SLAM IT BRO Large Roll Couples = bad4pussies High Roll Centers = INSIDE LIFT MORE BAD
06-14-2011, 07:48 PM
#22
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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.
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06-15-2011, 11:28 PM
#24
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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.
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.
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...
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06-15-2011, 11:58 PM
#25
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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...
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...
Last edited by JasonC SBB; 06-16-2011 at 01:26 PM.
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06-16-2011, 12:24 AM
#26
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"?
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"?
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06-16-2011, 02:39 AM
#28
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The problem with progressive springs 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...
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...
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06-16-2011, 12:45 PM
#30
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 **** 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
Most of us have degrees, we know what that **** 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
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06-16-2011, 01:21 PM
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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.
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.
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06-16-2011, 03:23 PM
#33
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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 **** 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
Most of us have degrees, we know what that **** 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
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.
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06-16-2011, 03:52 PM
#34
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.
blah blah blah
As a secular anti-federalist who believes in the good of atheism...
blah more bullshit
blah blah blah
As a secular anti-federalist who believes in the good of atheism...
blah more bullshit
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 **** we do. I figured out at least one and was putting you ahead of the curve.
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06-16-2011, 04:09 PM
#37
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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.
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.
I came back for more JACKING FORCE. I am disappointed.
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06-16-2011, 07:53 PM
#38
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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 **** we do. I figured out at least one and was putting you ahead of the curve.
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 **** we do. I figured out at least one and was putting you ahead of the curve.
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
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.
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