SLAM IT BRO Large Roll Couples = bad4pussies High Roll Centers = INSIDE LIFT MORE BAD - Miata Turbo Forum - Boost cars, acquire cats.

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Old 06-14-2011, 03:03 AM   #1
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Default 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 **** 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 ([email protected] 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 Boy I tell you gotdamn? what the baby-snatchin tornado that I cannut wait to start jiggin and TIG'n YEEEEHAAWWWW.
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Old 06-14-2011, 03:06 AM   #2
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wat.
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Old 06-14-2011, 03:07 AM   #3
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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.
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Old 06-14-2011, 03:07 AM   #4
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wat. wat.
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Old 06-14-2011, 03:51 AM   #5
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What the **** are you asking!?
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Old 06-14-2011, 03:57 AM   #6
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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...
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Old 06-14-2011, 04:02 AM   #7
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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
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Old 06-14-2011, 04:06 AM   #8
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Quote:
Originally Posted by JasonC SBB View Post
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...
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 **** was waayy bumpier than most backroads even.
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Old 06-14-2011, 04:24 AM   #9
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Quote:
Originally Posted by curly View Post
What the **** are you asking!?
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".

Last edited by NickC; 06-14-2011 at 04:35 AM.
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Old 06-14-2011, 05:16 AM   #10
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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
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Old 06-14-2011, 05:36 AM   #11
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More camber = better handling

/thread
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Old 06-14-2011, 05:39 AM   #12
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Was that a response to what I said or just your response to the whole thread?
Sorry, couldnt work it out.

Dann
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Old 06-14-2011, 07:05 AM   #13
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Get some sleep.
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Old 06-14-2011, 08:24 AM   #14
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Quote:
Originally Posted by rleete View Post
Get some sleep.
+99

Come back, slow down, speak in layman's terms, and give us some diagrams/graphs.
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Old 06-14-2011, 10:55 AM   #15
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The only thing I noticed in that first post was JACKING FORCE
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Old 06-14-2011, 11:51 AM   #16
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Why not work on the spindle side?
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Old 06-14-2011, 01:11 PM   #17
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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.
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Old 06-14-2011, 01:15 PM   #18
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tl;dr
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Old 06-14-2011, 02:02 PM   #19
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I think he's saying.... we all need AST's, 15x10s, and 275 ho-hos on our cars...... :-D
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Old 06-14-2011, 05:18 PM   #20
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Quote:
Originally Posted by nitrodann View Post
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
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
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