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Damper settings/suspension geometry

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zzyzx said:
Here's what I consider to be a helpful example of how different parameters affect geometry for a strut based suspension:

http://zzyzxmotorsports.com/library/strut-tech-20070918.pdf

I'll simply add that irrespective of your target camber of -2.0, you should set your top camber plate to full negative (inboard). That will likely yield something > -2.0 in your case, so the bolts are not necessary. In fact, I'd advise against them unless you have an explicit need.

If you have any questions about the link I posted, let me know. Though at this point I take the concepts in there for granted, I realize that they are still in the "black art" realm for many. :D


Steve, Thanks for a great read and link. This help me understand more of the problems I am having and why.
 
1,022
99
Exp. Type
HPDE
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10-20 Years
Texas
zzyzx said:
Here's what I consider to be a helpful example of how different parameters affect geometry for a strut based suspension:

http://zzyzxmotorsports.com/library/strut-tech-20070918.pdf

I'll simply add that irrespective of your target camber of -2.0, you should set your top camber plate to full negative (inboard). That will likely yield something > -2.0 in your case, so the bolts are not necessary. In fact, I'd advise against them unless you have an explicit need.

If you have any questions about the link I posted, let me know. Though at this point I take the concepts in there for granted, I realize that they are still in the "black art" realm for many. :D

I read the article...So am I to understand that installing the extended steeda ball joints this would help to re-raise the roll center and improve the handling? I have the camber plates and plan on setting them at -2.0 and I will also install the bump steer kit. The car is being lowered by Eibach Sportlines. You can see the list of my mods in the first post. Thanks
 

Sesshomurai

Flyboygsxr said:
I read the article...So am I to understand that installing the extended steeda ball joints this would help to re-raise the roll center and improve the handling? I have the camber plates and plan on setting them at -2.0 and I will also install the bump steer kit. The car is being lowered by Eibach Sportlines. You can see the list of my mods in the first post. Thanks

I have all those parts now. Steeda cambers -2.0. Sportlines and steeda bumpsteer and ball joints. Will review after some track time.
 

zzyzx

Steve
299
0
Flyboygsxr said:
I read the article...So am I to understand that installing the extended steeda ball joints this would help to re-raise the roll center and improve the handling?

That's correct - it'll raise the roll center height.

Flyboygsxr said:
I have the camber plates and plan on setting them at -2.0 and I will also install the bump steer kit.

Just keep in mind that setting camber via camber plates is difficult to do on an alignment rack - the guy doing it won't want to unless you're at a race shop. This is why I generally recommend setting them prior to an alignment.

That said, never set the plates to different positions L/R to obtain "equal" camber L/R. As you can see from the diagrams, when you alter the position you're changing the front suspension geometry. If the plates are not in the same position L/R, your roll center will not be centered; it'll be skewed off to one side. This will lead to a difference is how the car handles when turning left & right.

Most cars have an OEM eccentric bolt on the upper hole of the strut to make fine adjustments to camber, and that's the preferred route if you set the camber plates to equal positions and end up with different L/R camber readings.

Unfortunately, Ford chose not to do this from the factory, so we're stuck buying a set of bolts, and having the "oval" the hole on our own.

I chose to go this route because I wanted to take an incremental approach to suspension setup, so all I've done so far are the camber bolts and tires... with dramatic results. I didn't realize until I got it on an alignment rack that I would get -2.7 deg. of camber with just the bolts. That's pretty much dead-on with where I wanted it to be, so I'm happy with the result.

The problem, however is that these bolts can "slip" and loosen over time. So, like I noted previously, I advise against them unless you really need them.

Flyboygsxr said:
The car is being lowered by Eibach Sportlines. You can see the list of my mods in the first post. Thanks

Ok, that being the case, it's my opinion you really don't need the extended ball joints. It's usually setups with coilovers that go too low and "invert" their front lower control arms as depicted in the diagrams, which is when the front geometry gets really screwed up.

The camber plates alone would be fine in your case, though one could always argue the extended ball joints could "help". In your case, certainly not nearly as much as a setup on coilovers that has been significantly lowered.

For a strut setup, all the theory and my personal experience boils down to a simple set of recommendations:

1. Never lower the car to the point where the inner pivot point is lower than the outer pivot point - what I call "inverted" front lower control arms. Level (e.g. parallel to the ground) is OK.

2. Always set your camber plates to equal positions L/R, regardless of your target camber. Fine adjustments to equal up camber L/F should be made at the eccentric bolt on the strut (if applicable). If you end up with 2-3 10ths of a degree difference L/R, better to leave it as-is rather than end up with a skewed roll center.

3. Target camber for "performance" applications should not be less than -2.5 or so. IMO, -2.0 is not enough camber to maximize grip and on the track will lead to more wear on the outside of the tire. Most (competitive) strut setups I've worked with over the years are at least -2.7, and are as often times around -3.0. Assuming you run zero toe, you should not expect unusual wear with even -2.5 or so. I run -2.7 with zero toe and my Boss is a daily and there's no uneven wear at this point. Same was true with my last Miata; but we know those little guys are easy on tires... :) Unlike some, I've seen no real benefit to "toe out" setups that is worth the additional tire wear.

On the theory side of things as depicted in the PDF I wrote, one of the goals is to minimize migration of the instant centers. If you have instant centers which have drastic migrations as a result of dynamic inputs, this translates roughly to observations we've all heard: "snap oversteer", "chassis doesn't settle down", "unpredictable handling".

Hope this helps. :)
 
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If a set of lowering springs like the Eibach sportlines have front/rear spring rates matched to each other relative to the amount of drop they give how will raising just the front roll center effect the handling balance? It would seem for the amount of money and effort to install an extended balljoint (a bumpsteer kit is mandatory) an adjustable front sway bar like the Hellwig or Whitline would be a good alternative.
 
zzyzx said:
That's correct - it'll raise the roll center height.
So you want to raise the roll center in the front and lower it in the rear?
 

zzyzx

Steve
299
0
cp85gt said:
If a set of lowering springs like the Eibach sportlines have front/rear spring rates matched to each other relative to the amount of drop they give how will raising just the front roll center effect the handling balance?

Let's break this down a bit and clarify. I'll assume what you're saying is that the ride height is lowered equal amounts F/R - let's say 1" and the rake (F ride height in relation to R ride height) does not change.

^ Let's say this is the only modification in question. So, the front of the car is now 1" lower, which means the front roll center would also be lower. How much depends on the geometry you start with, but it will certainly be lower, not higher. And, we know from the math that your roll center height will drop more quickly than your ride height. Thsi becomes obvious with "inverted" lower control arms and roll centers "below ground" (refer to the PDF).

The two things that's we discussed which change the relationship between your ride height and your roll center are:

1. Camber plate - relocation of upper strut pivot point.
2. Extended ball joints - relocation of lower control arm (LCA) outer pivot point.

How this affects your cars handling balance is not something easily quantified, other than to say that there are "rules of thumb" that you need to follow. Beyond that you'd need 1) empirical data and 2) a model specific to your setup.

Another concept which is important but not yet explicitly stated is the center of gravity (CoG). The F & R have a center of gravity upon which the lateral G forces act. For our purposes, we can think of ride height as the best approximation of CoG. The roll centers (instant centers...), are the geometric pivot points of the suspension upon which the CoG G-forces are applied to articulate the suspension.

The goal is the find the best compromise among the CoGs and instant centers which allow the suspension to work optimally producing the most predictable behavor and maximizing mechanical grip.

Simple enough, right? :eek:
 
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In the case of the Eibach sportline the rear drop is more than the front (1.0 vs 1.8) on the Boss, which is already a bit lower in the front than a standard GT. So without knowing how the front/rear geometry effects roll center when a car is lowered then there are 3 possibilities. 1) The front roll center is lowered more then the rear roll center. 2) The rear roll center is lowered more than the front. 3) The roll centers are lowered equally. It would seem that in only scenario (1) would the extended balljoint help to equalize roll centers, otherwise if you only raise the front roll center, then you could have a handling imbalance that would have to be adjusted out with sway bars, spring rates, tire width, etc.
The only empirical data I have with this is I was one of a few unfortunate souls to mix a Griggs front K-member with a Maximum Motorsports panhard bar on my Fox body. The front roll center was higher than the rear and the car pushed badly. I dialed out the understeer with sway bars. It would seem what Darren505 is doing by using the extended balljoint as a balance tuning idea would be where someone might get to eventually, not just an automatic upgrade when a car is lowered.
 

Sesshomurai

cp85gt said:
In the case of the Eibach sportline the rear drop is more than the front (1.0 vs 1.8) on the Boss, which is already a bit lower in the front than a standard GT. So without knowing how the front/rear geometry effects roll center when a car is lowered then there are 3 possibilities. 1) The front roll center is lowered more then the rear roll center. 2) The rear roll center is lowered more than the front. 3) The roll centers are lowered equally. It would seem that in only scenario (1) would the extended balljoint help to equalize roll centers, otherwise if you only raise the front roll center, then you could have a handling imbalance that would have to be adjusted out with sway bars, spring rates, tire width, etc.
The only empirical data I have with this is I was one of a few unfortunate souls to mix a Griggs front K-member with a Maximum Motorsports panhard bar on my Fox body. The front roll center was higher than the rear and the car pushed badly. I dialed out the understeer with sway bars. It would seem what Darren505 is doing by using the extended balljoint as a balance tuning idea would be where someone might get to eventually, not just an automatic upgrade when a car is lowered.

3) The roll centers are lowered equally.


From my measurements, the car is even front and rear (measure from the bottom of the apex of the inside wheel wheel edge) with the sportlines - and I have the ball joints on too.

I believe the stronger ball joints help in the front because the front takes more dive and abuse from braking than does the rear and it helps maintain the geometry when the car is articulated. But I still need to get it on track for a full empirical data on its affect in my car. I agree it probably is an optional element, but they are often coupled with bumpsteers which are a bit more necessary for fine tuning track performance on lowered cars.

Is there a good phone app that can measure roll center maybe? I will try to get precise measurements on my setup, but I also have eibach front/rear heavy duty sway bars and a 6 point roll bar too so my data will be a bit skewed.
 
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After looking at the front control arms they appear to be either parallel to the ground or slightly higher at the k-member attaching point with the stock springs. It is hard to tell exactly but it looks like the arm would become inverted with the 1" front drop. If you look at your set-up now with the extended balljoints, I bet they are back close to parallel. I don't think the Vorshlag car has extended balljoints. They just have 550 in/lb springs with a stiff adjustable sway bar to minimize body roll along with -4 degrees of camber. I'm looking forward to your track review.
 

Grant 302

basic and well known psychic
Awesome tech in this thread. Great posts, zzyzx.

Just curious, but the WinGEO models are 2-D and don't account for Caster effects, right? That would be awesome info! Still way better than any paper sketches I've made! :)

One of the reasons for leveling the front LCA is to minimize 'jacking' effects from that arm when turning. When not level, larger vertical force component will always be present, even at turn-in. This screws with the individual tire loading and maximum front grip available. ...At least that's *my* understanding!
 

Sesshomurai

zzyzx said:
...
2. Always set your camber plates to equal positions L/R, regardless of your target camber. Fine adjustments to equal up camber L/F should be made at the eccentric bolt on the strut (if applicable). If you end up with 2-3 10ths of a degree difference L/R, better to leave it as-is rather than end up with a skewed roll center.
...

Steve, you are a wealth of knowledge on this. Very interesting!

I don't have pics handy but after I told my shop to set my alignment to -2.0 camber, zero toe with my steeda camber plates, I saw in the engine bay that the driver strut top mount was "skew" (visible in the opening) compared to the passenger which was centered nicely in the strut top mount point opening. Is this what you mean by the above statement?

In terms of empirical handling the car turns a tad sharper to the left than the right (perhaps just my sensation), but since there's no passenger my weight could be affecting the balance turning left at higher speeds vs. right? (this was before some other recent mods like balljoints/bumpsteers). My car handles great in both directions but I'm now in the very fine tuning phase.

I asked the shop if this difference between the two strut top mount locations was an issue and they said "they would never be centered". Struck me as odd but my knowledge is still new here. Thanks for all the info.

Darren
 
zzyzx said:
For a strut setup, all the theory and my personal experience boils down to a simple set of recommendations:

1. Never lower the car to the point where the inner pivot point is lower than the outer pivot point - what I call "inverted" front lower control arms. Level (e.g. parallel to the ground) is OK.

2. Always set your camber plates to equal positions L/R, regardless of your target camber. Fine adjustments to equal up camber L/F should be made at the eccentric bolt on the strut (if applicable). If you end up with 2-3 10ths of a degree difference L/R, better to leave it as-is rather than end up with a skewed roll center.

3. Target camber for "performance" applications should not be less than -2.5 or so. IMO, -2.0 is not enough camber to maximize grip and on the track will lead to more wear on the outside of the tire. Most (competitive) strut setups I've worked with over the years are at least -2.7, and are as often times around -3.0. Assuming you run zero toe, you should not expect unusual wear with even -2.5 or so. I run -2.7 with zero toe and my Boss is a daily and there's no uneven wear at this point. Same was true with my last Miata; but we know those little guys are easy on tires... :) Unlike some, I've seen no real benefit to "toe out" setups that is worth the additional tire wear.

On the theory side of things as depicted in the PDF I wrote, one of the goals is to minimize migration of the instant centers. If you have instant centers which have drastic migrations as a result of dynamic inputs, this translates roughly to observations we've all heard: "snap oversteer", "chassis doesn't settle down", "unpredictable handling".

Hope this helps. :)

Really good info here. I really like point #2. You don't see that mention very often, and the illustration really helps to understand why it is important.
 

zzyzx

Steve
299
0
So, I decided to take a picture. This is from the front, looking at the passenger side LCA on my stock Boss:

boss302-stock-lca-angle.jpg


I'm surprised to say the least. It appears as if the LCA angle is nearly inverted from the factory. :eek:

Having seen this, I would indeed recommend the extended ball joints to correct the geometry if you're lowering the front end much at all. I guess I should have looked more closely before making any suggestions!
 

zzyzx

Steve
299
0
Grant 302 said:
Just curious, but the WinGEO models are 2-D and don't account for Caster effects, right? That would be awesome info! Still way better than any paper sketches I've made! :)

I'm not sure what you mean specifically, but it does model caster geometry in the side view. The diagrams in the PDF are for front view geometry. In the side view, caster is the delta between the upper mount point (e.g. the strut top/camber plate), and the lower ball joint (outboard) on the horizontal.

Many camber plates also provide for caster adjustment which is a good thing. The Ford OEM camber bolts also come with caster bolts, which I assume provide some eccentric adjustment so you can push the rear mount point of the LCA outboard, thus moving the outboard lower balljoint forward, providing additional positive caster.

On a strut based setup front caster is generally a good thing as it's the one way you can increase the dynamic camber gain with in a turn - dynamic camber gain as a result of steering angle. Unlike a nice SLA suspension (short long arm), struts have little in the way of dynamic camber gain, particularly under compression. Larger positive caster angle is one way to help with this deficiency. Caster also provides for a "self centering" load on the front wheels which may or may not be considered a good thing, depending on the application.
 

zzyzx

Steve
299
0
darreng505 said:
I asked the shop if this difference between the two strut top mount locations was an issue and they said "they would never be centered". Struck me as odd but my knowledge is still new here. Thanks for all the info.

All they're saying is that camber will never be equalized if you set both camber plates to the same positions L/R. If that is the reality you face, then the Ford camber bolts might be useful to equalize camber, after you've set the plates in the same positions L/R.
 

Grant 302

basic and well known psychic
zzyzx said:
I'm not sure what you mean specifically, but it does model caster geometry in the side view. The diagrams in the PDF are for front view geometry. In the side view, caster is the delta between the upper mount point (e.g. the strut top/camber plate), and the lower ball joint (outboard) on the horizontal.

Many camber plates also provide for caster adjustment which is a good thing. The Ford OEM camber bolts also come with caster bolts, which I assume provide some eccentric adjustment so you can push the rear mount point of the LCA outboard, thus moving the outboard lower balljoint forward, providing additional positive caster.

On a strut based setup front caster is generally a good thing as it's the one way you can increase the dynamic camber gain with in a turn - dynamic camber gain as a result of steering angle. Unlike a nice SLA suspension (short long arm), struts have little in the way of dynamic camber gain, particularly under compression. Larger positive caster angle is one way to help with this deficiency. Caster also provides for a "self centering" load on the front wheels which may or may not be considered a good thing, depending on the application.

I understand all that. :)

I was just misunderstanding the model in your pdf...I didn't notice any data with steering input that would get you to the 4 degrees of roll, and the related camber changes that would come with steering input. So I incorrectly assumed a 2D model. It was just simplified to explain roll centers and major effects from lowering.
 

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