I just wanna make sure my math is correct on backspacing. - Ranger-Forums - The Ultimate Ford Ranger Resource


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Old 04-05-2008
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I just wanna make sure my math is correct on backspacing.

If a rim has a backspacing of 4.75" but it has an offset of -6.6mm that is the same as saying the rim has 4.5" of backspacing correct? I figured this because it is a 9" wide rim so its 4.75" of backspacing however the hub has a negative offset of 6.6mm which comes out perfectly to .25". This to me says that the rims will technically have a 4.5" backspacing.
Thanks for the help.
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Old 04-05-2008
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sorry not quite....

if a rim has 4.75" backspacing it has -6.6mm offset.

4.5" is the center of the rim.
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Old 04-05-2008
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Okay..so like I figured Im confused..will these work? or should I go with the 17x8 4.5" backspacing?
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Old 04-05-2008
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I would go with 4.5, i am really not sure if 4.75 will clean the spindle. i dont know for sure.

offset is in direct relation to backspacing. so if the backspacing changes then the offset will change.

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Old 04-05-2008
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offset and backspacing are only slightly related in the fact that they both define the location of the mounting surface relative to width.

backspacing is backspacing, no matter what. it is a fixed measurement from the lip to the mounting surface. you can have two rims with the same backspacing BUT have different offsets based on the rim widths.
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Old 04-05-2008
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so that picture just cleared everything up for me. Wow I was so lost on the whole thing and now I know exactly whats I'm looking for. Thanks for that.
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Old 04-05-2008
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Okay...well thanks for straightnenin this out for me...I will def. go for the 4.5" backspacing. Thanks for the help!!
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Old 04-05-2008
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Quote:
Originally Posted by gumby View Post
offset and backspacing are only slightly related in the fact that they both define the location of the mounting surface relative to width.

backspacing is backspacing, no matter what. it is a fixed measurement from the lip to the mounting surface. you can have two rims with the same backspacing BUT have different offsets based on the rim widths.
Ah idk you will have to explain that to me later.

I understand what you are saying but i think they are directly related.
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Old 04-06-2008
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I just dont get why every single 6001 rim that pro comp makes has a 4.5" backspacing and then there is like a very few random ones (including the 17x9) that comes only in 4.75" backspacing. Whats the deal w/ that?
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Old 04-06-2008
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hi man, i will install my 17" procomp wheels in about 3 weeks with 33/12,5/17 baja claw radial tires on them. At this moment, i will be able to let you know if there is problems with my 4,75" BS 17x9 6007 wheels. There are in the garage since about 2 months but there is too much snow here in Quebec.
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Old 04-06-2008
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Originally Posted by zabeard View Post
Ah idk you will have to explain that to me later.
if they were directly related one would always increase/decrease in relation to the other.

now, take a look at your diagram. keep the BS the same, but make the wheel wider. when you make the wheel wider, you also hafta move the centerline. movin the centerline w/o adjustin the mounting location(fixed BS) changes the wheel offset.

they are measured from different points in such a way that they cannot always be directly related. especially when you figure that BS is measured from the backside lip and the centerline is an imaginary point between the tire mountin surfaces, completely disregarding the lip of the rim.

Last edited by gumby; 04-06-2008 at 10:54 AM.
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Old 04-06-2008
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Originally Posted by MathieuRoyer View Post
hi man, i will install my 17" procomp wheels in about 3 weeks with 33/12,5/17 baja claw radial tires on them. At this moment, i will be able to let you know if there is problems with my 4,75" BS 17x9 6007 wheels. There are in the garage since about 2 months but there is too much snow here in Quebec.
Dern man I wish you were installing them sooner!! I hope to have my lift/tires/rims complete by then. Either way post pictures when your done just incase I aint gotten mine yet..thanks!
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