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Old 02-18-2010, 08:42 PM   #1
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Lightbulb Roll center on a pan car

How do you measure that on the front suspension? ...And maybe the rear to?
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Old 02-19-2010, 04:46 AM   #2
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Front:

Draw a line rectangular to the Kinpin through the lower pivot. Now draw a line trough the upper pivotball with the angle of the upper arm. Where both lines come together is the rollcenter height.


Rear:
Draw a line trough both pivot (T-Bar or Link). Extend the line to the ear axis and you have it.


Correct me if I'm wrong
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Old 02-21-2010, 04:23 PM   #3
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My correction...

The rear roll center is the height of the rear pivot ball - link or T-bar.

The front roll centre is effectively this. Draw a horizontal line parallel to the ground that goes through the centre of the lower pivot ball. For the right hand wheel, draw that line extending to the left. Now draw a line between the centre of the top ball, and the centre of the hinge pin, of the upper wishbone. This line will angle downwards. Where these two lines cross (somewhere to the left) join this point to the centre of the right hand tyre. Repeat for the left hand wheel.

Where the two lines from the intersection to the centre-line of the tyre cross (on the centreline of the car), is the instantaneous roll centre. Note that the roll centre moves side to side, and up and down, as the car rolls.

This diagram might explain it better than I did above! (Click on 'Suspension' and go to page three of that section for the diagrams.)

I said effectively. For suspension aficionados, this is not strictly correct due to the suspension design of the dynamic front ends on 12th cars. For any practical purpose, it works just fine. HTH
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Old 02-21-2010, 04:40 PM   #4
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Quote:
Originally Posted by Der Dicke View Post
Front:

Draw a line rectangular to the Kinpin through the lower pivot. Now draw a line trough the upper pivotball with the angle of the upper arm. Where both lines come together is the rollcenter height.
No, that's the instant center. To find the roll center, draw a line from the center of the tire's contact patch through the instant center. Where that line crosses the center line of the car is the roll center (more or less).

I suspect that to get it exactly right, you would use the methods for finding it on a strut suspension, just sort of flipped upside down.
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Old 02-21-2010, 05:27 PM   #5
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Quote:
Originally Posted by wingracer View Post
No, that's the instant center. To find the roll center, draw a line from the center of the tire's contact patch through the instant center. Where that line crosses the center line of the car is the roll center (more or less).

I suspect that to get it exactly right, you would use the methods for finding it on a strut suspension, just sort of flipped upside down.
For roadcourse cars you can use just one side and stop at the centerline of the chassis to get the front rollcenter. This is not the case for oval cars
(or any car that doesn't have the same geometry from right to left)


The rear rollcenter for all of the popular kits is exactly the center pivot for a link car and approximately the rear pivot for t-bar cars (flex changes things a little).
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