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Topic: How do you figure out wheel backspacing if you only know the offset and wheel size
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166 Merlo
FELONY
MOTORSPORTS
Member # 1549
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posted
 
 
For example on this wheel right here:
(edit: well I guess you know both variables here, but lets just say you only knew the offset)
Chrome Saleen
if +28mm offset is about 1.1 inches, and half of 18x10 (wheel centerline) is 5" then why why isn't 5"+ 1.1"= 6.1" the backspacing listed on their website? BS listed: 6.6"
Does anyone follow? Am i making sense? Yarada-tadada?
i noticed this on a couple different sites, sometimes the math makes sense, but it usually doesn't. Please help thanks.
[ July 14, 2010, 05:23 AM: Message edited by: 166 Merlot ]
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Posts: 3953 | From: Thebay | Registered: Jul 2002
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SteveL
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Member # 1241
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posted
Because they are not measured from the same point.
Backspace is measured from the outermost lip of the rim in towards the hub mount. It includes the part of the rim that sits outside of the tire bead (which is typically 1/2" thick).
Offset is measured between where the tire bead sits which is inside the lips of the rim. A 0 offset 10" rim will have a backspace of 10/2= 5 inches + another 1/2" for the part of the rim that's outside the tire bead.
A 10" wide rim is actually about 11" wide. 10" is the distance between the tire beads and 11" is the overall width of the rim including the inner and outer lips.
[ July 14, 2010, 08:52 AM: Message edited by: SteveL ]
Posts: 578 | From: San Jose, CA | Registered: May 2002
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copcar
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Member # 10113
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posted
You forgot the 1/2" for the lip.
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12.37@ 109.34.NA 894DA Old Nitto 555 DR's Gt40 irons. B cam/1.7's, All emissions equipment on the car, stock air box. UPR catted X pipe.
Posts: 485 | Registered: Jun 2010
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166 Merlo
FELONY
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Member # 1549
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posted
Ok I see what you guys are saying, but what about this one:
Chrome saleen 2
math makes sense on this one? I found a wheel I like but the dude won't email me back as to what the BS is... I don't want to be off by even a 1/2" cuz I'm already pushin it on the clearance.
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'89 - Boss Coupe
'70 - Drop Cutthang
'68 - Cougnut
'87 - 0166, Its real
Posts: 3953 | From: Thebay | Registered: Jul 2002
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SteveL
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Member # 1241
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posted
It's 9" wide between the tire beads. Half that is 4.5" to the centerline. The offset is +0.9" so the mounting plate is 4.5+0.9 = 5.4" in from the inside tire bead. Assuming 0.5" for the lip so the backspacing is 5.9". The math works.
Regardless, you have a different problem. You found a rim. You don't know what it's backspacing is and don't know if it will fit. No one can answer that.
Posts: 578 | From: San Jose, CA | Registered: May 2002
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166 Merlo
FELONY
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Member # 1549
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posted
quote:
Originally posted by SteveL:
It's 9" wide between the tire beads. Half that is 4.5" to the centerline. The offset is +0.9" so the mounting plate is 4.5+0.9 = 5.4" in from the inside tire bead. Assuming 0.5" for the lip so the backspacing is 5.9". The math works.
Regardless, you have a different problem. You found a rim. You don't know what it's backspacing is and don't know if it will fit. No one can answer that.
I think you just did. Thanks for the help
![[patriot]](graemlins/patriot.gif)
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'89 - Boss Coupe
'70 - Drop Cutthang
'68 - Cougnut
'87 - 0166, Its real
Posts: 3953 | From: Thebay | Registered: Jul 2002
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68dustin
CAFords OG
Member # 5388
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posted
http://www.rimsntires.com/rt_specs.jsp
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"As I lay rubber down the street, I pray for traction that I can keep, and if I do begin to slide, please dear God protect me and my ride!"
Posts: 3986 | From: neverland | Registered: Feb 2005
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166 Merlo
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Member # 1549
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posted
quote:
Originally posted by 68dustin:
http://www.rimsntires.com/rt_specs.jsp
That's what's up right there. Got me a new bookmark. ![[Whoo Whooooo!]](graemlins/woowoo.gif)
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'89 - Boss Coupe
'70 - Drop Cutthang
'68 - Cougnut
'87 - 0166, Its real
Posts: 3953 | From: Thebay | Registered: Jul 2002
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