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Wheels: Offset, Backspacing, & Wheel Spacers

Offset and Backspacing

wheel_offset.gif

tech-wheelterms.gif

When you bought your vehicle from the dealership, engineers have put long hard hours to calculate a wheel and tire combo that would work well with the vehicle. Calculating width, diameter, offset, rear spacing, offset, and much more. Most people think; "The bolt patterns are the same, let's bolt them up." That is where people finally find a problem. Some may fit, some may not, and some will look unsightly. Anyhow, those engineers designed a wheel that would distribute load evenly on the wheel bearings, clear the rotors and braking system parts, and also keep you from rubbing your frame or front bumper. So, well, how do you figure out which works best and what is what - just tell me what I need and move on; right? Well, hopefully this thread will clear up some issues on wheels and how important some aspects of wheels are.

Backspacing is the distance from the inside bolting surface of the rim to the outer edge of the inboard side of the rim. Offset is the distance from the exact center of the rim to the outer edges of the rim. Positive offset means that the center of the wheel is moved towards the vehicle, while negative offset means the center of the wheel is moved away from the vehicle. Some images on the bottom will help figure this out.

wheel_offset.gif

In most cases, the factory wheels have positive offset (especially the new Explorers). Now most aftermarket wheels will have negative offset to push the wheel out further - reason being is to clear bigger tires and to keep you away from hitting frame, bumper, fender well, etc with your tires. The bad part is that there will be more load on the lugs, bearings, spindles, and even cause a larger turning radius. Also the tires will go past the fender well, which in some states can be illegal. Another good thing about negative offset besides clearing bigger tires is the imroved stability with being wider.

Measuring Offset and Backspacing:

33_body_backspacing1.gif

Backspacing is easy to measure. Place a straight edge across the wheel like above and then measure from the bottom of the straight edge to the mounting pad of the wheel. This will give you your backspacing measurments.

To calculate offset is even easier, measure the wheel's overall width, subtract its backspace measurement, and divide that by two. You're done.

Examples:

464729_152_full.gif


That picture is of my newest wheels (15x8s) with 3-3/4" backspacing and -19mm offset. That picture demonstrates how far the wheel is pushed out with that set up.

464729_51_full.gif


That picture is of the oldest setup which is 15x8s with 3.25" backspacing and -30 offset.



So if the backspacing is 3.25" and the offset is -30mm (-1.18 inches) and your wheel width is 8" then you have 3.57" of wheel that will stick out from where it mounts. It is a little complicated to understand, but it's simple once you do get the hang of it. Refer to the bottom for a picture. It is a rough estimate of what the measurments would look like with a wheel.


Use this to calculate MM to Inches and vise versa


NEW: Offset Calculator

Hope this helps a lot of people out. :thumbsup:

-Drew
 

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Tiny1234

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2004 Ford Explorer Limite
Please help I want to put A/R baja on my 2004 explorer limited do ineed spacers and if so how big.
 
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DoubleNickel

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2007 Explorer XLT
Will Stock 04 Wheels Fit a Stock 07?


Looking at a set of takeoffs from a 2004 Explorer (17" x 7.5). I've seen pictures of wheels that look just like these on a 2007 (see link). But I need to know if they are exactly the same or not. Will 04s fit exactly or will they'll rub/need spacers, etc.? Here's the link for identical-looking wheels on an 07:

http://www.edmunds.com/photoflipper/?year=2007&make=Ford&model=Explorer

The wheels are stamped 17X7.5 JX44

(If this post is out of place, please let me know where I should post it; and I apologize :)
 
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Ericb3

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2003 Explorer XLT
Hey y'all,
I'm still new, so if I can find the answer to my question somewhere already just point me in the right direction. But I'm wondering, will GY Wrangler 265/70R17 or Toyo Open Country A/T II of the same size fit my bone stock 2003 Explorer XLT? It has the 17x7.5 wheels and its RWD. No lift, no anything. I need new tires as mine are getting bald, and they are the stock size tires. So if I wanted to go up to those sized tires, would I need wheel spacers? Would I have to worry about scrubbing, both at full turn and with suspension travel? I do plenty of off roading and I need a larger, wider tire with more aggressive tread to get through the mud. So yeah, will those fit with no issues? If there are issues, what would they be?
 
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distinguishdgent

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2007 Sport trac xlt 4x4
Hello all. I have an 07 sport trac xlt 4x4. I am looking to upgrade my rims. I found some 17 x 9's that i like the look of. discount tire told me i would need at least a 255/60/17 tire. Can any one tell me how far out a 17x9 will stick out? I would like for the tires to stick out past the fender a little bit, without looking silly. i know nothing about rims and tires and would welcome any feedback. thanks!
 
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97cherbal

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grayghost1956: the F150 five lug should be 5 on 5.5 bp where as the Ranger/Explorer uses the 5 on 4.5 bp

J-bubba: I just transferred my 16x7 factory ford alloy wheels w/ 265/75/16 MT from my 94 Ranger to my 98 Explorer XLT. All I had to do with my explorer was remove the 6" section of the side skirt kit that is attached to the back section of each front fender. If you don't have the factory side skirts or factory fender flares then you shouldn't have any clearance issues.
 
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boski

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Offset and Backspacing

wheel_offset.gif

tech-wheelterms.gif

When you bought your vehicle from the dealership, engineers have put long hard hours to calculate a wheel and tire combo that would work well with the vehicle. Calculating width, diameter, offset, rear spacing, offset, and much more. Most people think; "The bolt patterns are the same, let's bolt them up." That is where people finally find a problem. Some may fit, some may not, and some will look unsightly. Anyhow, those engineers designed a wheel that would distribute load evenly on the wheel bearings, clear the rotors and braking system parts, and also keep you from rubbing your frame or front bumper. So, well, how do you figure out which works best and what is what - just tell me what I need and move on; right? Well, hopefully this thread will clear up some issues on wheels and how important some aspects of wheels are.

Backspacing is the distance from the inside bolting surface of the rim to the outer edge of the inboard side of the rim. Offset is the distance from the exact center of the rim to the outer edges of the rim. Positive offset means that the center of the wheel is moved towards the vehicle, while negative offset means the center of the wheel is moved away from the vehicle. Some images on the bottom will help figure this out.

wheel_offset.gif

In most cases, the factory wheels have positive offset (especially the new Explorers). Now most aftermarket wheels will have negative offset to push the wheel out further - reason being is to clear bigger tires and to keep you away from hitting frame, bumper, fender well, etc with your tires. The bad part is that there will be more load on the lugs, bearings, spindles, and even cause a larger turning radius. Also the tires will go past the fender well, which in some states can be illegal. Another good thing about negative offset besides clearing bigger tires is the imroved stability with being wider.

Measuring Offset and Backspacing:

33_body_backspacing1.gif

Backspacing is easy to measure. Place a straight edge across the wheel like above and then measure from the bottom of the straight edge to the mounting pad of the wheel. This will give you your backspacing measurments.

To calculate offset is even easier, measure the wheel's overall width, subtract its backspace measurement, and divide that by two. You're done.

Examples:

464729_152_full.gif


That picture is of my newest wheels (15x8s) with 3-3/4" backspacing and -19mm offset. That picture demonstrates how far the wheel is pushed out with that set up.

464729_51_full.gif


That picture is of the oldest setup which is 15x8s with 3.25" backspacing and -30 offset.



So if the backspacing is 3.25" and the offset is -30mm (-1.18 inches) and your wheel width is 8" then you have 3.57" of wheel that will stick out from where it mounts. It is a little complicated to understand, but it's simple once you do get the hang of it. Refer to the bottom for a picture. It is a rough estimate of what the measurments would look like with a wheel.


Use this to calculate MM to Inches and vise versa


NEW: Offset Calculator

Hope this helps a lot of people out. :thumbsup:

-Drew

This is a nice post but I notice some of the text is not correct. Offset is not the distance from the center of the rim to the edge of the rim. Offset is the distance from the center of the rim to the inside bolting surface of the rim. The calculation is also not correct. The calculation should be Offset = backspacing - 1/2 rim width. So for example with an 8 in wide rim, if the backspacing is 5 inch the offset is 5 - 4 = positive 1 inch. If the backspacing is 3 inch the offset is 3 - 4 = negative 1 inch.
 
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boski

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1998 XLT AWD 5L
This is a nice post but I notice some of the text is not correct. Offset is not the distance from the center of the rim to the edge of the rim. Offset is the distance from the center of the rim to the inside bolting surface of the rim. The calculation is also not correct. The calculation should be Offset = backspacing - 1/2 rim width. So for example with an 8 in wide rim, if the backspacing is 5 inch the offset is 5 - 4 = positive 1 inch. If the backspacing is 3 inch the offset is 3 - 4 = negative 1 inch.

The width in the post above is the total width from outside edge to outside edge. I should not have used the term rim width in the calculation. The rim width given in a wheel spec is maybe an inch smaller than the total width because rim width is the distance between the inside of the bead mounting surfaces. Backspacing is measured from the outermost surface of the rim. If you try to use the relation above between offset and backspacing you would need to use the total width of the wheel. It is easy to be confused since the spec given as rim width is not measured from the same surface as backspacing.

For example, if the rim width spec was given as 7 inches and offset is 0, the total width is probably around 8 inches. This makes the backspacing about 4 inches because that would be the distance from the outermost edge of the rim to the hub mounting surface which would be on the centerline of the wheel with offset being 0. Total width is not given as part of the wheel spec on websites. You could calculate the total width using the offset, rim width, and backspacing specs. It would be easiest if the offset was 0. Then the total width would simply be twice the backspacing.
 
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blueka

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I'm planning on putting the 5" RC lift on my explorer (pictured) in the next few months. This post has confused me quite a bit. I would like to move up to 18" wheels but also want them to sit a bit further out, as I'll be running 35s.

I'm currently running the stock 16s pictured and was wondering what offset/backspace I'm going to need..

Super confused.

Cheers

Si
IMG_20201115_000756 (1).jpg
 
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