Offset and backpsacing
9/16/04, 11:25 PM
#2
Backspacing and offset are related. Offset is the distance from the mounting plate on the wheel to the centerline of the wheel/tire. Backspacing is that same point measured to the very inside edge of the wheel.
Someone please correct me if I'm mistaken.
Anyways, 45mm offset on an 8" rim would be the same as 5.77" backspacing on the same rim.
8"/2 = 4" (inner edge to centerline) = 102mm + 45mm (offset) = 147mm = 5.77"
Someone please correct me if I'm mistaken.
Anyways, 45mm offset on an 8" rim would be the same as 5.77" backspacing on the same rim.
8"/2 = 4" (inner edge to centerline) = 102mm + 45mm (offset) = 147mm = 5.77"
9/16/04, 11:50 PM
#3
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If i got a 10 inch wide rim would i still need the same offset/backspacing, or would i need more?
If I get correct bolt pattern and backspacing for the 05 it will fit even if it doesnt say its offset.?
The wheels I want only have bolt pattern measurments and backspacing, they dont give offset.
If i know the Backspacing can I figure out the offset?
I know this is alot, but its just an empty space of knowledge which i dont have, and would like to be enlightened to feel complete for now. Thank you so much
Enfynet thank you for your informative post.
If I get correct bolt pattern and backspacing for the 05 it will fit even if it doesnt say its offset.?
The wheels I want only have bolt pattern measurments and backspacing, they dont give offset.
If i know the Backspacing can I figure out the offset?
I know this is alot, but its just an empty space of knowledge which i dont have, and would like to be enlightened to feel complete for now. Thank you so much
Enfynet thank you for your informative post.
9/17/04, 07:36 AM
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I think you're question was answered, but I'll paraphrase.
If you have a 10" wheel, you can have:
A) the same offset (which in effect makes the dish deeper, as it's more negative offset relatively since the wheel is now 10" vs 8" wide, but the same distance from the mounting plate to the rear edge) which will push the extra 2" of width to the 'outside' of the car, meaning it could hit the fenders if they don't provide enough clearance....or be really ghetto.
B ) more positive offset, which will move the mounting pad (backside of where the lug nuts go) closer to the centerline of the new, wider wheel (5" on center, instead of 4"), which will put more of wheel width to the inside of the car, meaning it could hit the inner fender housing, shock absorber, spring, frame rail, exhaust, etc. etc.
C) split the difference and measure carefully, you can be effective in centering the wheel in the housing over the hub and have enough clearance on the inside and outside
When you go that wide, you need to measure very, very, very carefully, because once you mount the tires, the rims are typically yours.
You can contact some wheel manufactureres as well, but if you get the numbers, you should be able to get a rough idea of what your limitations are before you start hitting stuff. Reread Enfynet's post, his arithmetic should get you where you need to go, just use some algebra and back in the numbers you need. First, you really need the car to make sure you're not going to rub anywhere.
Josh
If you have a 10" wheel, you can have:
A) the same offset (which in effect makes the dish deeper, as it's more negative offset relatively since the wheel is now 10" vs 8" wide, but the same distance from the mounting plate to the rear edge) which will push the extra 2" of width to the 'outside' of the car, meaning it could hit the fenders if they don't provide enough clearance....or be really ghetto.
B ) more positive offset, which will move the mounting pad (backside of where the lug nuts go) closer to the centerline of the new, wider wheel (5" on center, instead of 4"), which will put more of wheel width to the inside of the car, meaning it could hit the inner fender housing, shock absorber, spring, frame rail, exhaust, etc. etc.
C) split the difference and measure carefully, you can be effective in centering the wheel in the housing over the hub and have enough clearance on the inside and outside
When you go that wide, you need to measure very, very, very carefully, because once you mount the tires, the rims are typically yours.
You can contact some wheel manufactureres as well, but if you get the numbers, you should be able to get a rough idea of what your limitations are before you start hitting stuff. Reread Enfynet's post, his arithmetic should get you where you need to go, just use some algebra and back in the numbers you need. First, you really need the car to make sure you're not going to rub anywhere.
Josh
9/17/04, 07:47 AM
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You guys are pretty close, HOWEVER... don't confuse stated rim width (as measured from inside bead to inside bead), with TOTAL rim width. When you measure backspacing, you must work from total rim width to calculate offset.
An 8" wide rim measures 8" from inside bead to inside bead. If the mounting surface is centered within the wheel, it has "zero offset". The TOTAL width of the wheel (from outside edge to outside edge) will be close to 9" on an "8inch" wheel. The backspace measurement is from the very outside edge of the wheel, including the wheel rim "lip", which is typically ~1/2 per side. Therefore, an 8" wide rim with 0 offset, typically measures 4-1/2" backspace...
Handy chart to convert backspace to offset:
An 8" wide rim measures 8" from inside bead to inside bead. If the mounting surface is centered within the wheel, it has "zero offset". The TOTAL width of the wheel (from outside edge to outside edge) will be close to 9" on an "8inch" wheel. The backspace measurement is from the very outside edge of the wheel, including the wheel rim "lip", which is typically ~1/2 per side. Therefore, an 8" wide rim with 0 offset, typically measures 4-1/2" backspace...
Handy chart to convert backspace to offset:
9/17/04, 10:52 AM
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Right on...I was just too lazy to bring that into it. In fitting my 69 with 18x10" A/R TTII's, I have to fit for an 11" wide rim...then take into consideration also the actual section width of your tire, and diameter...etc. etc. Which is why you really need the car to make the determination. Getting the offset right is only the beginnning!
Josh
Josh
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