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Offsets 101

3K views 20 replies 13 participants last post by  gary jackson 
#1 ·
Got a request for wheel offset info, so I figure Ill just go on a roll here. Ive heard EVERY possible wheel related question I think, and 90% pertain to width and offset for some odd reason. Ill throw out the fundamentals here for ya, and you can work with it. Offset is simply the amount of spacing (for our cars in mm) from the center point of the wheel inside the barrel. Domestics just call it backspacing and do it in terms of inches. Offsets will be positive in most cases, so for xBs it is usually safe to assume if they dont put a "+" sign in front of the number, that it is still positive. The center point inside the barrel is referred to as "0" offset in which the rest is gauged. A positive offset in one in which the mounting surface of the rim (where itll sit flush to the hub) is closer to the front (outward part) of the rim, than the back. A negative offset, of course, is where that mounting surface is closer to the back of the rim.

I hope I havent lost anyone here. Now to start figuring out offsets, you have to have a basic knowledge of math (or a decent online calculator. i end up usually doing it in my head since i find it quicker and easier). In an inch, figure that is appx. 26 mm. When lookin at rim rize, you of course see width. To start to figure things out, do basic math.

If you have rim that is 17x8 25 offset (mine), how much more does it stick out than a rim that is 17x7 40 offset. Now just reason it out. Theres an inch difference between the two in width. Now in ALL cases, think of the rim as two halves. Half of the rim is inside, half of the rim is outside. Therefore, the rim will stick out 13 mm more than the previous rim, based on width alone. Now figure in that, PLUS the fact that the mounting surface is 15mm more inside the barrel, itll push it out that much more. Therefore, the rim is added up to be 28 mm closer to the outside of the fender than the previous rim. Now I know I may hvae lost someone here since Im not good at explaining, so heres a calculator that some may use.

http://1010tires.com/WheelOffsetCalculator.asp

To figure out inner clearance, you can do the same basic method. When figuring in the least amount of inner clearance, I use 7" wide and 42 offset as my basemark. (its ridiculously close to inner suspension).

Heres picture for those that arent following what offset really is yet:


Following? Now I know you may ask OMG OMG will this fit? Well to tell that, I need to know some things. Width of tire, offset, width of rim, rolled fenders, and drop that you run. Theres no exact perfect way to tell on ALL accounts. On most I can give a 99% guess, but some I cant. On 17x8 25 offset I was rubbing becausse of a huge drop. 15x8 0 offset might not because of a small drop. I can give a good guess for most. Offset will depend on what look you want to achieve (VIP being the most aggressive aside from widebody and flares).

It boils down to some basic math and some udnerstanding of how things adversely will add or subtract. Now I know I may have lost some of you on this, and I apologize. Im just trying to give a basic understanding on this. Worst comes to worst, people can continue PMing me and I can answer things. With that said, I hope this helps! (sorry for the long windness and confusion)

Scotty
 
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#2 ·
I also want to add, that there are varying levels of "flush" and theres no exact answer. It helps to know what look you want to achieve and all. VIP flush is different from sporty flush. Oh and to clear up most questions relating to it. 7" wide wheel, from +20 offset to +40 offset wont rub. lol

Scotty
 
#6 ·
We do have an unofficial wheel size and offset chart, I think in the wheels section.

Scotty! Way to go man!

Basically, in layman's terms, the higher the offset number (positive) the closer to the outside edge of the wheel the lugs sit.

The lower the offset (negative) the fatter the lip you get, the closer the lugs sit to the inside edge.

Since sportmax is a company we're all familiar with, think about the 501's. They come in a +15 and a +38. The +15 gives a larger lip since it's only 15mm from the center of the wheel. The +38 is thus +23mm closer to the outside edge, giving less of a lip. Having the +38 on the front and +15 on the back gives a sweet staggered fitment on the lips, though you would need a spacer in the front....
 
#7 ·
Good start, Scotty! :)

Here's another image that might help...



It compares the small differences between my OEM tires and wheels with the After Market tires and wheels I put on Vanilla, but it labels and shows where the terms/measurements all come from. Hope it helps someone. :D
 
#8 ·
No problem guys! Im not a particular fan of wheel charts, because in the end noobs still ALWAYS ask if something fits. Happens on the other site even with it. ( I saw TG posted it here to). Plus, with so much individuality in suspension, tires, and wheels it is hard to have an exact match. People are bad about inferring then to their setups. I have a feeling no matter what chart we have, people will post up, but maybe this will help out anyway. If you have any more questions, dont be afraid to ask!.

scotty
 
#19 ·
It is a good start at an explanation, but you kind of glossed over, or missed a couple of things. First, you kind of missed that offset is the measurement from the center of the barrel or hoop to the mounting surface of the wheel. You kind of caught it as you continued, but the sentence describing it is a bit of an incomplete thought.

Second, there is a significant difference between backspacing and offset. While the two are relative, they are not the same thing. As was mentioned, offset is measured from the center of the barrel or hoop to the mounting surface of the wheel. Backspacing is measured from the back of the barrel or hoop to the mounting surface of the wheel. If you know wheels, it is very easy to do the conversion between offset and backspacing.

This leads to my next point. You rounded off the conversion from mm to inches as 26. In reality the number is 25.4. I know it might be nitpicking, but it does make a difference. It could mean the difference between rubbing and not rubbing for someone. It is all math in the end, so we might as well be accurate.

And my final comment is one that I do not think was addressed at all. What most people don't know about wheel sizes is that the actual width of a wheel is one inch more than the stated width. So a 17x7 is actually 8" wide, and a 17x8 is actually 9" wide. This doesn't matter at all to most people, but it is extremely important when doing conversions from backspacing to offset. It is also extremely important for folks who want to take measurements for clearance.

I hope I am not stepping on any toes here. I just wanted to throw in my two cents. I just felt like a bit of clarification and accuracy would be useful to those who actually want to make use of the information in this thread.
 
#20 ·
Some good points. I could have thrown in actual width vs. mounting width, but noobs have WAY too many damn problems with this anyway. The reason I didnt get into backspacing in more depth and more detail, is the fact that our cars deal only with mms. (unless it's something stupid like Intro Wheels :p)

Again, Ill reiterate the fact that this is a basic description. I recieve about 15 PMs per day, and most pertain DIRECTLY to this. Hope this helps some though!
 
#21 ·
Got a request for wheel offset info, so I figure Ill just go on a roll here. Ive heard EVERY possible wheel related question I think, and 90% pertain to width and offset for some odd reason. Ill throw out the fundamentals here for ya, and you can work with it. Offset is simply the amount of spacing (for our cars in mm) from the center point of the wheel inside the barrel. Domestics just call it backspacing and do it in terms of inches. Offsets will be positive in most cases, so for xBs it is usually safe to assume if they dont put a "+" sign in front of the number, that it is still positive. The center point inside the barrel is referred to as "0" offset in which the rest is gauged. A positive offset in one in which the mounting surface of the rim (where itll sit flush to the hub) is closer to the front (outward part) of the rim, than the back. A negative offset, of course, is where that mounting surface is closer to the back of the rim.

I hope I havent lost anyone here. Now to start figuring out offsets, you have to have a basic knowledge of math (or a decent online calculator. i end up usually doing it in my head since i find it quicker and easier). In an inch, figure that is appx. 26 mm. When lookin at rim rize, you of course see width. To start to figure things out, do basic math.

If you have rim that is 17x8 25 offset (mine), how much more does it stick out than a rim that is 17x7 40 offset. Now just reason it out. Theres an inch difference between the two in width. Now in ALL cases, think of the rim as two halves. Half of the rim is inside, half of the rim is outside. Therefore, the rim will stick out 13 mm more than the previous rim, based on width alone. Now figure in that, PLUS the fact that the mounting surface is 15mm more inside the barrel, itll push it out that much more. Therefore, the rim is added up to be 28 mm closer to the outside of the fender than the previous rim. Now I know I may hvae lost someone here since Im not good at explaining, so heres a calculator that some may use.

http://1010tires.com/WheelOffsetCalculator.asp

To figure out inner clearance, you can do the same basic method. When figuring in the least amount of inner clearance, I use 7" wide and 42 offset as my basemark. (its ridiculously close to inner suspension).

Heres picture for those that arent following what offset really is yet:


Following? Now I know you may ask OMG OMG will this fit? Well to tell that, I need to know some things. Width of tire, offset, width of rim, rolled fenders, and drop that you run. Theres no exact perfect way to tell on ALL accounts. On most I can give a 99% guess, but some I cant. On 17x8 25 offset I was rubbing becausse of a huge drop. 15x8 0 offset might not because of a small drop. I can give a good guess for most. Offset will depend on what look you want to achieve (VIP being the most aggressive aside from widebody and flares).

It boils down to some basic math and some udnerstanding of how things adversely will add or subtract. Now I know I may have lost some of you on this, and I apologize. Im just trying to give a basic understanding on this. Worst comes to worst, people can continue PMing me and I can answer things. With that said, I hope this helps! (sorry for the long windness and confusion)

Scotty
looking at konig 15x6.5 4x100 mm offset 40mm is konig a decent wheel 2006 xb
 
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