Home  |  Forums  |  914 Info  |  Blogs
 
914World.com - The fastest growing online 914 community!
 
Porsche, and the Porsche crest are registered trademarks of Dr. Ing. h.c. F. Porsche AG. This site is not affiliated with Porsche in any way.
Its only purpose is to provide an online forum for car enthusiasts. All other trademarks are property of their respective owners.
 

Welcome Guest ( Log In | Register )

> alignment math, all you numbers guys check my math!!
jaybird840
post Jan 4 2008, 02:11 PM
Post #1


Member
**

Group: Members
Posts: 163
Joined: 27-September 06
From: Austin, TX
Member No.: 6,927
Region Association: Southwest Region



OK,

I'm working on a home alignment on my teener, and am trying to calculate my camber adjustments. I can't use the bird board measurements because I'm running 18" wheels. So, in order to get an adjustment measurement, I calculated the circumference of my wheels--outer lip to outer lip (this is where I take my measurements). C=diameter x pi--right? So if my wheels measure 19.5", then the circumference = 19.5 x 3.14159 which gives a circumference of 61.26". If you divide the circumference by 360, then 1 degree = .17". In order to run 30" of negative camber, I divide by three again to give me .05" or 1.43mm. Now, in order to achieve that number, I must multipy by two to get the actual measurement from the bottom of the rim to the top of the rim, right? Long story short, my measurement needs to be 2.86 (call it 3mm) greater at the top of the rim than the bottom of the rim, right? I'm a cop, not a math genius, so you engineers feel free to chime in.... thanks tons!!!!!

While on the subject of alignments.... What should the toe in measurements be in degrees? Am I right that a 32nd on 15's is different than a 32nd on 18's?

--jaybird
User is offlineProfile CardPM
Go to the top of the page
+Quote Post
 
Reply to this topicStart new topic
Replies
jd74914
post Jan 4 2008, 03:03 PM
Post #2


Its alive
****

Group: Members
Posts: 4,782
Joined: 16-February 04
From: CT
Member No.: 1,659
Region Association: North East States



I am assuming you mean -3 degrees camber, but if not you can just change the numbers

I haven't read the bird board instructions, but in to start you off this page is very informative on tire alignments.

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=4

Now, going by what they have written you can use geometry to figure out the necessary difference. All you need to do is find the wheel radius which equals the wheel diameter / 2 (since the degree measure is from the imaginary central axis of the wheel perpendicular to ground and to the new central axis). Then you can use trig and do sin(3)*wheel radius = distance from imaginary center axis to new central axis.

To simplify this measurement you can measure the horizontal difference from the bottom of the rim to the top of the rim. All you need to do is double the distance difference I came up with (IMG:style_emoticons/default/smile.gif)

Using sin(3)*wheel radius (with your radius as 19.5/2 = 9.75) the horizontal difference from wheel center to top edge is .510 inches.

If you want to measure the horizontal difference from the bottom to top of rim you need .510*2 = 1.02 inches.

I added a quickly drawn picture to illustrate the geometry.


Attached thumbnail(s)
Attached Image
User is offlineProfile CardPM
Go to the top of the page
+Quote Post

Posts in this topic


Reply to this topicStart new topic
1 User(s) are reading this topic (1 Guests and 0 Anonymous Users)
0 Members:

 



- Lo-Fi Version Time is now: 10th June 2024 - 12:15 PM