses lacking enough detail to be useful.

Sorry if this part is offensive, but based on your dialect and dislike of "the youngins" would you perhaps be religious? As a secular anti-federalist who believes in the good of atheism, living in Georgia my whole life has allowed to me to form a pretty good stereotype, but if I could sharpen it enough to be able to judge people over the internet by text only that would be great. I admire your sharpened stereotype for "the youngins" and can only hope to refine my own even further.

Thanks for posting a perfect example of more of what I'm talking about.
Your post could have said something to the effect of: "How was my first post douchey? I'm just trying to learn. Are you a crabby old bastard?"

^see how concise and easy to read that was? I said the same thing, in very little space, without all the self-righteous multi-syllable words.

FYI: I'm a stark atheist who majored in philosophy, listens to hip-hop and has a sneaker collection. Nice try. I'm also only 24, so actually I am under the demographic I threw you in, and was simply trying to explain to you why older folks all hate US.
Older people love to talk smack on folks in their teens and early 20's, and it's because of some dumb shit we do. I figured out at least one and was putting you ahead of the curve.

This.

Yes.

I came back for more JACKING FORCE. I am disappointed.

haha, nice. #OFWGKTA (...lol) The use of "douche" should've given it away. I just have trouble with verbal communication sometimes as I'm very "math/sci minded" most of my understanding of "normal/social" communication is only semi-natural since a lot of it was learned through observation and having a red rx-8 + liver strength in high school ...0_0

You definitely have a point and I have a habit of being excessively lengthy in how I talk, but I just feel like short/concise communication can lack accuracy and unintentional implications. I also feel, out of forming a lot of my own ideas and sometimes arrogance, I need detail to describe things which aren't implied. In "normal/social" conversation, where the purpose isn't purely exchange of technical knowledge/ideas, or even if its, I can not only utilize tone, humility, and a respectful attitude to communicate that my lengthy conversation is for accuracy and not self-righteous boasting but I can also make it more concise because due to the more frequent exchanges of words I can tell through both the response to my question and reading body language whether or not I've lost any accuracy in shortening my question or am sounding douchey by adding superfluous detail. It usually works really well though because at the core of it I'm asking sincerely. If I haven't sleep or am tired or even just in an insane mood... all that just goes out the window and I'm "blah blah blah blah blah" or just know better than to try to talk when I'm tired, a ranty forum post is just too tempting sometimes though :D


I wouldn't come back to this thread unless you see a response from someone like JasonC, who's knowledge and understanding I respect more with every post. Which reminds me...

@Jason, if the spring is just flat-out too hard and you hit a bump it's going to upset the chassis beyond the point of where it could be practically "calmed down", so what really determines how hard of a spring you can use while dealing with bumps will be in the high speed damping of the shock right? If expecting to encounter bumps on hard springs, less high speed compression damping (the harder spring should help to slow the momentum of the sprung mass) and a bit more damping on HS rebound would be effective? negatives to that?

My "still forming" and moderate understanding of suspension geometry was all I had to contribute. If you wait for the next thread I'll actually have some "quantified evaluation" :3 on the lateral load transfer resulting from the playing with CoG and roll center height.

Anyways.

Nick. Do you have a turbo?

Wow. I know you're smoking the reefer and probably running on adderal, but WTF are you really on? Dope? Lucy? Whitney?

Chill the fuck out.

brb, slamming my car. with chrome wheels.

I'm sick and tired of this "higher spring rates, use less compression damping" myth. Do a search for my posts on this topic on miata.net. Bot compression and rebound damping damp the spring-mass SYSTEM.

The *bounce frequency* aka spring stiffness should be as soft as possible that keeps you off or in a reasonable part of the bumpstop while cornering while having enough remaining bump travel to absorb bumps. The conflicting requirement is that you want the car as low as possible to lower the CG as much as possible.

Softer springs is better BUT the conflicting requirement is you don't want a shit ton of body roll because that adversely affects the tire's camber while cornering, and said body roll also compresses the outside suspension reducing remaining available bump travel.

Softer springs is better because the tires will have more grip on bumps. This is the only reason softer springs is better.

With the conflicting requirements there is a compromise that depends on the road surface primarily. The smoother the surface the lower and stiffer you can run. For bumpy backroads you will need a softer taller setup.

For lower grip conditions (e.g. rain) you will have less body roll generated so you can make the setup softer but also lower. Additionally in the wet tires lose more grip when they pass their peak grip point (in their slip angle curve). This means when you get in a slide it takes longer to regain grip. So you don't want to lose grip in the first place, so the setup needs to be softer than dry conditions.

That's the general guidelines. As to the optimal setup, you would have to look at who's fast. 949 seems to have found a fast track setup. Fatcat has nice setups for autox and backroads. It is 949 that has found that very low and very stiff works well for the track.

Not yet, I was so close to just buying the EFR6258 so I could stare it, but I spent most of the "turbo setup" money on more tooling and a TIG welder instead. Attachment 241024

That phone picture is huge..., but if I can get just a little better than that, I should be able to make money with it.

WOW I wish I could weld like that.

Dann

Meanwhile in the Ohlins TTX manual:

So I guess it depends, even if it doesn't turn up in simple simulated spring mass damper systems.

Show me a damper that adjusts both compression and rebound with a single knob, that reduces the compression damping while increasing the rebound.

rofl how many beads is on that plate? I like the one in the top right... looks like turd. :D

The energy transfer occurring between the stored kinetic energy of the sprung mass and potential energy of the spring reminded me of, in a frictionless world, the mechanical equivalent of a lossless resonant LC circuit, where an E&M instead of K&P conversion takes place between a capacitor and an inductor (like mass&spring) and a resistor damps the oscillatory transfer.

The damping "level" is described in terms of Q, for quality. High Q, less loss, less damping; Low Q, more loss, more damping.
"A system with low quality factor (Q < ½) is said to be overdamped. Such a system doesn't oscillate at all, but when displaced from its equilibrium steady-state output it returns to it by exponential decay, approaching the steady state value asymptotically. It has an impulse response that is the sum of two decaying exponential functions with different rates of decay."
"A system with high quality factor (Q > ½) is said to be underdamped. Underdamped systems combine oscillation at a specific frequency with a decay of the amplitude of the signal. Underdamped systems with a low quality factor (a little above Q = ½) may oscillate only once or a few times before dying out."
"A system with an intermediate quality factor (Q = ½) is said to be critically damped. Like an overdamped system, the output does not oscillate, and does not overshoot its steady-state output (i.e., it approaches a steady-state asymptote). Like an underdamped response, the output of such a system responds quickly to a unit step input. Critical damping results in the fastest response (approach to the final value) possible without overshoot. Real system specifications usually allow some overshoot for a faster initial response or require a slower initial response to provide a safety margin against overshoot."
Q=1/2 would be a balanced system, having a linear response.

A significant difference between a spring&mass system in comparison to an LC circuit exists and should be noted since it appears to be relevant to our suspensions. Although "0.5kx^2 and 0.5mv^2" are equivalent in that they're both simple integrals of force in respect to distance, the concerning difference is between x^2, where x=displacement, and v^2, where v=velocity. In the event a large "unexpected" force is applied to the wheel, such as a bump, it works out to where there will be a larger imbalance of stored energy between the sprung mass and the spring. The larger the force, the faster the sprung mass will travel, and the kinetic energy will build as the square of the velocity. I'm nearly positive this is why "high speed" damping adjustment exists, because you want to transfer that energy imbalance into the spring more quickly in order to maintain tire compliance you will need less damping to maintain a linear response. I think that a slightly underdamped shock compression going over a bump, responding quickly and exponentially in position/time (aka overshoot) will upset the chassis the least in the event of a bump (noting that our spring&mass system has a frequency too low to oscillate or repeat itself at all in the short timeframe of this event) and a slightly "overdamped" shock rebound will then respond with an inversely-exponential position/time, which would make the resultant wheel position/time graph very closely mimic a bump.

Well, if you reduce compression with a single knob, the amount of rebound is increased relatively :D Seriously though, the amount of damping needed varies with the "unpredictable force" dependent velocity of the sprung mass and being slightly underdamped improves response time and being a little further from "correct damping" appears to more effectively deal with a "bump". It almost makes you want to feed a linear pot value divided by sampling interval into a PID loop controlling a solenoid field around a damper full of ferrofluid 0_0

Your point being that öhlins have just identified themselves as idiots?

"An indicator of too much suspension pressure is controllable sliding at all speeds and all phases throughout the turns (flat sliding). "

Balls..... my stock bilsteins on my 94 R are blown, I "flat slide" pretty easily.... :(. They are at 175k miles, though.

Put it this way. The quote from the manual you posted is technobabble to me. (Kind of like "Fedspeak")
What year BTW is that manual, and does the current one still have that paragraph?

Big companies can have one department designing hot shit stuff, then a newbie in a pissant department writing documentation... I've seen it many times.

Think about this. If you have a linear spring, and if the car doesn't hit the bumpstops, the mass/spring/damper system is linear. Why should the bump and rebound be asymmetric? Then, think. What is the asymmetry in the system, or desired asymmetric behavior, that justifies asymmetric damper curves?

I would think a bump or any force causing the assembly to act like something other than simply an oscillating spring&mass would be the "asymmetry" due to the exponential energy imbalance (wutta term...) of the sprung mass receiving an external force. This, http://949racing.com/xida-coilover-miata.aspx also implies a non-linear system, right?

Wrong, and quite the opposite. As Army officers my sons were taught at West Point to communicate in a short/concise manner specifically to enhance accuracy and to eliminate unintentional implications. Fortunately you're not writing orders, or you'd kill battalions.

As another example, I'm reminded of the fellow who apologized to a valued friend for not taking the time to write a shorter letter. He was too rushed to cull out the unnecessary bullshit and so his friend was forced to wade through it to get his meaning, hence, the apology. Cull out the unnecessary bullshit.

And btw, that sentence I quoted of yours is an example of why you should write less, but better. Read it and you'll see you've said "short/concise communication can lack unintentional implications". I'm pretty sure you didn't really mean that, but with all the other nonsense I can't be sure.

I'm sure you've got lots to say without quadrupling it. We're not idiots, usually, and can read between the lines; just leave some room between the lines and we'll do the rest. And edit a bit for God's sake! Oy!

Being an old bastard I have to google this shit to see what you young'ens are talking about. I left out the semi-colon and got, "Tenderloin District". Knowing Hustler's ways I thought this was his way of telling the OP he was going to take him down to the Tenderloin and, you know, teach him the ropes. With the ";" I get a completely different result.:facepalm:

This is the most pedantic bullshit I've possibly EVER read. When you get your head out of your ass you'll realize this too. I'm normally a mild mannered man, but I really want to bitch slap you right now, Nick. :vash:

Don't take this wrong, Nick, I'm saying this for your own good. Someday you'll thank me.:fawk:

I like turtles.

Drop spindles///thread

don't blame me, its the counterproductive public education system and their nonsensical ideology that increased workload and lengthy essays somehow make students more useful to society... :D

No. I tried to warn you. You just won't listen.