Stupid question, but could somebody explain wheel offset to me?

"Big Bubba Ray" (eganward01) 06/17/2014 at 23:21 • Filed to: None

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I can't get a clear, concise answer anywhere online. A guy in my area is selling the wheels from his 2013 WRX and I was thinking of slapping them on my 05 Outback if they will fit. The 2013 WRX wheels are 17x8 with a +55 offset and I'm pretty sure my Outback's current wheels are 16x6.5 with either a +44 or +55 offset. Da fuq is offset?

I'm a hella wheel n00b. If these wheels would fit on my car, I'm most likely going to buy them and use my current wheel set for winter tires.

Have a wagon for your time.

nFamousCJ - Keeper of Stringbean, Gengars and a Deezul > Big Bubba Ray 06/17/2014 at 23:26

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by the looks of it the more the offset the close the mounting surface to the actual wheel hub. 0 offset is centered and negative offset the wheel is overlapping the hub? Maybe? Pretty wagon though

beardsbynelly - Rikerbeard > Big Bubba Ray 06/17/2014 at 23:26

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It's how far away the hub mounting surface is away from the center line of the wheel. The larger the number the further away it is. Nearly all OEM wheels are positive offset. +44 is closer to the center line than a +55

Zipppy, Mazdurp builder, Probeski owner and former ricerboy > Big Bubba Ray 06/17/2014 at 23:26

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Think of it like this:

Positive sticks out, negative goes the opposite. If the offset is the same, then the wheels will sit the same as your current ones are. check the included diagram.

theloudmouth > Big Bubba Ray 06/17/2014 at 23:27

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Picture is worth a thousand words in this case.

XJDano > Big Bubba Ray 06/17/2014 at 23:27

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Distance from center of wheel?

Thus some are positive some are negative.

On the jeep and offroading they use backspacing. Distance from inside of wheel to mounting surface. Stock XJ is 5.5" aftermarket is usually around 4" so they stick out more.

Here is a picture of a wheel since everyone else is posting the same diagram.

E30Joe drives a Subaru > Big Bubba Ray 06/17/2014 at 23:28

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The face where the wheel meets the hub is where it is measure from. +55 means that if you cut the wheel perfectly in half it would be 55 mm from the center line. 0 offset would be in the middle of the wheel, anything negative would be the opposite. And the WRX wheels will fit.

DasWauto > Big Bubba Ray 06/17/2014 at 23:30

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This image should explain it pretty well.

If your wheels are the same offset as those WRX wheels (+55) the new wheels will be 3/4" closer to the centre of the car and will stick out 3/4" more (due to the width of the wheels, not to do with the offset).

Sometimes if you are changing wheel sizes (widthwise) you have to go with a different offset to prevent rubbing on the car.

They're the same bolt pattern I assume (5x100, right), so I would just jack up the front of the car and try them.

Big Bubba Ray > E30Joe drives a Subaru 06/17/2014 at 23:31

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Thanks for the explanation! I was hoping you would chime in.

Big Bubba Ray > DasWauto 06/17/2014 at 23:31

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Yep, same bolt pattern. 5X100. Thanks for the pic!

E30Joe drives a Subaru > Big Bubba Ray 06/17/2014 at 23:33

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;) I'm a wheel whore.

PheeNoIVI > Big Bubba Ray 06/17/2014 at 23:34

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Dude thank you for asking! Ive been wanting a clear answer as well

Big Bubba Ray > PheeNoIVI 06/17/2014 at 23:37

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Haha I have no shame in asking Oppo questions! I'm constantly asking stupid things and everyone is always willing to help.

PheeNoIVI > Big Bubba Ray 06/17/2014 at 23:40

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Lol yeah we have some great people here. I got new rims and tires a few weeks ago. And I got told nice wheels love the offset. I was like uhh.. Thanks lol

ttyymmnn > theloudmouth 06/17/2014 at 23:50

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Picture is worth a thousand words in this case.

Aaaannnndd.....Nibbles ate your picture.

BoxerFanatic, troublesome iconoclast. > Big Bubba Ray 06/18/2014 at 00:12

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Legacys and other lower Subarus have 55mm positive offset, as the images show, the mounting surface of the hub is way out toward the outside of the wheel, (can otherwise be thought of as pushing most of the wheel's tire width inboard in relation to that hub mounting surface)

Outbacks have fender flares, and ride taller, so the suspension droops more. As the suspension droops and the angle of the lower control arm changes, the effective track width of the car, measured from the bottom centerline of one tire's contact patch to the center of the tire on the other end of the same 'axle' shortens on an independent suspension car, since the suspension moves in an arc motion on each side.

In order for the wheels not to look ridiculously tucked away under the fender flares, the Outbacks, Foresters, and some other taller-height Subarus use wheel offsets that are a little less drastically positive, closer to 45-48mm positive offset.

+55mm offset wheels from a Legacy or WRX will directly fit an Outback, but unless they are 15-20 millimeters wider, they will tuck further under the fenders. An 8" wide aftermarket wheel is ~25.4mm wider than a stock 7" wide wheel. If a positive offset increases by half that distance, the wheel stays in the same relative position, with half the additional wheel width inward, and half outward. A zero offset wheel would stay at zero, and a negative offset wheel would have to go more negative to keep the same relative position at the hub surface.

The wheel diameter is inconsequential to offset, but width does matter. Going from a 6.5 inch wide wheel, to an 8 inch wide wheel converts to 38.1mm A 38 millimeter difference in width, but only a 10mm increase in offset, which is less than half, and actually barely more than a quarter of the additional total width.

That means the new wheels, with the fixed position a the wheel hubs, the inner side of the tire will move inward by 29 millimeters (half of 38 is 19mm, plus the 10mm additional offset), and the outer side of the tire will move outward by 9mm. (19mm minus that additional positive offset)

Since they are stock Subaru wheels, and Subaru suspension is largely the same, (2009-14 Impreza/WRX/STI chassis was derived from the 2005-2009 Legacy/Outback chassis), the wheels should fit without contacting the struts on the inside, and hopefully should not have a problem rubbing on the internal fender liners. Since factory Subarus, like most other cars, are conservative with their wheel fitments, and don't usually push them outward toward "flush" with the fender edges, plus Outback's additional flare width and ride height compared to Legacy, 9mm outward extension will likely still fit. 2011-14 WRXs with lowered ride height did have the same flared fenders as WRX STI, which allowed the wider wheels on a lower riding car, with the factory large clearances.

If your outback is lowered like the one pictured, then it basically becomes a Legacy wagon, the lower control arm length gets horizontal, rather than drooping diagonally, and the track width between the hubs is at it's maximum where the lower control arms are horizontal. At that point, it may require Legacy's additional few millimeters of positive offset on the wheels, to keep them inside the fender wells, rather than sticking out.

I had 18x8 +55mm offset Rota Torques on my previous '05 Legacy GT, and they did fit, without rubbing, even with slightly lower springs and Bilstein Spec.B struts, so I don't think it will be a problem on your Outback. Chances are, it will look much more substantial.

However... keep up with your suspension maintenance. Increasing wheel weight and leverage with larger, wider wheels and tires, will wear on wheel bearings, and suspension bushings faster. Keeping up with bushing lubrication, and replacing shocks and wheel bearings when they start to complain will keep it in good shape, but letting them go will cause headaches.

Hopefully that is about as clear as mud for you.

beardsbynelly - Rikerbeard > XJDano 06/18/2014 at 00:17

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that dog is about +175 offset

Big Bubba Ray > BoxerFanatic, troublesome iconoclast. 06/18/2014 at 02:36

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Dang, I'm glad there are Subaru aficionados around here haha

Thanks for the help! I'm gonna call the guy tomorrow to see if they're still available. If so, I'll test fit them on the front to make sure they don't rub at all. If it all checks out, I'll snag them. Thanks again!

Shiarlis > Big Bubba Ray 06/18/2014 at 02:48

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You're a hella wheel noob, these are Hella horns. Perhaps they can help?

AMGtech - now with more recalls! > Big Bubba Ray 06/18/2014 at 05:05

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Changing wheel sizes and offset will also alter your scrub radius, not to mention other things. Which will in turn affect handling and tire wear. Without going into a couple hundred pages worth of suspension/steering theory, I suggest having your car aligned by someone competent and also pay attention to your tire wear. But on the other hand, nobody else pays any attention to all of that. Oh well, at least now you know, sort of. It's late (or early?) And I need to try to catch a few hours of sleep.

You can tell a Finn but you can't tell him much > beardsbynelly - Rikerbeard 06/18/2014 at 16:59

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My wheels are size 17x8JJ. Do you have any idea what the JJ means? I've never been able to figure it out or find that information online.

beardsbynelly - Rikerbeard > You can tell a Finn but you can't tell him much 06/18/2014 at 18:33

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it's an indicator of the size of the flange on the outside rim that the bead of the tire sits on.

Essentially the part of the rim that the tire presses against lateraly that stops it from falling off the rim.

You can tell a Finn but you can't tell him much > beardsbynelly - Rikerbeard 06/18/2014 at 23:09

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Thanks, it has always bugged me that I could never find out what that meant.

beardsbynelly - Rikerbeard > You can tell a Finn but you can't tell him much 06/19/2014 at 00:57

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no problem, don't ask me how they came up with the letters though. That's anyone's guess.