Ride height: Positive Rake vs. Negative Rake
Dec 18, 2007, 05:38 PM
#76
I hear on that last part; and I agree on the sliding thing. I'm trying to get the car absolutely nuetral--only sliding the rear slightly when I decide to do it.
I don't mess with left foot braking all that much, but do heel-toe (or rev match). What's the coasting thing a big deal for? I coast all the time on the street!
I don't mess with left foot braking all that much, but do heel-toe (or rev match). What's the coasting thing a big deal for? I coast all the time on the street!
Dec 18, 2007, 05:45 PM
#77
I have a hard time truly trusting my brakes. After a long straight where speeds are triple digits I have a hard time going from WOT to last minute just in time braking. I tend to brake too early. The fellas I race with are darn near professionals and I drive them nuts with the "coasting". Unfortunately they have money to burn and I need to drive my car to work on Monday so we don't drive the same way.
Dec 18, 2007, 06:06 PM
#78
I think what I just typed, with too many words, says that RC correction kit is as effective with stiffer suspension as long as you're lowered and screwed the geometry and what you typed with less words said they are less effective when suspension is stiffened.
Dec 18, 2007, 06:25 PM
#79
I think what he meant was the that effects are less evident with a stronger spring rate, which is true; but like you and I said it's only masking the inherent problem.
My car's spring rates do a good job of keeping the roll to a minimum...even without the kit installed; but I'm doing it anyway because I know the problem exists and don't want my shocks compensating for something that can be corrected the "right way".
My car's spring rates do a good job of keeping the roll to a minimum...even without the kit installed; but I'm doing it anyway because I know the problem exists and don't want my shocks compensating for something that can be corrected the "right way".
Dec 18, 2007, 06:40 PM
#80
If you compare this to a softer spring rate, then the higher spring rate setup has effectively reduced the amount of elastic weight transfer by keeping keeping the RC closer to the sprung mass COG during a cornering situation. When there is less elastic weight transfer, there is less roll and so it might seem that the RC correction device has become less effective, but that is not the case - it has served the same purpose to the same degree, with the effect of the higher spring rate masking the benefits of the RC correction device.
edit: wow, treed by about 15 minutes...
Dec 18, 2007, 07:33 PM
#81
I think I know what you are talking about and I'd agree. Higher spring rates not only reduce RC migration during cornering, but a higher spring rate is simply more effective at resisting the lateral forces that are reacted through the springs, shocks and swaybars (elastic weight transfer).
If you compare this to a softer spring rate, then the higher spring rate setup has effectively reduced the amount of elastic weight transfer by keeping keeping the RC closer to the sprung mass COG during a cornering situation. When there is less elastic weight transfer, there is less roll and so it might seem that the RC correction device has become less effective, but that is not the case - it has served the same purpose to the same degree, with the effect of the higher spring rate masking the benefits of the RC correction device.
edit: wow, treed by about 15 minutes...
If you compare this to a softer spring rate, then the higher spring rate setup has effectively reduced the amount of elastic weight transfer by keeping keeping the RC closer to the sprung mass COG during a cornering situation. When there is less elastic weight transfer, there is less roll and so it might seem that the RC correction device has become less effective, but that is not the case - it has served the same purpose to the same degree, with the effect of the higher spring rate masking the benefits of the RC correction device.
edit: wow, treed by about 15 minutes...
A little off topic but the new coilovers are looking really good. My only concern is with the unknown spring rates, I'm ready to purchase but I wanna be sure I'm getting valving capable of supporting 12k/14k at least and that the rate is not reversed like some of the JDM ones. (You can pm me if getting them valved for my own custom rate is a possibility)
Sorry for jacking the thread.
Dec 19, 2007, 05:22 PM
#82
Somebody that understands the whole picture
A little off topic but the new coilovers are looking really good. My only concern is with the unknown spring rates, I'm ready to purchase but I wanna be sure I'm getting valving capable of supporting 12k/14k at least and that the rate is not reversed like some of the JDM ones. (You can pm me if getting them valved for my own custom rate is a possibility)
Sorry for jacking the thread.
A little off topic but the new coilovers are looking really good. My only concern is with the unknown spring rates, I'm ready to purchase but I wanna be sure I'm getting valving capable of supporting 12k/14k at least and that the rate is not reversed like some of the JDM ones. (You can pm me if getting them valved for my own custom rate is a possibility)
Sorry for jacking the thread.
You got pm!
Thanks Al.
Dec 21, 2007, 06:40 AM
#84
Evolving Member
Join Date: Nov 2006
Location: JHB
Posts: 116
Likes: 0
Received 0 Likes
on
0 Posts
Interesting thread.
Jeff makes a good point here missed by most, and as I also own a full corner weighting system by Intercomp for my tuning shop we put this to the test, and a harder ride only masks the deeper problem of how a car behaves on various tracks - Autocross/open high speed track or Gymkhana. (coilovers only - dont do spring setups!)
One thing you learn from prepping race cars where changes are constant and the effects noted, it that all the changes that make perfect sense on a static level car become worthless in a dynamic racing environment. In other words, corner weighting and suspension geometry is always track specific (and as important as tyre choice, track width, spring rate or CG).
Building a perfect static solution will leave your car neutral....and although this may work on track with no embankment, no hills or slopes, and a perfect level surface, everywhere else it will be found wanting, even on the road.
For most customers I have the battle is always deciding what’s more important…function or form. Most choose form, as it looks good!
Adelin
Dec 21, 2007, 09:52 AM
#85
Interesting thread.
Jeff makes a good point here missed by most, and as I also own a full corner weighting system by Intercomp for my tuning shop we put this to the test, and a harder ride only masks the deeper problem of how a car behaves on various tracks - Autocross/open high speed track or Gymkhana. (coilovers only - dont do spring setups!)
One thing you learn from prepping race cars where changes are constant and the effects noted, it that all the changes that make perfect sense on a static level car become worthless in a dynamic racing environment. In other words, corner weighting and suspension geometry is always track specific (and as important as tyre choice, track width, spring rate or CG).
Building a perfect static solution will leave your car neutral....and although this may work on track with no embankment, no hills or slopes, and a perfect level surface, everywhere else it will be found wanting, even on the road.
For most customers I have the battle is always deciding what’s more important…function or form. Most choose form, as it looks good!
Adelin
Jeff makes a good point here missed by most, and as I also own a full corner weighting system by Intercomp for my tuning shop we put this to the test, and a harder ride only masks the deeper problem of how a car behaves on various tracks - Autocross/open high speed track or Gymkhana. (coilovers only - dont do spring setups!)
One thing you learn from prepping race cars where changes are constant and the effects noted, it that all the changes that make perfect sense on a static level car become worthless in a dynamic racing environment. In other words, corner weighting and suspension geometry is always track specific (and as important as tyre choice, track width, spring rate or CG).
Building a perfect static solution will leave your car neutral....and although this may work on track with no embankment, no hills or slopes, and a perfect level surface, everywhere else it will be found wanting, even on the road.
For most customers I have the battle is always deciding what’s more important…function or form. Most choose form, as it looks good!
Adelin
Having your roll center above ground statically is what you want because the RC will migrate dynamically on a favorable horizontal plane above ground with a beneficial roll couple.
Having your static roll center subterranean (underground) due to the change in geometry as a result of lowering and your dynamic migration will be on that same horizontal plane but still subterranean while the stiffer suspension would only dictate how fast and how far the RC migrates.
This link is a paper written by Steve Sulatycki at ZZYZX motorsports [They have one of the baddest coilovers for the evo (koni based) ]
It should help you understand what I'm talking about a little better
http://zzyzxmotorsports.com/library/...h-20070918.pdf
Last edited by madmax199; Dec 21, 2007 at 10:15 AM.
Jan 3, 2008, 06:29 PM
#86
Again, stiffer springs and antiroll bars only slowdown and and resist roll center migration on an horizontal plane(from centerline of the car to right or left).
Having your roll center above ground statically is what you want because the RC will migrate dynamically on a favorable horizontal plane above ground with a beneficial roll couple.
Having your static roll center subterranean (underground) due to the change in geometry as a result of lowering and your dynamic migration will be on that same horizontal plane but still subterranean while the stiffer suspension would only dictate how fast and how far the RC migrates.
This link is a paper written by Steve Sulatycki at ZZYZX motorsports [They have one of the baddest coilovers for the evo (koni based) ]
It should help you understand what I'm talking about a little better
http://zzyzxmotorsports.com/library/...h-20070918.pdf
Having your roll center above ground statically is what you want because the RC will migrate dynamically on a favorable horizontal plane above ground with a beneficial roll couple.
Having your static roll center subterranean (underground) due to the change in geometry as a result of lowering and your dynamic migration will be on that same horizontal plane but still subterranean while the stiffer suspension would only dictate how fast and how far the RC migrates.
This link is a paper written by Steve Sulatycki at ZZYZX motorsports [They have one of the baddest coilovers for the evo (koni based) ]
It should help you understand what I'm talking about a little better
http://zzyzxmotorsports.com/library/...h-20070918.pdf
why doesn't this paper include the cg or roll couple sizes?
shorter would appear to be better... less migration to me would be the guess as to what is better... but i'm confused a bit at the mixed results or rather i'm most confused by how the blue x seems to move in the same direction every time (at least the other lines make it look that way) yet the off center track number shows positive for one and negative for the other.
i'd specifically like to know... if the roll center is the consequence/summation of many other component forces acting through interconnected/interrelated geometries, what does that say about an rc going toward the inside of the turn and one getting flung to the outside?
Last edited by trinydex; Jan 3, 2008 at 06:32 PM.
Jan 3, 2008, 06:52 PM
#87
the paper isn't elaborating enough. is there something else to read or can you explain the benefits of a subterranean roll center?
why doesn't this paper include the cg or roll couple sizes?
shorter would appear to be better... less migration to me would be the guess as to what is better... but i'm confused a bit at the mixed results or rather i'm most confused by how the blue x seems to move in the same direction every time (at least the other lines make it look that way) yet the off center track number shows positive for one and negative for the other.
i'd specifically like to know... if the roll center is the consequence/summation of many other component forces acting through interconnected/interrelated geometries, what does that say about an rc going toward the inside of the turn and one getting flung to the outside?
why doesn't this paper include the cg or roll couple sizes?
shorter would appear to be better... less migration to me would be the guess as to what is better... but i'm confused a bit at the mixed results or rather i'm most confused by how the blue x seems to move in the same direction every time (at least the other lines make it look that way) yet the off center track number shows positive for one and negative for the other.
i'd specifically like to know... if the roll center is the consequence/summation of many other component forces acting through interconnected/interrelated geometries, what does that say about an rc going toward the inside of the turn and one getting flung to the outside?
The roll center is not a result of any forces, it is a geometric concept, a result of the angles of various control arms (I think you know that?). Instant centers tend to shift towards the inside of a turn during roll, and so it follows that the RC will also shift towards the inside. I'm not sure in what situation the RC would move towards the outside, unless its a hard, severely off-camber turn that would cause the UCA on the inside corner to end up at less of an angle than the outside UCA.
Jan 3, 2008, 07:29 PM
#88
sprung mass CG is illustrated in the first diagram. For purposes of calculating roll center and RC migration, we can assume the CG is static. I agree, mitigating roll center migration is one of the primary goals of suspension tuning.
The roll center is not a result of any forces, it is a geometric concept, a result of the angles of various control arms (I think you know that?). Instant centers tend to shift towards the inside of a turn during roll, and so it follows that the RC will also shift towards the inside. I'm not sure in what situation the RC would move towards the outside, unless its a hard, severely off-camber turn that would cause the UCA on the inside corner to end up at less of an angle than the outside UCA.
The roll center is not a result of any forces, it is a geometric concept, a result of the angles of various control arms (I think you know that?). Instant centers tend to shift towards the inside of a turn during roll, and so it follows that the RC will also shift towards the inside. I'm not sure in what situation the RC would move towards the outside, unless its a hard, severely off-camber turn that would cause the UCA on the inside corner to end up at less of an angle than the outside UCA.
i guess the reason i say that rc is the resultant point from a lot of different component forces is because i read this: http://zzyzxmotorsports.com/library/...nd-reality.pdf
maybe that's not what that paper is sayin either.... there are many more grammatical errors in this second pdf which leads me to believe it was either hastily done or done by someone who's an engineer that doesn't care about english... neither which i fancy much but i'll read what i can get.
Last edited by trinydex; Jan 3, 2008 at 07:31 PM.
Jan 3, 2008, 07:47 PM
#89
Oh damn, my mistake. For some reason, when I saw the link that Madmax posted I thought it was the article that YOU just posted. So I did not in fact read the first one 
Jan 3, 2008, 07:54 PM
#90
i don't know about you guys but i'm reading this myths on roll center for the third time and it's sooooo annoying. maybe someone can like explain or teach me because some of the stuff said just doesn't seem valid.
Myth #3: The distance from the kinematic roll center to the CG is the moment arm.
If you believe in the kinematic roll center it is easy to consider the distance to the CG as a moment arm. A long distance from KRC to CG produces lots of chassis roll. The problem is that this line is not perpendicular to the lateral force. The FAPs, defined as being under the CG, yield a moment arm perpendicular to the lateral force. The distance from FAP to CG is a valid moment arm.
while the FAP to CG moment arm is more succinct it's not to say that the RC to CG moment arm is void. it's still an arm, just because it's 40 feet long in the lateral direction and 4" tall in the vertical does not invalidate it as an arm. c'mon just break down the components the damn thing is GENERATED from component forces anyway.
http://fsae.com/eve/forums/a/tpc/f/1.../m/36310598241
this just adds to my confusion
Myth #3: The distance from the kinematic roll center to the CG is the moment arm.
If you believe in the kinematic roll center it is easy to consider the distance to the CG as a moment arm. A long distance from KRC to CG produces lots of chassis roll. The problem is that this line is not perpendicular to the lateral force. The FAPs, defined as being under the CG, yield a moment arm perpendicular to the lateral force. The distance from FAP to CG is a valid moment arm.
while the FAP to CG moment arm is more succinct it's not to say that the RC to CG moment arm is void. it's still an arm, just because it's 40 feet long in the lateral direction and 4" tall in the vertical does not invalidate it as an arm. c'mon just break down the components the damn thing is GENERATED from component forces anyway.
http://fsae.com/eve/forums/a/tpc/f/1.../m/36310598241
this just adds to my confusion