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Author Topic:   Roll Center--confused?
jello
Dirt Roller

Total posts: 16
posted October 13, 2004 05:51 PM  
Does raising the roll center help the
car roll over more or keep it from rolling
over so much?? Any help or explanations
would be appreciated.

Also, what about moving it left or right??

smayo964
Dirt Maniac

Total posts: 194
posted October 14, 2004 05:19 AM  
If my memory serves me correctly, and your talking about your roll center along your panard/j-bar axis, raising the roll center will minimize the roll. But, this will only work solely for roll center if your raise both ends of the panard/j-bar. If you only raising the chassis end, you're now introducing a percentage of bite in wheel loading depending on your rearend geometry. As for the left or right, that is dictated by the length of your bar in relation to the center of your chassis and weight distribution. The more you bring it closer to the center, the more you'll allow the chassis to roll (I think that's right). Hope that helps.

NJantz
Dirt Forum Champ
Total posts: 755
posted October 14, 2004 08:29 AM  
Lowering the roll center will help the car roll over more which helps generate more side bite. The roll center is the axis of rotation for the car when the body rotates left to right. The lower you place the roll center, the longer the "torque arm" you are generating. Longer torque arm's give the chassis/body more leverage which produces more roll which makes the right side tires grip the track harder. Does all that make sense? The principal is the same as a torque wrench. The roll center on a torque wrench would be where the socket attaches. The torque arm would be the location you place your hand on the wrench. The point you position your hand around the wrench is where the force gets applied. The further you move your hand away from the socket(roll center) the longer the torque arm you produce. This helps multiply the force you are generating with your hand generating more leverage.

So back to the racecar....The weight of the chassis/body is the force that causes the car to roll. The chassis/body is the same thing as your hand turning a socket wrench.

The roll center on the racecar is the same thing as the point that rotates on a socket wrench.

Increasing the distance between the rollcenter(socket attachment point) and the center of mass of the chassis/body(where you stick your hand on the wrench handle) you create more roll(leverage) due to a large torque arm or lever arm.

Holy cow I hope all that makes sense.



NJantz
Dirt Forum Champ
Total posts: 755
posted October 14, 2004 08:30 AM  
Here is a good article about roll centers and how they apply to panhard bars. http://www.rpmnet.com/techart/panhard.shtml

Ego Racing
Dirt Forum Champ
Total posts: 724
posted October 14, 2004 08:30 AM  
The rool center is located between the two heims on your panhard bar. If you are using a J-bar it is in the center of the two heims as if the bar was straight. The more weight you put on the right side of the roll center the more it will allow the chassis to roll. This is why you use a j-bar or a shorty bar on a dirt car and a long bar on an asphault car. You want roll on dirt and not on asphault.

rdirt
Dirt Full Roller

Total posts: 32
posted October 14, 2004 09:28 AM  
I've heard many time the roll center is between the two heim joints. This is isn't true. The roll center for all practical purposes is located on the same plane as the heims.
It could be located to the right of the heim of a shortlink. (looking from the rear)
or at about the same location as the pinon heim of a J-bar.
On a long panhard bar it will be located to the left of the axle mount heim.
That is why raising the chassis mount on a shortlink tightens the car and raising the chassis mount on a long bar loosens the car.

MikeN
Dirt Full Roller

Total posts: 27
posted October 14, 2004 12:58 PM  
rdirt,

Raising the chassis mount on a long bar tightens up the car. It's from the increased angle on the bar.

jello
Dirt Roller

Total posts: 16
posted October 14, 2004 05:39 PM  
thanks for the responses. I guess I should
of mentioned I was talking about the front
end, but I am guessing it works the same
on both ends of the car.

and yes NJantz, that made good sense, thanks
again for your help.

NJantz
Dirt Forum Champ
Total posts: 755
posted October 15, 2004 12:08 PM  
yep jello, the same theory's apply.

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