Physics Help Forum Race car front and rear suspension roll centers

Sep 4th 2014, 10:43 AM   #1
Member

Join Date: Jul 2014
Location: KY
Posts: 41
Race car front and rear suspension roll centers

I have built a database that has several racing calculators in it to help me at the track and in the shop to setup a late model stock car.
I would like to be able to figure the front and rear suspension roll centers and roll angle. In a perfect world the roll angles would be very close if not the same.

The data needed to do this is in the attachment.
Attached Files
 front and rear suspension geometry measurements.pdf (257.8 KB, 13 views)

Last edited by bei77; Sep 4th 2014 at 10:51 AM.

 Sep 4th 2014, 01:20 PM #2 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,333 I took a shot at the front suspension geometry, and calculated a roll center that is 1.6" to the driver's side of center-line, and 4.89" off the ground. There's a typo in your data though: I think line 10 is supposed to be "lower A arm ball joint to ground" - please confirm. The geometry comes out per the attached figure - please check that this seems reasonable. As for the rear - if you have a panhard suspension my understanding is that the roll center is right in the middle of the panhard rod. Attached Thumbnails
 Sep 4th 2014, 01:40 PM #3 Member   Join Date: Jul 2014 Location: KY Posts: 41 Yes you are correct on the typo. Did you use excel? How did you do the diagram?
 Sep 4th 2014, 02:25 PM #4 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,333 Yes, I used Excel (good guess!). What I did was set up equations for each of the four suspension components, in y=mx+b form. Then calculated the intersection point for the upper and lower control arms, which defines the instantaneous center for each side of the car. Then determined the equation for a line from the middle of the tire contact patch on the left side to the left instantaneous center, and also for a line from the right tire to the right instantaneous center, and the roll center is the intersection point of those two lines. The diagram is in PowerPoint. I scaled the suspension components to 1/10 size.
 Sep 5th 2014, 11:58 AM #5 Member   Join Date: Jul 2014 Location: KY Posts: 41 Wow! Thank you, that didn't take long. Can you send me the spreadsheet and let me see what I can do with it?
Sep 5th 2014, 02:04 PM   #6
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Join Date: Jun 2010
Location: Morristown, NJ USA
Posts: 2,333
Here you go.
Attached Files
 RollCenter.xls (69.5 KB, 34 views)

 Sep 5th 2014, 05:59 PM #7 Member   Join Date: Jul 2014 Location: KY Posts: 41 Can you repost the spreadsheet? For some reason it tries to open as a php file. Thank you.
 Sep 6th 2014, 05:35 AM #8 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,333 Seems to be working just fine. It sounds like your browser is trying to save the web page itself. If you right click on the file name you can save the file, it's called RollCenter.xls. Then open with Excel.
Sep 8th 2014, 01:43 PM   #9
Member

Join Date: Jul 2014
Location: KY
Posts: 41
I got it downloaded and it works great. I tested it with a friend of mine that has a racing set up program. (won't share) :-(.

I have worked with the spreadsheet and have gotten it racer friendly. Take a look and see what you think.

I also added a rear roll center sheet.
Attached Files
 RollCenter.xls (228.0 KB, 31 views)

 Sep 8th 2014, 02:19 PM #10 Physics Team     Join Date: Jun 2010 Location: Morristown, NJ USA Posts: 2,333 Looks good! Just one comment/question about the rear roll center sheet - it looks like perhaps the panhard bar is not symmetric with respect to the car's centerline, but I only see data on the height of its ends off the ground, not position with respect to the center line of the car. The roll center is in the middle of the panhard bar's length, so if the bar is offset left or right from the center of the car so too will the roll center be offset. Last edited by ChipB; Sep 8th 2014 at 03:38 PM.

 Tags car, centers, front, race, rear, roll, suspension

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