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Racer
 
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Quote:
Originally Posted by Bill Verburg View Post
Yes, raising the spindle changes the angle of the control arm, when the outer end is raised(or the inner end lowered) the IC is lowered which also lowers the roll center. The CG also is lowered. Due to the leverage inherent in the geometry the IC drop exceeds the CG drop, thus lengthening the roll moment arm. Most would agree that this is not an improvement. But of course you are entitled to you own opinion.
Wow, Bill. Are you off your game?

First, when the spindles are raised, the outer end of the A-arm is lowered, not raised. The IC is raised as is the roll center. All good things for a lowered 911.

Second, raising the spindles only lowers the CG *if* the front of the car is lowered more after the spindles have been raised. Most of the time you are after a certain front ride height and raise the spindles to restore proper geometry and gain shock travel.

Raising the spindles does several things. Look here:

changing front roll center height worth it with spindle change?
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Old 05-31-2017, 09:34 AM
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If you want to really mess with your brain, start using Google to figure out why engineers wouldn't put roll center at CG height (no roll?) or even above (would a car lean into a turn?)
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Old 05-31-2017, 09:37 AM
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Originally Posted by Driven97 View Post
If you want to really mess with your brain, start using Google to figure out why engineers wouldn't put roll center at CG height (no roll?) or even above (would a car lean into a turn?)
It's called "jacking forces". Some roll is good. It allows the suspension to help the tires when turning the car.
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Old 05-31-2017, 09:47 AM
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Well I know, I was directing that at the OP. Knowledge is power.
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Old 05-31-2017, 09:50 AM
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Quote:
Originally Posted by winders View Post
Wow, Bill. Are you off your game?

First, when the spindles are raised, the outer end of the A-arm is lowered, not raised. The IC is raised as is the roll center. All good things for a lowered 911.

Second, raising the spindles only lowers the CG *if* the front of the car is lowered more after the spindles have been raised. Most of the time you are after a certain front ride height and raise the spindles to restore proper geometry and gain shock travel.

Raising the spindles does several things. Look here:

changing front roll center height worth it with spindle change?
My bad, the raised spindle neither changes the cg nor changes the control arm angle in and of itself For the CG to change the car ride height must changed. The point of raising the spindle is bump steer control when the ride height is lowered. When the car is lowered it also lowers the cg, and at the same time lowers the inner end of the arm, this lowers the IC and RC

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Old 05-31-2017, 01:37 PM
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Quote:
Originally Posted by Bill Verburg View Post
My bad, the raised spindle neither changes the cg nor changes the control arm angle in and of itself For the CG to change the car ride height must changed. The point of raising the spindle is bump steer control when the ride height is lowered. When the car is lowered it also lowers the cg, and at the same time lowers the inner end of the arm, this lowers the IC and RC

Bill,

You are still missing it. The main point of raising the spindles is to raise the roll center. How? When you raise the spindles, what has to happen to the control arm outer end? It gets closer to ground. So, whatever the ride height is set to, the roll center is higher than if the spindles were not raised.

Raising the spindles makes the bump steer situation worse which is why the bump steer kits extend the attachment point for the tie rods down to better match the curve the A-arms travel.
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Old 05-31-2017, 01:53 PM
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Originally Posted by winders View Post
Chill? I was emphasizing that roll center does not change because you have torsion bars or coilovers or because the mass changes. Where did I suggest CG didn't change when mass is moved around?

If I were yelling, my text would be in all caps....
i also said the roll center dosent change so whats the problem with my first post again???

i was trying elude up to what I think the op was trying to convey with the CG. no roll center change but a move up in the CG couple with the existing roll center location does change the dynamics. minimal yes but a change never the less !!!

do you get my drift!!!

i hope so !!!

:-) !!!
Old 05-31-2017, 03:19 PM
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Quote:
Originally Posted by Bill Verburg View Post
My bad, the raised spindle neither changes the cg nor changes the control arm angle in and of itself For the CG to change the car ride height must changed. The point of raising the spindle is bump steer control when the ride height is lowered. When the car is lowered it also lowers the cg, and at the same time lowers the inner end of the arm, this lowers the IC and RC

bill

when lower the car significantly the roll center goes subterranean, not really what u want. in effect reduces the resistance to roll.

also you may lose camber gain with a drastically dropped car on stock geometry not design to run that low... not that there is a lot with the standard 911 McPherson geo anyhow.

i believe these are the two main fixes for drop spindles .

in a nutshell, drop spindles enable the a drastically lowered car to get its RC back closer to the stock location . typically this means the lower suspension arm is near horizontal along the ground plane keeping the IC up above the ground (glancing at a factory drawings shows angle to move the IC just a tad up).

little correction on your comment above, yes all things being equal it will either change the angle of the suspension arm if you shoot for the same stock ride height or change the CG if the lower arm is in the same location. with raise spindles you cant have both were it once was and thats the whole point of it right?

bumpsteer does not not always get better with raised spindles by itself (us old alfa guys call it drop spindles cuz it drops the car). it does reduce the lateral displacement of the wheel/hub/steering arm which may help when a car is lowered without DS. but its not nearly enough.

too minimize bumpsteer the steering tie rods should be near parallel with the lower arm if you draw a line between the inner pick up and the outer ball joint. when you add raised spindles this relationship changes by splaying outer end of the steering tie rod out further than the inners in front view. Hence the value of a bumpsteer kit bring it back down.

now who will be a first to offer a drop spindle with the associate relocated shorten steering arms and possibly a steering rack displacement feature? this would eliminate the need for a bumpsteer kit and have faster steering response . guys can slam their cars with smaller 15inch wheels with the RC in the right place and have a quicker steering ratio in one full swoop. :-)

respectfully pf
Old 05-31-2017, 04:28 PM
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Quote:
Originally Posted by panzerfaust View Post
bill

when lower the car significantly the roll center goes subterranean, not really what u want. in effect reduces the resistance to roll.

also you may lose camber gain with a drastically dropped car on stock geometry not design to run that low... not that there is a lot with the standard 911 McPherson geo anyhow.

i believe these are the two main fixes for drop spindles .

in a nutshell, drop spindles enable the a drastically lowered car to get its RC back closer to the stock location . typically this means the lower suspension arm is near horizontal along the ground plane keeping the IC up above the ground (glancing at a factory drawings shows angle to move the IC just a tad up).

little correction on your comment above, yes all things being equal it will either change the angle of the suspension arm if you shoot for the same stock ride height or change the CG if the lower arm is in the same location. with raise spindles you cant have both were it once was and thats the whole point of it right?

bumpsteer does not not always get better with raised spindles by itself (us old alfa guys call it drop spindles cuz it drops the car). it does reduce the lateral displacement of the wheel/hub/steering arm which may help when a car is lowered without DS. but its not nearly enough.

too minimize bumpsteer the steering tie rods should be near parallel with the lower arm if you draw a line between the inner pick up and the outer ball joint. when you add raised spindles this relationship changes by splaying outer end of the steering tie rod out further than the inners in front view. Hence the value of a bumpsteer kit bring it back down.

now who will be a first to offer a drop spindle with the associate relocated shorten steering arms and possibly a steering rack displacement feature? this would eliminate the need for a bumpsteer kit and have faster steering response . guys can slam their cars with smaller 15inch wheels with the RC in the right place and have a quicker steering ratio in one full swoop. :-)

respectfully pf
The spindles are not dropped. They are raised on the strut body. Yes, I see you call that out...but it confuses the situation when you use incorrect terminology.
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Old 05-31-2017, 04:46 PM
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As stated, raising the spindles (or changing any of the suspension pickup points for that matter) will affect roll center [once you alter the ride height accordingly]. There are a number of variables to consider when making a change such as spindle height, so to get a good answer you'd need to plot your suspension, taking into account things like ride height and tire/wheel diameter. I spent some good time playing with a suspension design and analysis program designing a new front suspension for my racecar, so have had my fill of this.

To the OP, I wonder if you were also mixing unsprung weight into your question without actually stating it? Coil springs are pretty light, so have minimal impact on car weight due to the small percentage of total that they comprise. Unsprung weight is much less, so there would be some increase when adding coils. Torsion bars are heavy, but they are also at the pivot point of the A arm so contribute minimally to unsprung weight (and in fact I believe this is why Porsche liked torsion bars back in the day). With all of that said, most racers choose coilovers because they're easier to adjust and easier to swap out for other springs when setting up a car.

Last edited by stownsen914; 05-31-2017 at 07:30 PM..
Old 05-31-2017, 07:25 PM
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Quote:
Originally Posted by jamesjedi View Post
I think I am understanding this a little more - the distance between the C of G and the RC is called the roll moment. With 73 RSR or any other car that has its spindles raised, the distance of the roll moment is actually increased. This happens even though the C of G has been lowered, as has the RC. It sounds like a confusing compromise.

This guy helped me in understanding a LITTLE bit;

https://www.youtube.com/watch?v=yU2c03KkF6k

I did some reading before playing with the suspension design program to understand things like roll center, scrub, anti-dive/squat, etc. There is a lot to consider, and optimizing one often causes compromises in others. It's also not easy to get the guys who really know what's best for critical things like roll center to spill the beans! But from what I gather, the sweet spot for roll center is usually between ground and several inches above ground, and it's preferable to have the rear roll center above the front roll center to make for predictable handling. For center of gravity, naturally lower is better, but usually it's above the roll center.

As a point of reference, 914s have a high rear roll center. Depending on how the car is set up, I think it winds us being like 5-6 inches above ground. When you spring a 914 stiffly, many do away with the rear sway bar (including yours truly), which is consistent with the lower roll couple that comes with a high roll center. Think of it as the car (CG) having less leverage on the RC, so less sway bar is needed to resist roll.
Old 05-31-2017, 07:56 PM
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Quote:
Originally Posted by stownsen914 View Post
I did some reading before playing with the suspension design program to understand things like roll center, scrub, anti-dive/squat, etc. There is a lot to consider, and optimizing one often causes compromises in others. It's also not easy to get the guys who really know what's best for critical things like roll center to spill the beans! But from what I gather, the sweet spot for roll center is usually between ground and several inches above ground, and it's preferable to have the rear roll center above the front roll center to make for predictable handling. For center of gravity, naturally lower is better, but usually it's above the roll center.

As a point of reference, 914s have a high rear roll center. Depending on how the car is set up, I think it winds us being like 5-6 inches above ground. When you spring a 914 stiffly, many do away with the rear sway bar (including yours truly), which is consistent with the lower roll couple that comes with a high roll center. Think of it as the car (CG) having less leverage on the RC, so less sway bar is needed to resist roll.
914's have normal trailing arms, no? Not even semi-trailing arms like a 911 as I understand.

Trailing arm suspensions or any other suspensions in which the wheel does not move laterally as it moves up and down will have a static roll center at ground level. The FVSA length is infinite and perpendicular to the plane of wheel motion.

When you have unequal contribution of cornering force between the inside and outside tires, the effective roll center is closer to the line of action for the stronger (outside) tire so the roll center will be a little above ground when turning (due to body roll).
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Old 05-31-2017, 10:00 PM
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Originally Posted by Flieger View Post
914's have normal trailing arms, no? Not even semi-trailing arms like a 911 as I understand.

Trailing arm suspensions or any other suspensions in which the wheel does not move laterally as it moves up and down will have a static roll center at ground level. The FVSA length is infinite and perpendicular to the plane of wheel motion.

When you have unequal contribution of cornering force between the inside and outside tires, the effective roll center is closer to the line of action for the stronger (outside) tire so the roll center will be a little above ground when turning (due to body roll).

It is a semi-trailing arm actually. Somewhat less "semi" than a 911, but if you plot the pickup points it becomes obvious.
Old 06-01-2017, 04:00 AM
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Originally Posted by winders View Post
Bill,

You are still missing it. The main point of raising the spindles is to raise the roll center. How? When you raise the spindles, what has to happen to the control arm outer end? It gets closer to ground. So, whatever the ride height is set to, the roll center is higher than if the spindles were not raised.

Raising the spindles makes the bump steer situation worse which is why the bump steer kits extend the attachment point for the tie rods down to better match the curve the A-arms travel.
ok, I see what you are saying
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Old 06-01-2017, 06:54 AM
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Originally Posted by winders View Post
The spindles are not dropped. They are raised on the strut body. Yes, I see you call that out...but it confuses the situation when you use incorrect terminology.
"The spindles are not dropped" like duh.... they call them drop spindles cuz they drop the body or the ride height of the car.

much like "staggered tires" means something entirely different to the oval track racers who has used the term decades before the ricers adapted it and often used here. not so much incorrect just different.

Last edited by panzerfaust; 06-01-2017 at 07:46 AM..
Old 06-01-2017, 07:39 AM
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Originally Posted by stownsen914 View Post
As stated, raising the spindles (or changing any of the suspension pickup points for that matter) will affect roll center [once you alter the ride height accordingly]. There are a number of variables to consider when making a change such as spindle height, so to get a good answer you'd need to plot your suspension, taking into account things like ride height and tire/wheel diameter. I spent some good time playing with a suspension design and analysis program designing a new front suspension for my racecar, so have had my fill of this.

To the OP, I wonder if you were also mixing unsprung weight into your question without actually stating it? Coil springs are pretty light, so have minimal impact on car weight due to the small percentage of total that they comprise. Unsprung weight is much less, so there would be some increase when adding coils. Torsion bars are heavy, but they are also at the pivot point of the A arm so contribute minimally to unsprung weight (and in fact I believe this is why Porsche liked torsion bars back in the day). With all of that said, most racers choose coilovers because they're easier to adjust and easier to swap out for other springs when setting up a car.
coils may have another advantage for less twisting or binding of the front suspension itself.
Old 06-01-2017, 07:48 AM
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Originally Posted by panzerfaust View Post
coils may have another advantage for less twisting or binding of the front suspension itself.
Coils buckle and put a side load on the strut/damper. For a strut there are already side loads but for the rear it adds friction/binding to the suspension by loading the damper seals.
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Old 06-01-2017, 09:50 PM
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Originally Posted by stownsen914 View Post
It is a semi-trailing arm actually. Somewhat less "semi" than a 911, but if you plot the pickup points it becomes obvious.
The roll center will still be very low then.
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Old 06-01-2017, 09:51 PM
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Originally Posted by Flieger View Post
The roll center will still be very low then.

It doesn't work out that way on 914 at least. Roll center location depends entirely on pickup point geometry. In the case of a 914 the roll center is relatively high. Plotting it tells the story.
Old 06-02-2017, 06:09 AM
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Originally Posted by Flieger View Post
Coils buckle and put a side load on the strut/damper. For a strut there are already side loads but for the rear it adds friction/binding to the suspension by loading the damper seals.
perhaps...

stiction is the phrase commonly used for the side load friction/bind. like the flexing of the chassis under dynamic condition. pretty difficult for us hobbyist to measure.
Old 06-02-2017, 12:33 PM
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