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Old 04-01-2014, 10:46 PM   #1
ManiacalZX3
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Post Need a Sway Bar Education!

Ok here goes. I know that adding a larger rear sway bar, or anti-roll bar, helps induce more over steer. But why? To me the how and why are just as important as the end result. The way I see it, the bars help reduce body roll by connecting the body to the suspension. Also, if a huge bar is used it makes the suspension act more like a solid axle in that what happens to one wheel affects the others.

So when a car tri-pods, the huge rear bar is forcing the opposite tire to stay up with the tire on the opposite side that is being compressed. Four tires have more traction than three tires any day of the week. So why does using a large rear bar that makes one tire come off the ground make the car go faster? I guess that could be reducing the rear grip is the same result as increasing front end traction?


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Old 04-03-2014, 08:19 AM   #2
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Old 04-03-2014, 09:46 AM   #3
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Quote:
Originally Posted by ManiacalZX3 View Post
So when a car tri-pods, the huge rear bar is forcing the opposite tire to stay up with the tire on the opposite side that is being compressed. Four tires have more traction than three tires any day of the week. So why does using a large rear bar that makes one tire come off the ground make the car go faster? I guess that could be reducing the rear grip is the same result as increasing front end traction?
It depends on the car and how it is set up.
An aggressive sway bar on a FWD car will make the rear end of the car rotate around corners, giving you more grip in the front which is how you go faster as the front wheels are doing the most work.
A RWD car with an aggressive rear sway bar will over-steer as well, but the reason it's slower is because you've essentially placed all the grip on the front wheels and they're not doing anything.
An AWD car with an aggressive rear sway bar will be slower than an AWD car with a more balanced suspension. Since all four tires are doing the work, you want to be planted at all times.

It's all relative though. You can't just put a huge rear sway bar and expect results. You have to tune the whole chassis to work the way you want to drive the car.
For instance, my stock SES suspension was relatively soft but the rear sway bar was stiffer than normal. It rotated very well, but it was too mushy everywhere else to be of any use. When I upgraded to the Ford Racing suspension, the mushy handling is gone, but now I need a stiffer sway bar to get the same kind of rotation.
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Old 04-03-2014, 10:49 PM   #4
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Quote:
Originally Posted by mac.mogul View Post
It depends on the car and how it is set up.
An aggressive sway bar on a FWD car will make the rear end of the car rotate around corners, giving you more grip in the front which is how you go faster as the front wheels are doing the most work.
A RWD car with an aggressive rear sway bar will over-steer as well, but the reason it's slower is because you've essentially placed all the grip on the front wheels and they're not doing anything.
An AWD car with an aggressive rear sway bar will be slower than an AWD car with a more balanced suspension. Since all four tires are doing the work, you want to be planted at all times.

It's all relative though. You can't just put a huge rear sway bar and expect results. You have to tune the whole chassis to work the way you want to drive the car.
For instance, my stock SES suspension was relatively soft but the rear sway bar was stiffer than normal. It rotated very well, but it was too mushy everywhere else to be of any use. When I upgraded to the Ford Racing suspension, the mushy handling is gone, but now I need a stiffer sway bar to get the same kind of rotation.
Though this is technically correct, there are many more factors involved.
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Old 04-04-2014, 06:23 AM   #5
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Quote:
Originally Posted by PowerFocer View Post
Though this is technically correct, there are many more factors involved.
What a great and informative post.




It is not the diameter of the bar that does the steering. It is how the bar reacts on the Camber and Toe.
As the suspension compresses so does negative Camber and negative Toe (Toe In). This means the tire wants to travel away from the direction of the corner. The more compression, the greater the Camber and Toe. And just to opposite on the extension side of the car, positive Camber and Toe Out.
The stiffer the bar, the less the change in Camber and Toe. Just the same as reducing suspension movement.


IMO, you want to get a good amount of seat time in with the car so you know your limit with it. If you are faster with how Camber and Toe interact in stock form, stick with it. If not, adjust to suit your driving style. There is no fastest setup or best setup. It's all the limit and ability of the driver.

A stiffer RSB may have faster turn in, but I really doubt it will post consistently faster lap times vs a proper alignment/suspension.
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Old 04-04-2014, 09:55 AM   #6
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Dennis does a great job of explaining suspension dynamics and how they apply to autocross.

http://farnorthracing.com/autocross_secrets.html
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Old 04-04-2014, 11:05 AM   #7
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Quote:
Originally Posted by pkolator View Post
Dennis does a great job of explaining suspension dynamics and how they apply to autocross.

http://farnorthracing.com/autocross_secrets.html
Bookmark this. Its pretty much the Autocross bible.
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Old 04-04-2014, 11:24 AM   #8
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That's a lot of deep, technical info. Good info, but not for the faint of heart.
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Old 04-04-2014, 03:36 PM   #9
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Problem I always have is, it's not specif to the Focus.
All suspension systems do not operate the same. Upper & lower A-Arm types do not function the same as McPherson type, 4-Link does not work like Control Blade.
I am feebly trying to fix that --> http://www.focusfanatics.com/forum/showthread.php?t=394154
& any technical help with that is appreciated
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Old 04-04-2014, 05:50 PM   #10
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Fort the OP at least, before we have fun with changing geometries & special cases like autocross....

Imagine an evenly balanced car when it's cornering, same slip front & rear - doesn't oversteer or understeer. Anti-roll bars added would be the same size front & rear to maintain this balance while helping the car corner flatter.

Now take one that's heavier in the front, front tends to slide out more (understeer) so speed is limited by that - once the front starts slipping you can't go faster & stay on the road. Adding a rear anti-roll bar (or larger in rear than front) puts more force on the outside rear tire so it starts slipping sooner. Front to rear balance is gained and you can round the corner without one end sliding more than the other.

Tail heavy? Might want more bar in the front so it doesn't stick TOO well as the tail comes around.

This leaves out a TON of details that can change the equation, driving wheels aren't even mentioned for starters. It DOES give an idea how anti-roll bars can be used to fine tune handling through use of different sizes front to rear.

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