Math help

willowbilly3 · Post by **willowbilly3** » Mon Jan 30, 2006 9:38 pm

OK some of you guys who remember the equation. I need to set the cross member in my hotrod at 7 degrees. If the crossmember is 3 inches wide then how much in inches off level should it be?
I think 3 inches would be the diameter so 3 squared times pi (29.76) divided by 360 (.0822) times 7=.5754
Did I do that right? Over 1/2 inch seems like a lot.

1970F250 · Post by **1970F250** » Mon Jan 30, 2006 9:45 pm

sorry i almost got a D in math.

HOWDY69 · Post by **HOWDY69** » Mon Jan 30, 2006 11:24 pm

Ok 23 people have read this post and no one has volunteered so I guess I will jump in. I understand the cross member is supposed to be at 7 degrees. Is that really width wise or is it 7 degrees length wise?

68F250 · Post by **68F250** » Mon Jan 30, 2006 11:27 pm

Hey I just got home!

That's a trig function. See if I got the diagram right for what you are describing:

bmerkley58 · Post by **bmerkley58** » Mon Jan 30, 2006 11:31 pm

You would take 3" times pie (3.14) which would give you 9.42" and this would be your circumference. Then take 9.42" and divide it by 360 and you get .026", then take that times 7 and you get .183" or approximately 3/16".
When you took 3" and squared it and took it times pie you came up with the square inches of a 3" diameter circle rather than the circumference, and that is why you came up with such a high number.

Bob

HOWDY69 · Post by **HOWDY69** » Mon Jan 30, 2006 11:32 pm

I agree with 68F250, if you are talking about twisting it 7 degrees.

19674x4 · Post by **19674x4** » Mon Jan 30, 2006 11:47 pm

i agree with that, i found your mistake when you came up with square root of 3 times pi.

HOWDY69 · Post by **HOWDY69** » Mon Jan 30, 2006 11:55 pm

I think Bmerkley58 needs to multiply his answer by 2 because 3 is the radius not the diameter. 2 times .183 is .366 which is about what you get using trig. The straight line from the trig calc will be a little shorter than the arc calculation using PI.

19674x4 · Post by **19674x4** » Tue Jan 31, 2006 12:09 am

HUH???????????????????

HOWDY69 · Post by **HOWDY69** » Tue Jan 31, 2006 1:02 am

Since one end of the cross member is held in one place while the other rotates 3 is the radius not the diameter
The circumference is 2 PI R = 2 x 3.14 x 3 =18.84

(18.84 / 360) x 7 = 0.3663 which is the arc of 7 degrees

The other method is more exact since you will probably not measure along the arc on the car but you have to know the sine of 7 degrees to do the calculation. It gives you the vertical line as shown by 68F250 0.3656.

It is shorter to walk in a straight line than around a circle.

Was that any better?

mrung0wa · Post by **mrung0wa** » Tue Jan 31, 2006 4:10 am

Wow!

I am impressed. I strongly believe that you Brothers should be on TV!

You guys know your sipherin' and gosinta's (you know 2 gosinta 8, 4 times).

I'm proud to be apart of this meeting of the minds!

Lawrence

willowbilly3 · Post by **willowbilly3** » Tue Jan 31, 2006 9:13 am

Thanks guys. I never took trig so I don't know the sine and cosine stuff.
In case you are wondering the 7 degrees is for the kingpin inclination. Most old buggy sprung Fords (like model As) had the front crossmember set at that.

mrung0wa · Post by **mrung0wa** » Tue Jan 31, 2006 1:36 pm

Isn't great that we learn new stuff here almost everyday!

And I thought that I was through with my book learnin'!

Lawrence

heep70 · Post by **heep70** » Tue Jan 31, 2006 1:40 pm

I agree with 68f250. I actually got 0.359999173"

7 tanget cosine x 3" = 2.97" x 12% = 0.359999173"

flyboy2610 · Post by **flyboy2610** » Tue Jan 31, 2006 8:16 pm

I just read this thread.
Now my brain hurts!

The FORDification.com Forums

Math help

Math help

re: Math help

re: Math help

re: Math help

re: Math help

re: Math help

re: Math help

re: Math help