I keep seeing everyone talking about wheel dimensions in terms of "offset". Wheel manufacturers do not use offset to talk about how they build their wheels.

They use backspacing.

I understand the '05 uses 5x4.5" bolt pattern wheels, and that the offset is "45mm on the factory 17x8 rim." Okay, fine.

I want to fit a set of 17x8s up front, and 18x9.5s in the rear. I want them to be 1/2" in from a plumb line dropped from the edge of the fender flare. All I need to know is what BACKSPACING to order these wheels in. I don't have a car to measure off.

Yet.

If you have any pics of specific wheels on cars that fit about like that, and the specifications on those wheels, that would be helpful. Thank you.
Danny

 

An 8" rim with an offset of 45mm, comes out to about a 5.77" backspacing, or in millimeters it is 146.6mm backspacing. Somebody correct me if I am wrong, but these are almost exactly right. Later.

-Andy

 

Actually, I measured it and it is right at 6 and 1/4 inches. I think you forgot to consider the width of the lip in your calculation. Offset does not vary based on thickness of the rim lip while back spacing does.

The Boss Hog

Edit: I should clarify that I measured my wheels which are the "Concept" wheels. I do not know the back-spacing on the Bullitt wheels.

 

You are right. The 2005 Wheels shown on page 8 are listed as having 5.295 back spacing. But you might want consider these four things:

1.) Wheels show are not the stock wheels.
2.) The stock wheels have 6 & 1/4 inch backspacing. If you don't believe me, measure them for yourself. It is very easy to do.
3.) Mathmatically there is no way an 8 inch wide rim can have both a +45 mm offset and a 5.295 backspacing. Sorry, ain't happening.
4.) If those wheels truely have the listed backspacing then they will stick out one inch more than stock. If that's what you want, great, but its still not stock.


The Boss Hog

 

http://www.bigcustomwheels.com/info_specs.jsp

Try this link...you may find it helpful in determining backspacing.

 

45 mm offset, means the mounting surface of the wheel is 45 mm from center of how wide the wheel is

 

and the wheel lip is not considered when you measure width or backspacing...

 

If that's what you want to believe, great. It is after all a free country.

The Boss Hog

 

If that's what you want to believe, great. It is after all a free country.

The Boss Hog
[/b][/quote]


go measure your rim from outside lip to outside lip and tell me what you get


wheel width measurements are based off of bead location, not overall width, it even shows that in your linky "boss"

 

Correct, the Lip is NOT included in width, I worked at discount tire for a while and when we measured wheels for balancing we never measured the lip.

 

go measure your rim from outside lip to outside lip and tell me what you get


wheel width measurements are based off of bead location, not overall width, it even shows that in your linky "boss"
[/b][/quote]

05GT,
I'm not interested in getting into a "contest" with you, but . . . .

"wheel width measurements are based off of bead location" is a true statement, but the original poster was asking about the back-spacing of the '05 Mustang wheels, not the wheel width. I have measured it and I did provide the measurement ("...right at 6 and 1/4 inches"). And yes, it is effected by the thickness of the rim's lip.


The measurement of Back-spacing does not reference either of the two bead location points used to determine wheel width. Back-spacing is strictly the distance from the wheel mounting plane to the plane defined by the furtherest outside edge of the rim lip on the backside of the wheel. The distance between that far outside rim lip edge and the adjacent "bead-location-point" on the inside of the rim lip is in fact the thickness of the rim lip. You can also determine the thickness of the rim lip by subtracting the wheel width (as determined by the bead location points) from the overall width of the wheel (from outside edge to outside edge) and dividing the answer by two.

For an '05 Mustang wheel with stock width (i.e. 8 inch ) and stock offset (ie +45 mm), the wheel with the thickest rim lip will have the largest backspacing.

The "Boss" Hog

PS the link (provided by KansasCityTim) is a good one. I suggest you look at it again.

 

ok I'm totally confused about all this stuff still. I went to that bigcustomwheels site and entered in this info:

The left/factory

235/55/17 17/8.0/45


The right/what I want

275/40/18 /18/9.5/25

The backspacing ends up being the exact same which is 6.2"

Does this mean that this wheel would fit right? I would figure that it would extend passed the lip with this low of an offset

 

 

Stangfriik,
Just compare the left side to the right side of the picture you posted and you will have your answer. With equal backspacing, the inside edge of the wheels will ride at the same location relative to the mounting surface. But, because the new wheel is 1 and 1/2 inches wider, the outside edge will stick out 1 and 1/2 inches more than stock. If that's OK with you then yes, it will fit.

When I purchased 9 and 1/2 wide wheels for my drag radials, I got them with almost 7 inches of back-spacing which is about 3/4 inch more than stock. This means mine stick in 3/4 inch more than stock and stick out 3/4 inch more than stock.

The decision is really up to you.

The Boss Hog

 

I also looked in the Ford Racing Parts spec for a 2005 17x8 bullitt wheel, the backspacing is 5.295" , which would equal a +20 mm offset.
What is correct , is this the 05' stock wheels, is this a performance wheel for a wider track?

I did find the weight of the 04 bullitt to be 25lb off that web site .

I'm with the Boss when measuring backspacing.

 

I really have no idea why those wheels are listed for the '05 Mustang. The stock wheel has +45 mm offset so, if that is not a misprint , those wheels will stick out an extra inch.

To each their own . . . . .

The Boss Hog

 

Would anyone know the offset on the 18" wheel Ford is planning on offering as an option for their 2006 model?

thanks.