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Offset How-to

Tire Wheel Backspacing Offset Calculators

Wheel Offset and Backspacing

So you finally saved up the cash to get the perfect set of wheels for your ride, now what. There’s diameter, that’s the easy part, your favorite song says you need some 24s! Now you just google your vehicle to find out the number of lugs and distance between them, 6 lugs 5.5″ spacing 6×5.5. Okay all set, go on eBay and order some wheels… Not so Fast! Did you know many wheels are sold in 3-10 different wheel offsets or ET (some German abbreviation for offset). The wheel offset is the distance in millimeters (mm) that the hub of the wheel (where you bolt the wheel to the car) is from the True center of the wheel. Basically a positive offset of +25mm means the center of the wheel is 25mm closer to the outside (curb/fender side) of the wheel, thus pushing the wheel in toward the caliper/brake. This basically sinks the tire and wheel into the fender. If the same wheel were to have a wheel offset of -25mm, that means the center (lug nut or mounting part) is closer to the inside of the wheel. This is what often creates a larger lip on the wheel or a concave style wheel, Thus pushing the tire out toward the fender making it flush or on your favorite monster truck way outside the fender creating that super aggressive 4×4 stance.

How to Measure our Backspacing (Back of the wheel)

Measuring Backspacing

Or hopefully you can just look on the back side of the wheel/rim and find this stamping!

PENTAX Image

(This would be a 18″ diameter with 8″ width and +55 offset.)

 

Let me start by just throwing all the math at you, then you will see some diagrams and explanation below.

Using 205/60-15 as an example:

Tire width = 205 mm

Aspect Ratio = 60 (sidewall height is 60% of tire width) or 0.6 * 205 = 123 mm side wall

Wheel rim dia. = 15 inches

So the INCHES diameter of a 205/60-15 tire is = (2*205*0.6/25.4) + 15 = 24.69 inches diameter is same as “height”

 

formula from mm and ratio to inches:

((2*tire width mm*tire ratio*)/25.4)+rim diameter inches = tire height in inches

For width tire width mm/25.4 = width inches

 

To convert from inches to mm

Tire width = 8″

Tire height = 25″

wheel dia. 15″

formula

(tire width in * 25.4) = width mm then round to 5mm or 8*25.4 = 203.2 or 205mm

((Tire height – rim diameter) / 2) / (tire width in * 25.4)

 

formula from inches to ratio in %

((Tire height inches- rim diameter inches) / 2) / (tire width inches)= % again round to nearest 5 (60 or 65 using our previous numbers)

For width tire width inches * 25.4 = width mm

top view wheel offset w logo

As the offset is moved toward the Curb Side (positive + offset) – toward the fender – it has the opposite effect on the wheel stance, moving it in toward the caliper which creates a larger gap between the outter edge of the tire and the outer edge of the fender. As the offset moves toward the caliper (negative – offset) the wheel and tire are moved out toward the fender and with a large enough negative offset the tire will stick out past the fender.

CAUTION – CAUTION – CAUTION

The following diagrams assume the wheel is the same width in both examples. Remember if the wheel width changes this will affect how much the offset will move the wheel. Example: a 7.5″ wide wheel with a +25 offset will be “tucked” into the fender while a 10″ wide wheel with +25 wheel offset could be flush. How? You have to account for the 2.5″ of extra wheel width. That mean 1.25″ on each half of the wheel from the center line. Since every inch is worth 25.4 mm that means you have added 31.75mm of wheel toward the fender and another 31.75mm toward the caliper, even though the offset was the same.

BACK to CLASS NOW

Assuming you are keeping the same width wheel, this is what offset would do as you change from positive offset such as +25 to less positive such as +12 or past the center line of the wheel to negative wheel offset such as -12.

First an example looking from the rear of a vehicle with a stock or positive offset. The suckin or tucked, factory look.

rear view positive wheel offset w logo

This second diagram looking from the rear of a vehicle with a negative offset (same width wheel). This setup will give the flush or with a larger negative offset one can achieve the aggressive look as you move outside the fender.

rear view negative wheel offset w logo

BACKSPACING

So now that you know exactly what wheel offset is we will move on to the other word used by the custom wheel world. Backspacing. Not all that different however to keep you on your toes it changes where we measure from. We are still looking for the distance from the mounting surface of the wheel, however rather than measuring to the ‘center line’ of the wheel, backspacing is measured from the back edge of the wheel to the mounting surface. Like below.

What is Offset?
by: Custom Offsets

Confusing? Not a big deal that’s why CustomOffsets.com exists. You don’t have to worry about all this because we have created a place to SEARCH. BROWSE. and SHARE pictures of your favorite rides with the specifications of the wheels, including wheel offset to make finding the perfect wheel for your ride sooooo much easier!

Tire Wheel Backspacing Offset Calculators

FOR FITMENT ASSISTANCE AND KILLER PRICES ON OUR SETUPS SIMPLY EMAIL SALES@CUSTOMOFFSETS.COM.


Home Offset How-to
  1. hi i have 17 inch rims 7.5 offset 44 6 lug nuts i added fender flares on my truck and they kind of big . thats what i get for paying cheap on the net anyway i want bigger size rims what offset wud i need to get my tires flush or close to my fender flares

  2. In your formula for calculating backspacing ((Actual wheel width + 1)/2) + (offset mm/25.4) where does the “+1” come from? Why are you adding an inch to the actual wheel width prior to dividing in 1/2?

    • That would be because the actual size of a 10″ wide wheel is truly 11″ wide from edge to edge. Also with 9″ actually being 10″ and so on….

  3. I have a 2015 escalade esv, my stock offset is +25
    I want to put a 305/35/24 on a 24×10 rim. Should I go with +20 or +30? that’s the only sizes the rim comes In.

  4. Hi all
    I’ve got 8Jx15 Et-25 wheels with 30×9.5 R15 tires on YJ Wrangler, and my rear bearing gone dead. New bearing… gone… DEAD! In just 100 kilometers! Mechanic at the shop says that “oversized wheels” caused bearing failture. Could it be so?

    • That setup is honestly not that drastic compared to stock. I would be more concerned as to the quality of the bearings. We see Jeeps with wayyyyyy more aggressive setups with zero issues. I would get you some lifetime warranty bearings because they shouldn’t be failing that soon!

  5. 255/60-15 on my nova. tire very close to fender 3/8 in. like to offset and get more clearance. about 1 in. from shock. how much offset do you think i can go? Thanks Randy

  6. I want to but 24” rims on my 99 Silverado 1500 I want the widest rim I can tuck, I do not mine cutting bed what would be the measurement that would best fit?

  7. Hi I am looking at going from the stock 7.5 x 17 wheel with 285/70R17 on my 2008 gmc to 9 x 17 with 285/70R17. Right now my inner wheel rubs slightly when pinned either direction. I am afraid if I go with the plus 1 offset the outside of the tire will rub on the inner fender. Should I go with +20 offset instead. I also don’t want the tirwes to stick out much more.

  8. How bad is it to run 15×10 with 2″ wheel spacers on a 2008 ford ranger?

  9. Looking to buy new rims. Can’t decide between 10 wide and 12 wide. Can anyone tell me how much more a 12 wide will hang out? Assuming the 10 wide has a -24 offset and 12 wide has a -44 offset.

  10. you do a good job of explaining wheel offsets until you get to backspacing. Your result appears to have a math error. You state the backspacing in the example is 6.48 but the correct result according to your formula is 6.88.
    let me know if you agree.

  11. My tires on my truck are 35 x12.50 xr 20 and I want some lip on my rims but I don’t want any tire hanging out under the fenders I want them flush with the edge of the fenders and honestly I know nothing about +or – offsets so what side rim do I need for no tire hanging out the edge

  12. getting ready to put on 33″ tires but wondering if I need to change the wheel bearings also.

  13. Hello am looking for 26×14 for a 2017 f150 i have 8 inch lift with 24×12 tire size is 375/40r24 would i have a nuff room for 26×14 with 37×13.50r26

  14. will rims with a -25 fit on stock tires 275 60 r20? I need new tires on my ram but can’t afford rims right now but I like the look of the rim that sticks out about an inch or so from the fenders

  15. Looking to run 24×12 fuel cleavers on my 16 Sierra 2500 crew cab l/b. Looking at fuel gripper m/t tire please tell me the lift I need and what else I need and do u carry this setup need ASAP thanks

  16. I’m in Germany and they have laws that prohibit you from running tires that stick out past the fenders. My truck, 13 F150 FX4 with a 6″ lift and normally run 37×12.50’s. Needing to change my set up, what offset could one run with 4″ fender flares, while keeping the wheels/tires under the flare? If I’m correct, the stock 20’s I’m running have a +38 offset, and MAN DOES IT LOOK UNSIGHTLY!! Haha!!

    Thanks for your time
    Justin

  17. Hello, what is ment by the term stance???,and can you explain flush,super,aggressive etc. Thanks😊

    • When the term “Stance” is used on a lifted truck its referring to the tires and wheels sticking out past the fender. Flush is flush with the fender. So as you go out further past the fender it goes slightly aggressive, aggressive >1″, super aggressive 3″-5″ and hella stance >5″ Those measurements are from the fender out and terms we came up with. Hope that helps explain it a little better!

  18. I am trying to go with 17×8 +30 all around on my 97 honda prelude.. I have the f&f type 1 suspension and I am looking for good look for the car (flush)
    Will I have any issue with that?
    I am trying to run 205/40/17.

  19. I did fill thequote sheet

  20. i am lost. I have a 2016 f150, 4X4 and I have a 2″ level in the front and 305/55/20 tires.I want new wheels to stick just half an inch out of the fenders. what size should I be looking for? please help

  21. Thanks for such helpful explanation. By how much can offset be changed safely and still have a notable difference?

  22. I’ve already submitted a quote sheet. Just wanted to say thank you for explaining VEHICLE offset and backspace. Everyone else wants to explain about the wheels either stock or aftermarket, but won’t or can’t explain the real life differences available for the car or truck itself.

  23. I have an 08 Ford Edge Limited AWD. I want to run 24″ rims. Are you able to help me with fitment?
    Bolt pattern – 5X114.3
    Offset – +35

  24. I have a 2002 f250 10 lift what offset do I need for 15.5 43.5 tall

  25. Im sorry I meant 6″ backspace

  26. I would like a cragar SS type wheel for a 65 Catalina 7″ wide with a 6″ offset 5 on 5 is this possible

  27. I’m looking to run 18×10 wheels on my lowered c10 chevy. 1987. We would like the deepest dish possible on the rear. I found some American racing torque thrust II that are 18×10 with a 5.75 backspacing.
    And fronts that are 18×9 with a 5″ backspacing. We are hoping the rest will tuck and have a decent lip on the rear. Any suggestions?

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