Offset and Backspacing

http://www.robrobinette.com/images/wheel_offset.gif

http://www.rsracing.com/images/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.

http://www.arbabzadeh.com/~hooshnam/rim/wheel_offset.jpg

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:

http://www.ocmhz.com/images/33_body_backspacing1.jpg

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:

http://memimage.cardomain.net/member_images/8/web/464000-464999/464729_152_full.jpg

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.

http://memimage.cardomain.net/member_images/8/web/464000-464999/464729_51_full.jpg

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 (http://www.lambron.com/length.html) to calculate MM to Inches and vise versa

NEW: Offset Calculator (http://marksink.com/tire_wheel_offset/offset.html)

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

-Drew

http://www.rockcrawler.com/techreports/spidertrax_spacers/spacer5.jpg
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. :thumbsup:

-Drew

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

nice article

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

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.

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

-Drew

Great Article!

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 (http://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.

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

-Drew

"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! :confused: point out my error so i can finaly figure it out.

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.

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!

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.

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!

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

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/showthread.php?t=153710

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.......

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 (http://www.ackerwheel.com/wheels/genpage.php?make=Ford&model=Explorer&year=1999)
(I have the AW3293

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.

HI guys NEW Here. I have a ? 4 ya. I have a 2003 Ford Sport Trac and would like to install some new wheels and tires. The current wheels are 16x7 and if you measure like above from the back of the wheel to the back rim lip, I come up with 4.5inches. Now I would like to install 22x9.5 wheels and a 2" lowering kit in the front and a 3" in the rear. Just wondering what you guys suggest i get for a offset of wheel. I AM LOST.. Also I DO NOT want the wheel to stick out of the wheel well. Thanks guys.. Casey

Even I should be able to do this ..Thanks

I'd like to replace the wheels on my 06 Limited , can anyone tell me the factory 18" wheel offset ?
Thanks ,
Ronny

Sorry to bump this but are you saying that wheel spacers are bad or ok? I really want some but ifd they are dangerous then I don't. I can't be hauling around my family thinking my wheel might fly off.

I think you'll get mixed answers to that question.

If you want to go the safest route, get the spacers with their own lug bolts. This kind of spacer bolts onto your hub using your existing lug bolts, but then you need to chop off the excess length of the existing lug bolts and you install the tire with the new lug bolts welded to the spacers. The downside is that this is more permanent.

The cheaper spacers will just use your same lug bolts, putting stress too far out on the end of the lug bolts.

I think you'll get mixed answers to that question.

If you want to go the safest route, get the spacers with their own lug bolts. This kind of spacer bolts onto your hub using your existing lug bolts, but then you need to chop off the excess length of the existing lug bolts and you install the tire with the new lug bolts welded to the spacers. The downside is that this is more permanent.

The cheaper spacers will just use your same lug bolts, putting stress too far out on the end of the lug bolts.

Lug bolts (or wheel studs) do not take the weight of the wheel, the centre hub adapter does that (or should). Wheel spacers that do not have a machined lip to support the centre of the wheel will mean that you break wheel studs.

Lug bolts (or wheel studs) do not take the weight of the wheel, the centre hub adapter does that (or should). Wheel spacers that do not have a machined lip to support the centre of the wheel will mean that you break wheel studs.

Good point. I forgot about that. Definately a must when buying a spacer.

Come to think about it, I don't think my new American Racing wheels rest on the center hub! I should look into that.

The relationship between wheel back spacing and offset on here does not work for me when using numbers given by a website for any of their wheels.

bump

Anybdoy have any info on this?

Guess not, or we missed something... I think the Offset is half of the BS.. with some conversion?.. I don't know...

Guess not, or we missed something... I think the Offset is half of the BS.. with some conversion?.. I don't know...

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

The relationship between wheel back spacing and offset on here does not work for me when using numbers given by a website for any of their wheels.The important thing to keep in mind is that a wheel's backspacing and its nominal width are not measured to the same place. This is what usually causes the confusion.

Width is measured to the inside of the flanges where the beads seat.
Backspacing is measured from the outside of the inboard flange to where the wheel mounts.

As a rule of thumb, most wheel flanges are very close to 1/2" thick each. So the overall width of a nominal 7" wheel is about 8".



Example: The offset of a factory Gen 1 or 2 Explorer wheel is +12mm, close to 1/2".

To find the backspace dimension of a wheel with a 7" nominal width and +12mm offset, start with the overall width (7" + 1" = 8"), divide by two and then add the offset (8"/2) + 1/2" = 4 1/2"



Pictures of a wheel with same dimensions as in the above example. notice that the measurement is being taken from innermost part of the inboard flange to the wheel's mounting surface. This is where the overall width is about 8" as opposed to 7" where the beads seat.

http://home.comcast.net/~rwenzing/Backspacing_Alcoa_002_sm.jpg

http://home.comcast.net/~rwenzing/Backspacing_Alcoa_014_sm.jpg



This is a good cross reference for offset, width and BS:

http://home.comcast.net/~rwenzing/Width_Offset_BS_Chart.jpg

Thanks for the clearing things up.

Ok, so, after reading all this great information, I feel as though I get the concept, but can't apply it.

I am looking at getting new rims for my '01 Sport and can't figure out if I need the 4.5" or the 3.75" backspacing. I am going to get 15x8 rims and put 31x10.5x15 tires on them. I would rather not accidently destroy my bearings or something, so any help on this would be appreciated. Thanks!

3.75 for 15x8

and for 15x10 ??

is it 4 inches ?

Alloy wheels usually have the offset cast into the inside of the rim, example is 16x7x12, where 12 is the offset and using the chart shown in a previous post, that means 4.5" backspacing on a 7" rim. If you have deep backspace and want to move the tires AWAY from the truck, go for less backspace. Again use the chart, there is negative and positive offset listed.

I'm looking at a set of 17x9 wheels with 4.75 BS and -6mm offset. Could i run 33's with minor trimming? I've already got a 3in B/L, TT and shackles with 32x11.50x15 on the stock rims. I've read through this thread but it didn't really show different applications it only showed me how to calculate it. Preciate any answers.

-Justin

Hi guys. Kind of new'ish here but a long time Interweb and forum veteran elsewhere. One of those places is LegacyGT.com as I also have an '06 LGT Spec.B. I bring this up in the wheel/tire area here because I'm shopping new 18's and Nitto Terra Grappler 255/55/18s.

Lots of great info here particurlarly in this thread but it's not specific to our trucks. If any of you have the kind of experience, perhaps you work at a tire shop ;), that is detailed for my other car here: http://legacygt.com/forums/showthread.php?t=4426, it would be fantastic if you could graciously share with me and everyone else on here.

Another one of my favorites there, which I think could be really useful to Exp wheel/tire shoppers is this one http://legacygt.com/forums/showthread.php?t=19741, a compilation of pictures of installed shoes.

Yep. I've searched exhaustively and there is some information quite scattered about here and I'm still having trouble finding exactly what I'm looking for.

<flame on>

:D

ok. sorry, im confused. i am ordering 365/75 R16 mud tires or my 05 Sport Trac. i am trying to understand what all the backspacing and offset do. if i want my tires to stick a little bit out, what is a good backspacing and offset combo for a rim?

correction: ordering 265/75 R16 mud tires. sorry

Use the stock rims. Thats what i did when i had that size. If u want new rims, then get them with the stock offset (sorry dont know what that is). A good way to start is to pick the exact rims u want, then they usually only come in 1 or 2 offsets so it minimizes the possibilities. Remember, "offset" is the exact same thing as "backspacing" just a diff way of calculating it. Some rim cos use offset, some bckspc, some give u both numbers.

Sorry, I just saw you said you wanted them to stick out more.

I have 15" x 8" rims for my 33" tall 12.5" wide tires. The rims have a -19mm (-0.75") offset or a 3.75" backspacing. This offset is more negative than stock, which means they stick out a little more. The rim is also wider too (I believe stock width is 7"), so the rims stick out another 0.5" because of that.

With those tires (= 31.5" tall x 10.5" wide), I would run a stock 7" rim width (in either 15" or 16", any larger rim, you would need to go wider), but if you want to stick out more, go with a -19mm (-0.75") offset (this would equal a 3.25" backspacing on a 7" rim), which is slightly more negative than stock. It's best to be conservative when deviating from the stock numbers because a lot of things can change.

Did I confuse you yet?

ok. thanks. i think i am going to either a wider tire, or just get the next bigger size, the 285/75 R16

ok. thanks. i think i am going to either a wider tire, or just get the next bigger size, the 285/75 R16
does anyone know if 285/75 R16 mud tires will fit on stock Sport Trac rims? (16x7)

www.1010round rollie things/round rollie thingSizeCalculator.asp (http://www.1010tires.com/TireSizeCalculator.asp)

The text book says rim width range for that round rollie thing is 7.5" - 9.0".

Can you cram it onto a 7? Maybe, couldn't tell you.

uh ... looks like the forum is being hacked hardcore right now. what is going on??

uh ... looks like the forum is being hacked hardcore right now. what is going on??
yea, i think it being hacked or something. but yea, i saw that the rim width for the 285/75 R16 is 7.5 to 9 inches. i just didnt know if anybody had put that size on the stock rim. (16x7)

It's not being hacked..it's for april fools

oh. april fools. maybe it will be straight tomorrow.

I'm debating buying rims and i need to know if a 15x8 rim with 3.58'' backspacing will be ok. The offset is -30mm.

-Thanks

...If you click the "How To" in my signature, you will probably find your answer in the first paragraph..;)

I have read it and I know that the preferred backspacing is 3.75'' but i was just wondering if it would still work because of it being less. I still don't completely undertand it even though I've read it...obviously :dunno:

...Take a look at the last picture in the first post of this thread...;)

..The only difference is, you will have 3.58 BS (as you stated), and that is less than a 1/4 " different than 3.75" BS...This will push your wheels out just a little, I hope this helps...

...If I'm missing something, let me know...

I have an 07 X with stock 17 inch rims. I have no idea what the offset is. I want to put on 24x10" rims but I DO NOT want them to stick out. I also do not want them to rub on the inside as well. Can someone please help me out??

What exactly is the rubbing differences you guys have discovered between 15x8 with 3.75 and 4.00? (33's) Seems like I can find cheaper wheels that come in the 4.00BS than the 3.75BS..

From what I figure, 3.75 should put you at about stock with 15x8 and with 4.00bs on 15x8 they should stick out a little bit more? (considering the stock is 4.5?)

JCUZ, do you have any pics on how you made your eX an 8-seater???? I am making a "back" third row seat for the kids that they can fold down the factory back quarter seat to get in/out but if you have pics it'd make my life easier.

Ok, i am still confused. The rims I want run a 40 MM offset for the explorer bolt pattern, and if the 2001 Explorer Sport has a 0 offset, then what adapters do I have to use?

OK here is wait I am wanting to know I have a 1990 Ranger 2 wheel drive and I want to know can I mjake my rims from a 1992 F150 fit the Ranger. Now the Ranger has 14" on it and the F150 has 15"

you can just buy some 15" rims that match the lug nut size/distance OR I believe the website is spidertrax.com that sells wheel spacers & adapters. - ATTENTION - these are not cheap autozone/pep-boy stuff; they're designed and used for baja and serious riding!