Wheels: Offset, Backspacing, & Wheel Spacers

[ExplorerDMB]

Offset and Backspacing

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.

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:

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:



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.



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.

-Drew

[ExplorerDMB]

Wheel Spacers

Wheel Spacers are simply what they are called - spacers. they create clearance/space between the wheel and the hub (mounting spot) which increases clearance from the inner wheel well. Most manufacturers use high-grade aluminum, which lead many to having weight and tire size rated spacers.

Adding wheel spacers will have the effect of running a wheel with a negative offset. they give you room for larger tires, thus solving most fitment issues. However, there is a downside; increased stress on the wheel bearings, spindles, knuckles, etc just like wider wheels or negative ofset. Also, remember that because of the fact that the spacers bolt onto the hub and then the wheel bolts to the spacer, this will cause you to have to torque 2 times more than usual. DO NOT FORGET TO TOQUE ALL THE WHEEL LUGS. The most important thing to remember when purchasing spacers is to carefully measure things out ahead of time so that you can purchase spacers that are no thicker than they have to be.

-Drew

[RangerX]

Excellent! We've needed this for a long time!

['97 V8]

nice article

[Mista808]

Yeah and even morons like me can understand it... kinda sorta LOL

[justin146]

This is 20x8.5 with +35mm offset. These pictures are without my spacers. I am currently running 1.5" hub-centric spacers on the rear.

[ExplorerDMB]

I added the wheel spacer section. Hopefully that'll help people as well. Thank you Section525 for fixing my issue.

-Drew

[Brett]

Great Article!

[mrprerunner]

I just ordered a front set of 2" spacers and a rear set of 1" spacers for my '93 from Motorsport Technology www.motorsport-tech.com . after installing the 4" superlift kit and putting 33"s on with hannemans glass, the front doest sit wide enough for my taste. i'll post pics in a couple of days when they arrive.

[ExplorerDMB]

added the "offset calculator" to my origional post : http://marksink.com/tire_wheel_offset/offset.html

-Drew

[Doubt Incarnate]

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

im confused, if i look at the picture, it looks like it works if i divide the wheel width by 2 then subract the back spacing, or not. 8/2-3.25=19.05mm looks like im wrong. but your way, 8-3.25/2=60.325mm, either way im not seeing it. my face hurts! point out my error so i can finaly figure it out.

[93 x_SPORT]

Originally Posted by ExplorerDMB

However, there is a downside; increased stress on the wheel bearings, spindles, knuckles, etc just like wider wheels or negative ofset.

Right now my offset on my stock wheels is 0". If I get a set of 17x7.5 wheels (44mm offset) and add a 1.25" spacer my offset will still be 0". Will I still have any of the above mentioned problems?

edit: Current vehicle is a 1997 X Sport with 16" wheels.

[xman98]

very nice job done by both of you. subscribing just so i always know that i can refer back to this thread when i need to!

[Shadow71]

Is there a list of the stock wheel sizes and tires.

I know the for STs for 05 the XLS and XLT have 29 inch tires that are 235/70-16

The XLT Premium and Adenalin have 30 incher, 255/70-16.

But I can't find the wheel size and offset anywhere.

[Dr G]

Originally Posted by Shadow71

Is there a list of the stock wheel sizes and tires.

I know the for STs for 05 the XLS and XLT have 29 inch tires that are 235/70-16

The XLT Premium and Adenalin have 30 incher, 255/70-16.

But I can't find the wheel size and offset anywhere.

I 2nd that!

[joshua_tree]

ok all i need to know is this....96 2dr, stock suspension, what is the largest wheel and tire i can fit on it....i have seen explorers similar to mine that didnt sit much higher than stock, and had a stuffed in tire look....thats what im going for so i would really appreciate if someone could help me out! thanks

[93 x_SPORT]

Originally Posted by joshua_tree

ok all i need to know is this....96 2dr, stock suspension, what is the largest wheel and tire i can fit on it....i have seen explorers similar to mine that didnt sit much higher than stock, and had a stuffed in tire look....thats what im going for so i would really appreciate if someone could help me out! thanks

http://www.explorerforum.com/forums/...d.php?t=153710

[1bad98sport]

im pretty surprised that a list of factory wheel size, width, offset/backspacing isnt availablefor our explorers. but im assuming if 93X_sport's 97 explorer sport came with 16" wheel with a zero offset, then they are 16x7 with a 3.5" backspace. then it would also be safe to assume the 15" wheels are the same as well(7" wide x 3.5" bs).....
knowing this we can order wheels with widths & offsets getting the wheels to sit exactly where we want them. im into the sport look(street/sport, not offroad) so i want my wheels to sit exactly flush with the fender lips on my 98 explorer sport(flared fender lips).....BUT dont forget to include the tire width in your equation if your calculating for the best fitment. the wider sidewall sticks out further so if you figure your wheel width to your fender lip you will most likely hang out past your fender lip a bit with the tire.....
im looking into this setup currently. (4) 18x9.5 wheels with 20mm offset(5.5" bs). this will allow the front to sit flush with the feder lip but i will need to run at least a 1" adaptor in the rear to even up the stance as a -5mm(4.5" bs) is not available in this particular rim im want. yes the rim/tire will be extremely close to the front suspension so tire choice will have to be calculated carefully....
basically i was unloading my thoughts on wheel choice here but mainly wanted to point out that if 93x_sport is correct with his offset calculation then it is safe to assum that our factory wheels are 7" wide with a 3.5" bs or 0 offset.....i believe all the factory wheels are 15" or 16" diameter and are 7" wide. there could be some special wheel sizes for limited edt vehicles so that needs to be taken into consideration.......

[BonesDT]

First of all, I think there is some confusion here. The "width" of the wheel is not the distance from outside brim to outside brim. E.g. a 16" x 7" Explorer wheel will measure about 8" from brim to brim.

So now when we talk about "backspacing" are we still measuring from the mounting surface to the brim as shown in the first live picture (with the 90 degree ruler)? If that's the right way to measure backspacing, then a 16 x 7 wheel with 3.5" backspacing does NOT have zero offset. The wheel would actually be sticking out a little more than zero.

My other question is, I'm trying to determine if my factory Explorer wheels will fit my Dakota. I already know the bolt pattern of 5 lug/4.5" is the same. My Explorer wheels are labeled "16x7" but I know they are going to measure about 8" from brim to brim.

My Dakota's stock wheels (15x6) have about a 4.875" backspacing measured from the hub mounting surface to the brim.

Does anyone have the backspacing for these Explorer rims:

Picture of my Explorer Wheel
(I have the AW3293

[Dan Whitaker]

The wheel width is measured from inboard bead seat to outborad bead seat.
Not brim to brim.

If you measure the OD of the wheel from the outside of the brim outside of the brim it will be larger than the given wheel size as well.