 Backspacing, what am I missing? |
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| McMark |
 Jun 25 2006, 06:30 PM
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#1
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914 Freak!  Group: Retired Admin Posts: 20,179 Joined: 13-March 03 From: Grand Rapids, MI Member No.: 419 Region Association: None  |
Somehow all of the "guides" for finding back spacing and offset don't seem to make sense between their examples and their formula.
This site for example. In their chart they list a 5.5 wheel with 3.75 back spacing as having a 12 mm offset. They say to find the offset that you subtract centerline (5.5 / 2 = 2.75) from back spacing (3.75). Which gives us (3.75 - 2.75) 1 inch. Which converts to 25.4 mm, NOT 12 mm. What I'm I missing? |
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Replies(1 - 5)
| Jeroen |
Jun 25 2006, 06:47 PM
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#2
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914 Guru Group: Members Posts: 7,887 Joined: 24-December 02 From: The Netherlands Member No.: 3 Region Association: Europe |
you're missing nothing... their table is just wrong
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| McMark |
Jun 25 2006, 06:51 PM
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#3
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914 Freak! Group: Retired Admin Posts: 20,179 Joined: 13-March 03 From: Grand Rapids, MI Member No.: 419 Region Association: None |
WTF, that's the SECOND site I've seen with BS info. (IMG:style_emoticons/default/confused24.gif) (IMG:style_emoticons/default/mad.gif)
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| Trekkor |
Jun 25 2006, 07:07 PM
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#4
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I do things... Group: Members Posts: 7,809 Joined: 2-December 03 From: Napa, Ca Member No.: 1,413 Region Association: Northern California |
Welcome to the internet (IMG:style_emoticons/default/smile.gif)
Didn't someone say, "Just because it's on the internet doesn't make it true"? KT |
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| pupwag |
Jun 25 2006, 07:26 PM
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#5
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Newbie Group: Members Posts: 44 Joined: 19-March 06 From: ATL GA Member No.: 5,739 |
Might be that the 5.5 is bead to bead and backspacing is measured to the outside of the wheel rim.Offset is also from the outer edges at least on that diagram.That might account for most of the difference.
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| Demick |
Jun 25 2006, 08:58 PM
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#6
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Ernie made me do it! Group: Benefactors Posts: 2,312 Joined: 6-February 03 From: Pleasanton, CA Member No.: 257  |
pupwag has it right. A 5.5" wheel is 5.5" from bead to bead (rim width in their diagram). You cannot accurately determine backspace from offset by just knowing the bead-to-bead width. You need the overall wheel width. Without it, you can just approximate what the backspace is (or offset is). Which is exactly what that table does.
For the most part, I have seen the wheel flanges to be around 3/8" wide for an alloy wheel. Looks like their table assumes about 1/2" wide wheel flanges, which is where your missing ~13mm comes from. Demick |
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