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Old 07 August 2002, 02:09 PM   #1
Gevor
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Does anybody know how to convert mm to degrees when adjusting toe in/out. All of the alignment shops here use only degree values and none of them seems to know how to convert mm or ' to degrees..
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Old 08 August 2002, 11:39 PM   #2
JIM THEO
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Let's say you want total toe in 1mm which is 0,5mm per wheel.
If you have 16'' wheels, the diameter of the wheel is 16 times 25.4 mm = 406.4 mm. Calculate the angle of the wheel by taking the arc tangent of 0.5 divided by 406.4, this is 0.0705 degrees and in minutes 4.2 ( 004'). Its about the same for 17'' wheels.
Hope this helps you.
JIM
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Old 09 August 2002, 10:16 AM   #3
Gevor
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Hmm... So 0.5mm toe in for a 16 inch wheel is 0.07 degrees, right?
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Old 10 August 2002, 09:45 PM   #4
MTR
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Jim Theo,
Surely you need to use the radius of the wheel, not the diameter, as the wheel pivots approximately around an axis through its vertical centre line on the hub, not from the back edge of the wheel.

Although even this isn't strictly true as the wheel pivots on a arc away from the centre line of the suspension strut, but at the moment I can't remenber the term used to describe this.

So you would use 203.2mm as the radius giving a greater angle than that that you have stated.
I am not certain if my maths is correct, but with an arc of 0.5mm and a radius of 203.2mm it gives an angle of 0.14 degrees.
So you would need a combined angle of 0.28 degrees to give 0.5mm toe in per wheel.
I think.

Cheers MTR
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Old 11 August 2002, 05:18 PM   #5
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Yes that's true mate, your maths are correct !
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Old 11 August 2002, 05:28 PM   #6
dhorwich
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what if you have 19" wheels like me will i need to get the alignment set up again...???

Dan
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Old 11 August 2002, 05:39 PM   #7
Gevor
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Thanks a lot everyone. Funny, but all the elignment equipement here uses degrees instead of mm or minutes/seconds. Another thing, when you start doing the alignment, after choosing the car make and the model you usually enter the wheels size. After the alignment is done, when you get the results, they're usually in mm.... So, this means the programs automatically converts degrees to mm for the chosen wheel size. Isn't that weird?
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Old 11 August 2002, 05:50 PM   #8
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Dan,
No you don't need to get anything reset.
The angle of toe in remains constant irrespective of wheel diameter, but the measured distance of toe in in mm increases on a larger diameter wheel.

Cheers MTR
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Old 11 August 2002, 06:20 PM   #9
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phew..!!!

I kept getting flash backs of 'school' 'maths' 'geometry' by which point i had lost the plot, hated maths...!!

Thanks

Dan
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Old 15 August 2002, 05:59 PM   #10
lethargicman
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The math is all terriffic and everything, but you're forgetting to incorproate the additional size of the tire. The rims may be 16", but the extra 2 1/2" radius or so of rubber I imagine would make a difference. That's an extra 5" to your wheel diameter. So technically, wouldn't you begin measuring from 21", then converting?

-Jason
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Old 15 August 2002, 05:59 PM
 
 
 
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alignment, angle, conversion, convert, degree, degrees, inches, measurement, millimeter, millimeters, minutes, mm, seconds, toe, wheel


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