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Author Topic:   Is one better than the other?
alias
Member
posted December 02, 2003 12:12 PM
I have seen some people raise the roll centers with longer upper ball joints, but I have seen others do it with longer lowers. Is one way better? Are there any advantages or disadvantages either way?


maxwell
Member
posted December 05, 2003 08:48 AM
Can anyone answer this ?


jammin
Administrator
posted December 05, 2003 09:06 AM
If you plot your roll center out, the longer ball joints will increase the angle of the upper A-arms...which will manipulate your roll center and usually make your instant center lower as well. The longer lower A-arms with the same spring will have a lighter spring rate at the tire than the shorter arms...keep this in mind because it will allow your car to roll more thinking you did the right thing when you just manipulated your spring pressures. But the roll center will also be affected upon the movement of the tires with the longer lowers some. But the lateral movement of the roll center is dependent more on the upper control arm angles than the lowers. It is pretty confusing until you take the time to plot it out, and then you can understand how everything affects it in the whole picture of things.

Hope this helps a little.

jammin


maxwell
Member
posted December 05, 2003 09:33 AM
quote:
Originally posted by jammin:
If you plot your roll center out, the longer ball joints will increase the angle of the upper A-arms...which will manipulate your roll center and usually make your instant center lower as well. The longer lower A-arms with the same spring will have a lighter spring rate at the tire than the shorter arms...keep this in mind because it will allow your car to roll more thinking you did the right thing when you just manipulated your spring pressures. But the roll center will also be affected upon the movement of the tires with the longer lowers some. But the lateral movement of the roll center is dependent more on the upper control arm angles than the lowers. It is pretty confusing until you take the time to plot it out, and then you can understand how everything affects it in the whole picture of things.

Hope this helps a little.

jammin



Thanks for the reply. My other question is what if I have to run stock uppers and lowers for a metric frame car what would you do to help your roll center. Longer ball joints on the upper or lower a frames

[This message has been edited by maxwell (edited December 05, 2003).]

jammin
Administrator
posted December 05, 2003 09:41 AM
The length really doesnt play as much role into the scenario as the angle comparison between the two, that is where you get your primary roll center manipulation...

The length will widen the front end's contact patch, but if you do it to both sides, you just made it even again....


jammin


alias
Member
posted December 05, 2003 09:48 AM
I re-read my post and saw that I did not
say longer lower "ball joints". Sorry about
that. I am in the same boat as Maxwell.
I have to run stock upper and lower a-frames
I have a pretty good understanding of roll
center and how to plot it out. I was just
wondering if it is better to raise your roll
center by using taller upper ball joints or
taller lower ball joints. We cannot use different a-frames on our cars. Metric frame
stuff only. The roll center on a stock metric frame is extremely low. It is pretty
easily raised with ball joints. You can manipulate the caster a little bit when you
put in different lowers. But I have never done anything with the uppers, so I was just
curious. Thanks for any info.


jammin
Administrator
posted December 05, 2003 10:15 AM
Personally, I would say use the longer uppers since it will not affect your ride height....

If you use longer lowers, your going to lower the car.

jammin


66jj
Member
posted December 05, 2003 02:01 PM

If you can run diff spindles I would run camaro big car etc.

If you do the work to plot it out on a program youll find theres quite a bit you can do. lower the upper mts, remove some anti dive, lower the center link by bending the pitman and idler.

But its all got to be precise. I have a couple hundred dollar computer program if someone with a metric wants to really spend the time measuring all the pts precisely I would work it in the computer for them.

You would need to measure everything, all mounting pts from centerline, on both sides, with it at ride ht, caster camber set etc.

Also form a line accross the front of the car and measure all the mounting pts from that line towards the rear, all measurements are from bj, tie rod pivot pt, etc.


If someone will really do it, Ill go into the program and can email blank sheets to you to print off and fill out with all the distances.

Ill be doing my nova/camaro pretty soon.


Jeff


zeroracing
Member
posted December 05, 2003 02:36 PM
some people use a tall ball joint on the right front and the stock length on the left front. This will offset the roll center......again, changing roll center.

This should not be MONKEY SEE, MONKEY DOOOO

You should know where you WANT to locate the roll center BEFORE deciding what is best for your chassis. the anlge of the upper will also have a great effect on the camber curve.


jammin
Administrator
posted December 05, 2003 09:50 PM
Very True Jeff....good point. May have to change upper A-arm lengths to compensate.

jammin

[This message has been edited by jammin (edited December 06, 2003).]

alias
Member
posted December 08, 2003 12:21 PM
What effect does lowering the centerlink have on the car? Also, why would you want
to take anti-dive out of the car? Would
you spring the car any differently if you
removed anti-dive?

I am a rookie at a lot of this stuff and
any info you guys can give is greatly
appreciated.


NJantz
Member
posted December 08, 2003 01:53 PM
As far as the roll center, I have seen recommendations from 3-5". I drew the critical points of my front metric suspension in AutoCad and found out that the roll center was about 4.5" below the surface. This was not good so I looked for ways to change this. I decided to leave my upper ball joint the same, and changed the lower ball joint to Coleman's extended length adjustable chrysler ball joint with a spherical bearing. The part numbers are on the drawing if you are interested. This will allow my roll center to be around 3"-4.5" max. I drew several different balljoint combinations and this the best I came up with.

As far as which one should you use. The end result is all the same, it doesn't really matter, You are trying to increase roll center, that is the point. But, you don't want to run too much angle on your arms and run out of spherical movement inside the balljoint cup.

The first thing you should do is utilize the software where you type your measurements into or draw a scaled version of your scenario. If you don't have cad software, you could make you some cardboard replica depicting your suspension. Please don't just change the roll center because Joe Blow racer did his, figure out where yours is at before you go out and change it. And why do you want to change it in the first place?

On the reason for removing anti-dive, you'd change this if you wanted to alter the handling of the car while getting on the brakes, most typically on corner entry. More anti-dive will not allow the front suspension to compress under braking. Pro-dive will. Pro-dive will tend to decrease the car's rear traction under braking by accepting the transferred load from the rear of the car. You can also make the car have pro-dive on the left front and anti-dive on the right front. This will make the right front carry the load transfer. It's kind of a driver feel thing on what you want the car to feel like on entry under braking.



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