Backspace = offset
Backspace = offset Can somebody convert my backspace measurement to offset,my math isn't working to good.
My backspace is 71/4
Thanks
Rocket
Oh yeah,I'm planning on 18x10's
My backspace is 71/4
Thanks
Rocket
Oh yeah,I'm planning on 18x10's
Last edited by rocket22; Sep 26, 2006 at 07:04 PM.
Approximately 44 mm . . . back space and offset are related, but not directly linked.
To accurately calculate the offset from the BS one needs to know how thick the bead is. By rull of thumb I use 1/2" as the bead thickness.
To accurately calculate the offset from the BS one needs to know how thick the bead is. By rull of thumb I use 1/2" as the bead thickness.
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Easy way to calculate offset from BS is:
1) Add 1" to advertised width of wheel to account for flanges
2) Divide that width by 2 to obtain centerline of wheel ("zero offset")
3) Subtract this quotient from the backspacing number you have to calculate the offet from centerline. (note that positive offset means the wheel center section is offset outboard and negative offset means the center section is offset inboard)
4) Convert the resultant from inches to millimeters if necessary (usually BS numbers are quoted in inches and offsets are quoted in mm - not really sure why that is).
EXAMPLE:
You want to calculate the offset on a 17x11 wheel with an 8.0" backspacing:
1) 11"+1" = 12" overall width
2) 12"/2 = 6"
3) 8"-6" = +2" (note that its positive in this case)
4) 1" = 25.4mm, so 2" = 50.8mm
ANSWER ==> +50.8mm offset, which can be rounded to +51mm
So, +51mm is equivalent to 8.0" backspacing on the 17x11" wheel.
1) Add 1" to advertised width of wheel to account for flanges
2) Divide that width by 2 to obtain centerline of wheel ("zero offset")
3) Subtract this quotient from the backspacing number you have to calculate the offet from centerline. (note that positive offset means the wheel center section is offset outboard and negative offset means the center section is offset inboard)
4) Convert the resultant from inches to millimeters if necessary (usually BS numbers are quoted in inches and offsets are quoted in mm - not really sure why that is).
EXAMPLE:
You want to calculate the offset on a 17x11 wheel with an 8.0" backspacing:
1) 11"+1" = 12" overall width
2) 12"/2 = 6"
3) 8"-6" = +2" (note that its positive in this case)
4) 1" = 25.4mm, so 2" = 50.8mm
ANSWER ==> +50.8mm offset, which can be rounded to +51mm
So, +51mm is equivalent to 8.0" backspacing on the 17x11" wheel.
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