Adjustable Roll Center Adjusters.
12-18-2011, 11:36 AM
#1
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Adjustable Roll Center Adjusters.
Ok so my understanding of Roll Center Adjusters
is predicated upon the premise that the vehicle
in question (Civic EG) is lowered very low.
But if we were to take a look at each manufacturers
RCA's and compare their lengths
1. Would they all be the same length?
2. And is it the length of the ball joint that
Sets the stage on which one must lower their vehicle very low?
3. Would shortening the balljoint to achieve original suspension arm geometry in a lowered vehicle achieve the desired affects which a RCA claims to achieve w/out going very low?
is predicated upon the premise that the vehicle
in question (Civic EG) is lowered very low.
But if we were to take a look at each manufacturers
RCA's and compare their lengths
1. Would they all be the same length?
2. And is it the length of the ball joint that
Sets the stage on which one must lower their vehicle very low?
3. Would shortening the balljoint to achieve original suspension arm geometry in a lowered vehicle achieve the desired affects which a RCA claims to achieve w/out going very low?
12-21-2011, 12:37 PM
#3
Re: Adjustable Roll Center Adjusters.
1. No, not necessarily. You can expect them all to be around 3/4" though.
2. I guess so. See below.
3. I don't follow you here.
You don't need to lower the car excessively to fit these, in fact fitting them will lower the car by roughly the amount they extend the balljoint by anyway. People usually advise against fitting these on a mildly lowered car because they don't fully understand the effects they have, but I have heard of people fitting these on cars lowered only 1" with no ill effects to note.
2. I guess so. See below.
3. I don't follow you here.
You don't need to lower the car excessively to fit these, in fact fitting them will lower the car by roughly the amount they extend the balljoint by anyway. People usually advise against fitting these on a mildly lowered car because they don't fully understand the effects they have, but I have heard of people fitting these on cars lowered only 1" with no ill effects to note.
12-22-2011, 04:44 AM
#4
Re: Adjustable Roll Center Adjusters.
Raising your roll center will reduce traction at that end of the vehicle. This is pretty common knowledge in suspension tuning. Not really something desirable for the front of a FWD (more under-steer). There is evidence of this because EVERY single person that installs them says "The steering is so much lighter now, EVERYONE must try these!!!".
The real issue these companies are trying to sell you is Bump-steer. Lowering a car will increase bump steer (how much, we don't know). Spoon is the only company that actually calls these bump-steer correction. The funny part is that not one single company will provide any actual measurements or information specific to any given chassis or setup to inform the customer and back up their claims. Instead they show a generic drawing of some imaginary lowered chassis with the suspension arms pointing all crazy. This is not YOUR car.
Bottom line. Of course they "can" correct bump-steer. But only for a VERY specific ride height. A part such as this would best be used in conjunction with other suspension mods (maybe softer front springs) while testing/tuning on a track where 10ths of a second are important.
PS: If you don't have ride-height adjustable suspension, these won't change the angle of your arms whatsoever. They will just lower the car more (and add more camber) as Komodo mentioned. Kinda the exact opposite of what they advertise.
The real issue these companies are trying to sell you is Bump-steer. Lowering a car will increase bump steer (how much, we don't know). Spoon is the only company that actually calls these bump-steer correction. The funny part is that not one single company will provide any actual measurements or information specific to any given chassis or setup to inform the customer and back up their claims. Instead they show a generic drawing of some imaginary lowered chassis with the suspension arms pointing all crazy. This is not YOUR car.
Bottom line. Of course they "can" correct bump-steer. But only for a VERY specific ride height. A part such as this would best be used in conjunction with other suspension mods (maybe softer front springs) while testing/tuning on a track where 10ths of a second are important.
PS: If you don't have ride-height adjustable suspension, these won't change the angle of your arms whatsoever. They will just lower the car more (and add more camber) as Komodo mentioned. Kinda the exact opposite of what they advertise.
12-23-2011, 04:30 AM
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Re: Adjustable Roll Center Adjusters.
Raising your roll center will reduce traction at that end of the vehicle. This is pretty common knowledge in suspension tuning. Not really something desirable for the front of a FWD (more under-steer). There is evidence of this because EVERY single person that installs them says "The steering is so much lighter now, EVERYONE must try these!!!".
The real issue these companies are trying to sell you is Bump-steer. Lowering a car will increase bump steer (how much, we don't know). Spoon is the only company that actually calls these bump-steer correction. The funny part is that not one single company will provide any actual measurements or information specific to any given chassis or setup to inform the customer and back up their claims. Instead they show a generic drawing of some imaginary lowered chassis with the suspension arms pointing all crazy. This is not YOUR car.
Bottom line. Of course they "can" correct bump-steer. But only for a VERY specific ride height. A part such as this would best be used in conjunction with other suspension mods (maybe softer front springs) while testing/tuning on a track where 10ths of a second are important.
PS: If you don't have ride-height adjustable suspension, these won't change the angle of your arms whatsoever. They will just lower the car more (and add more camber) as Komodo mentioned. Kinda the exact opposite of what they advertise.
The real issue these companies are trying to sell you is Bump-steer. Lowering a car will increase bump steer (how much, we don't know). Spoon is the only company that actually calls these bump-steer correction. The funny part is that not one single company will provide any actual measurements or information specific to any given chassis or setup to inform the customer and back up their claims. Instead they show a generic drawing of some imaginary lowered chassis with the suspension arms pointing all crazy. This is not YOUR car.
Bottom line. Of course they "can" correct bump-steer. But only for a VERY specific ride height. A part such as this would best be used in conjunction with other suspension mods (maybe softer front springs) while testing/tuning on a track where 10ths of a second are important.
PS: If you don't have ride-height adjustable suspension, these won't change the angle of your arms whatsoever. They will just lower the car more (and add more camber) as Komodo mentioned. Kinda the exact opposite of what they advertise.
12-23-2011, 05:50 AM
#6
Re: Adjustable Roll Center Adjusters.
I'm sorry, but I couldn't say. If your racing (those sound like "race-car" springs), you would have to test them on your specific setup at any given time to see if they will help you shave some lap time or help inspire more confidence on the track.
If this is a street car, then save your money.
If this is a street car, then save your money.
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12-23-2011, 02:35 PM
#8
Re: Adjustable Roll Center Adjusters.
True......but again there's no real measuring and testing. Just opinions & driving impressions (which could be biased due to a lightened wallet). Yes, I know I'm a pessimistic skeptic. :D
Still may be worth a shot though if you have no suspension mods left to make, and your trying to eek out that last bit. The more I read about them, the more tempting they become (as usual). May even allow me to move my front GC top-hats to the back.
Still may be worth a shot though if you have no suspension mods left to make, and your trying to eek out that last bit. The more I read about them, the more tempting they become (as usual). May even allow me to move my front GC top-hats to the back.
12-24-2011, 01:05 PM
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Re: Adjustable Roll Center Adjusters.
Just thought about it and perhaps all I have to do is measure the angle of the suspension arms at stock height and simply calculate the difference the RCA's will make and than calculate how much to lower the car in order to return the suspension arms to their original angles.
Are my math skills up to the challenge?
Are my math skills up to the challenge?
12-25-2011, 02:36 PM
#10
Re: Adjustable Roll Center Adjusters.
The problem is you have to measure based on the pivot point of the bushings and the ball joints. Not the arm itself. The pivot point of the lower ball joint is actually inside the knuckle, so the angle of the arm is misleading. Kinda like this picture:
Please let us all know if you get it.
Please let us all know if you get it.
01-03-2012, 01:14 PM
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Re: Adjustable Roll Center Adjusters.
94 eg has the right answer. Unless the taper is offset which lowers the pivot point or node. These rcas do nothing. The arms can end up in anyshape or form and it will not make any difference until the nodes are moved. But these do make free up a little space. Nice 94eg!
01-03-2012, 01:19 PM
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Re: Adjustable Roll Center Adjusters.
To truely correct bumpsteer the location of the rack or the angle between the rack and the upright/spindle must be changed. The rcas if they do work will change the rate of camber. There is a relation bt them. But the bumpteer is a mere function of camber
01-05-2012, 01:23 AM
#13
Re: Adjustable Roll Center Adjusters.
The problem is you have to measure based on the pivot point of the bushings and the ball joints. Not the arm itself. The pivot point of the lower ball joint is actually inside the knuckle, so the angle of the arm is misleading. Kinda like this picture:
Please let us all know if you get it.
Please let us all know if you get it.
01-05-2012, 10:09 AM
#14
Re: Adjustable Roll Center Adjusters.
What I'm trying to show with the drawing is how the visual angle (black lines) of the arm is misleading. You cannot look at at your arms and say, yes they are at angle X, or even measure them with a protractor. It's the imaginary red dashed-line between the two pivot points that is important. There is no good way to measure this because the outer pivot point is buried deep inside the ball joint and a physical angle does not exist.
No worries.
It's definitely not a case of moving the entire suspension & steering system up. In fact it's all much less complicated than that. All unequal length double wishbone suspensions have bump-steer no matter what. It cannot be eliminated. You can only minimize it. While camber does have a small effect on bump-steer, it's incredibly minimal. For near-zero bump-steer, it is said that ideally all three control arms will point at one imaginary point in space called the "instant center" (see 1st pic below). In fact, the tie-rod location is not really important as long as it points at the instant center (see 2nd pic below).
When you lower the car, this intersection moves down and in towards the wheel. But the intersection for three arms does not move the same. The intersection of the UCA and tie-rod ends up being higher than the intersection of the UCA and LCA. This is called a bump-out condition (see 3rd pic below). By altering the angle of the LCA with "roll-center adjusters", the arm would ideally become pointed right at the new instant center where the UCA already intersects the tie rod. This will bring bump-steer back to "normal".
Now as you can imagine, it all depends on exactly how much your lowered, and exactly how much the RCA's alter LCA angle. Without any real data, your just shooting in the dark. You can bet these companies do know the exact changes per their design. But I bet they specifically designed the part for their own specific project-vehicle setup, and then recoup the costs by mass producing and selling as a universal part. Not a bad thing, but is it really something you need?
01-05-2012, 12:59 PM
#15
Re: Adjustable Roll Center Adjusters.
Yes, RC adjusters do move the pivot point. Sorry, but I just stole that pic. I didn't realize the text on the pic was from another subject matter about a different vehicle (ball joint is in the LCA on that car).
What I'm trying to show with the drawing is how the visual angle (black lines) of the arm is misleading. You cannot look at at your arms and say, yes they are at angle X, or even measure them with a protractor. It's the imaginary red dashed-line between the two pivot points that is important. There is no good way to measure this because the outer pivot point is buried deep inside the ball joint and a physical angle does not exist.
No worries.
What I'm trying to show with the drawing is how the visual angle (black lines) of the arm is misleading. You cannot look at at your arms and say, yes they are at angle X, or even measure them with a protractor. It's the imaginary red dashed-line between the two pivot points that is important. There is no good way to measure this because the outer pivot point is buried deep inside the ball joint and a physical angle does not exist.
No worries.
Top stuff, thanks for sharing. I note that in the third picture the inner tie rod pickup is higher on the chassis than the other two which obviously affects the intersection point. Is this an intentional exaggeration? Obviously if the point was in the same location as the other images then the change in intersection would not be so pronounced...
01-05-2012, 01:39 PM
#16
Re: Adjustable Roll Center Adjusters.
Yeah, it was just another stolen pic to help explain. This is kinda how your suspension looks when you lower, though this is WAY exaggerated. It just illustrates the difference.
I did do some autocad drawing that illustrate a real difference, but they came out pretty confusing, so I didn't make pics out of them.
If you look at the pic, you can see that your options to get all three pointing at one point are either of the following:
- lower the lower ball joint
- raise the outer tie-rod ball joint
As you can see, roll center adjusters lower the outer ball joint and thereby "could" accomplish this alignment.
The weird part is that, contrary to popular belief, you don't WANT to straighten your tie-rods when you lower. Hardrace makes a "super tie-rod" that allows you to mount under the knuckle. They say they will help bump-steer, but it's actually making it EVEN WORSE. This is a prime example of companies selling parts that people don't need simply because they will buy them. Even their sales description says these should be combined with RCA's which is just double-retarded. A fool and his money soon part ways.
http://www.jhpusa.com/store/pc/viewP...idproduct=8571
I did do some autocad drawing that illustrate a real difference, but they came out pretty confusing, so I didn't make pics out of them.
If you look at the pic, you can see that your options to get all three pointing at one point are either of the following:
- lower the lower ball joint
- raise the outer tie-rod ball joint
As you can see, roll center adjusters lower the outer ball joint and thereby "could" accomplish this alignment.
The weird part is that, contrary to popular belief, you don't WANT to straighten your tie-rods when you lower. Hardrace makes a "super tie-rod" that allows you to mount under the knuckle. They say they will help bump-steer, but it's actually making it EVEN WORSE. This is a prime example of companies selling parts that people don't need simply because they will buy them. Even their sales description says these should be combined with RCA's which is just double-retarded. A fool and his money soon part ways.
Originally Posted by JHPUSA
Used in conjunction with roll center adjusters (aka extended lower ball joints), you will have the ultimate steering input with minimal bump steer in your EG/EK/DC2 machine in a road racing environment! Not many companies offer race tie rods like these in this market!
Note: HR Super Tie Rod ends mount upside down to the knuckle assembly as opposed to right side up (like OEM). This helps correct tie rod geometry on lowered EG/EK/DC2 vehicles by keeping them horizontally straight and parallel to the front lower control arms rather than angled upwards when the weight of the car is on the ground.
Note: HR Super Tie Rod ends mount upside down to the knuckle assembly as opposed to right side up (like OEM). This helps correct tie rod geometry on lowered EG/EK/DC2 vehicles by keeping them horizontally straight and parallel to the front lower control arms rather than angled upwards when the weight of the car is on the ground.
01-05-2012, 02:09 PM
#17
Re: Adjustable Roll Center Adjusters.
Okay guys, I took the time to make a nice drawing that depicts exactly what we are talking about. This should really help with any confusion. Here I've drawn a "theoretical" suspension. The first step shows a near-zero bump-steer condition with all three arms pointing perfectly at the Instant Center (IC).
The second step shows as it's lowered a bit. You can see the IC has moved down and towards the wheel a bit, but the tie-rod is now slightly off.
The third step shows it lowered now twice as much. The IC has moved further in and much lower. And the tie-rod is now quite a bit off the mark.
Keep in mind this is not our cars. This just a quick illustration for example. Then I could do some real bump-steer calcs. I wish I knew the exact dimensions of the Civic/Teg geometry.
Bottom Line: Does this misalignment cause a significant amount of bump-steer to warrant spending hard-earned dollars to fix? Will your dollars even fix it? Who knows! If you just love working on suspension, and spending money on your car, these may be something to try. Just do the research, and be aware of the changes
Raised roll center = less grip & less bump-steer
The second step shows as it's lowered a bit. You can see the IC has moved down and towards the wheel a bit, but the tie-rod is now slightly off.
The third step shows it lowered now twice as much. The IC has moved further in and much lower. And the tie-rod is now quite a bit off the mark.
Keep in mind this is not our cars. This just a quick illustration for example. Then I could do some real bump-steer calcs. I wish I knew the exact dimensions of the Civic/Teg geometry.
Bottom Line: Does this misalignment cause a significant amount of bump-steer to warrant spending hard-earned dollars to fix? Will your dollars even fix it? Who knows! If you just love working on suspension, and spending money on your car, these may be something to try. Just do the research, and be aware of the changes
Raised roll center = less grip & less bump-steer
01-06-2012, 01:06 AM
#19
Re: Adjustable Roll Center Adjusters.
Lets take this as standard ride height. ICs are way outside of the image here, but the track rods insect at the IC.
Toe angle is -.003° (closest I can get to 0) at this ride height.
At 1/2" bump it's -.150°
At 1/2" rebound it's .191°
So a difference of .341° over 1" travel.
Now we drop 1", re-align to -.007° toe and do the sweep again
Track rod intersect is now well off the IC.
At 1/2" bump it's -.112°
At 1/2" rebound it's .124°
So a difference of .234° over 1" travel. Which appears to be LESS bump steer?!
Oh well, ploughing on...
Adding 3/4" RCAs and readjusting the ride height and alignment:
At 1/2" bump it's .479°
At 1/2" rebound it's -475°
So a difference of .954°
Now, I know the model isn't accurate, but these are some strange results going on your (and the RCA manfrs) theory, lowering improves bumpsteer and RCAs appear to have made it worse.
Regardless of the accuracy, it certainly questions the theory that the track rods need to point at the IC to minimise bumpsteer. I will need to read up in RCVD on this, however I am going on holiday this evening so won't be able to until a week Monday at the latest.
My guess would be that the angle of the track rod relative to the LCA is of more importance than its intersection with the IC (note the angle of the LCA and track rod in image 2, most parallel and least bump steer). It appears to be more to do with the arc it follows relative to the control arms, which would make the length a factor also. I had previously 'known' (through playing with this model) this to be the case but your posts made me question it and go back to check. Now hopefully you'll question my methods and we can get a better understanding of what is going on... Peer review is good.
01-06-2012, 01:21 AM
#20
Re: Adjustable Roll Center Adjusters.
Looking at those images, the angle relative to the LCA is definitely a major contributor:
Image 1 the track rod is at a negative angle (pointing downwards towards the LCA), we get toe in on bump, toe out on rebound and the moderate angle gives moderate bump steer.
Image 2 we get a fairly parallel but still slightly negative LCA:TR angle. Toe in again on bump, toe out in rebound but less of each.
Image 3 we have a large positive LCA:TR angle, toe out in bump, toe in on rebound and have a large amount of both.
Image 1 the track rod is at a negative angle (pointing downwards towards the LCA), we get toe in on bump, toe out on rebound and the moderate angle gives moderate bump steer.
Image 2 we get a fairly parallel but still slightly negative LCA:TR angle. Toe in again on bump, toe out in rebound but less of each.
Image 3 we have a large positive LCA:TR angle, toe out in bump, toe in on rebound and have a large amount of both.
01-06-2012, 05:02 AM
#21
Re: Adjustable Roll Center Adjusters.
Holly ****! Those images are really great! lol Thanks for posting that Komodo. This is the first time I've seen a real Civic suspension model. Is this an EK or EG/DC model?
Looking at the picture with both L & R suspension mocked up at the same time is a little confusing. It kinda appears the tie-rods are extending in the opposite direction to the control arms on the same side. If so, that's not quite a comparison to what I've drawn. Are you sure your talking about them pointing at the correct IC? I'm not criticizing, I just want to be sure.
Any chance we could get this same toe sweep at -2.5" with stock geometry (my street setup on an EG)? :D
Again, a huge thanks for posting this!
BTW: Anybody else getting the feeling that the Civic suspension was meant to be lowered?
Looking at the picture with both L & R suspension mocked up at the same time is a little confusing. It kinda appears the tie-rods are extending in the opposite direction to the control arms on the same side. If so, that's not quite a comparison to what I've drawn. Are you sure your talking about them pointing at the correct IC? I'm not criticizing, I just want to be sure.
Any chance we could get this same toe sweep at -2.5" with stock geometry (my street setup on an EG)? :D
Again, a huge thanks for posting this!
BTW: Anybody else getting the feeling that the Civic suspension was meant to be lowered?
01-06-2012, 05:14 AM
#22
Re: Adjustable Roll Center Adjusters.
Looking at the picture with both L & R suspension mocked up at the same time is a little confusing. It kinda appears the tie-rods are extending in the opposite direction to the control arms on the same side. If so, that's not quite a comparison to what I've drawn. Are you sure your talking about them pointing at the correct IC? I'm not criticizing, I just want to be sure.
Just for teh lolz:
Simulated corner exit with combined lift, roll and steer calculated from my dynamics spreadsheet...
Last edited by Kozy.; 01-06-2012 at 06:23 AM.
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01-06-2012, 05:22 AM
#23
Re: Adjustable Roll Center Adjusters.
Just swapped the projection lines from the tie rods to the correct side and yes, it would appear the least bump steer does infact happen when it intersects close to the IC. No need to run the model again though as I didn't need to change any geometry.
No, it's probably my rack location it was very hard to measure. Moving it as little as 0.1" vertically is enough to locate the intersect on the IC, and a switch either side of it determines the toe-in/out characteristics.
No, it's probably my rack location it was very hard to measure. Moving it as little as 0.1" vertically is enough to locate the intersect on the IC, and a switch either side of it determines the toe-in/out characteristics.
Last edited by Kozy.; 01-06-2012 at 05:42 AM.
01-06-2012, 06:04 AM
#24
Re: Adjustable Roll Center Adjusters.
Relocated the rack by .12" to point the tie rod at the IC.
Stock - Tie rod within .15" vertically of IC.
1/2" bump = .017°
1/4" bump = .003°
Standard ride height = .004°
1/4" rebound = -.001°
1/2" rebound = .013°
(I'm guessing here if I could get the IC spot on and the alignment perfectly striaght, this would sit at 0 and toe out equally in both directions)
Lowered 1" - Tie rod .75" below IC.
1/2" bump = .068°
1/4" bump = .033°
Standard ride height = .000°
1/4" rebound = -.028°
1/2" rebound = -.050°
Lowered 1" with 3/4" RCA - Tie rod 6.39" below IC
1/2" bump = .635°
1/4" bump = .318°
Standard ride height = -.005°
1/4" rebound = -.332°
1/2" rebound = -.662°
This would explain why it is not recommended to use RCAs when only moderately lowered.
Stock - Tie rod within .15" vertically of IC.
1/2" bump = .017°
1/4" bump = .003°
Standard ride height = .004°
1/4" rebound = -.001°
1/2" rebound = .013°
(I'm guessing here if I could get the IC spot on and the alignment perfectly striaght, this would sit at 0 and toe out equally in both directions)
Lowered 1" - Tie rod .75" below IC.
1/2" bump = .068°
1/4" bump = .033°
Standard ride height = .000°
1/4" rebound = -.028°
1/2" rebound = -.050°
Lowered 1" with 3/4" RCA - Tie rod 6.39" below IC
1/2" bump = .635°
1/4" bump = .318°
Standard ride height = -.005°
1/4" rebound = -.332°
1/2" rebound = -.662°
This would explain why it is not recommended to use RCAs when only moderately lowered.
Last edited by Kozy.; 01-06-2012 at 06:25 AM.
01-06-2012, 07:24 AM
#25
Re: Adjustable Roll Center Adjusters.
Wow. So it would seem my original drawings still hold true then?
I'm surprised the bump-steer is SO sensitive to rack location. Great work on your part to try all that. I guess it all just depends on EXACTLY what ride height Honda has designed the tie-rods to point at the IC.
Maybe you can also figure out what ride height the 3/4" RCAs would bring the 3 arms into alignment? I don't know how difficult this program is to work with. I'm guessing the car would have to be pretty low.
BTW: That last picture is really cool. It looks as though the inside lifts more than the outside dips in a turn. I'm kinda surprised. That's look due to the front is lifting under acceleration? On a side note, I read that if you severly limit droop, you can really alter cornering ability. The car will only dip on the outside and you will gain more camber and a lower ride height through the turn (lower CG). This can increase corner speed a bit. Also droop limiting on the front can help keep weight on the front tires too. All this was in relation to RC car tuning, and EVERYTHING is easily adjusted on those chassis.
I'm surprised the bump-steer is SO sensitive to rack location. Great work on your part to try all that. I guess it all just depends on EXACTLY what ride height Honda has designed the tie-rods to point at the IC.
Maybe you can also figure out what ride height the 3/4" RCAs would bring the 3 arms into alignment? I don't know how difficult this program is to work with. I'm guessing the car would have to be pretty low.
BTW: That last picture is really cool. It looks as though the inside lifts more than the outside dips in a turn. I'm kinda surprised. That's look due to the front is lifting under acceleration? On a side note, I read that if you severly limit droop, you can really alter cornering ability. The car will only dip on the outside and you will gain more camber and a lower ride height through the turn (lower CG). This can increase corner speed a bit. Also droop limiting on the front can help keep weight on the front tires too. All this was in relation to RC car tuning, and EVERYTHING is easily adjusted on those chassis.