Wheel offset explained: what +35, ET45 and -12 actually mean

Here is a thing that happens a lot. Someone finds the perfect set of wheels. The design is right, the finish is right, the price is almost right. They check the bolt pattern, it matches, they hit buy. Two weeks later the wheels are on the car and something is very wrong: either the tires are rubbing the suspension every time the steering turns, or the wheels stick out past the fenders like the car is trying to do the splits.

That something is almost always offset. It's a single number stamped on the back of every wheel, and it decides where the wheel sits in the fender: tucked in, perfectly flush, or poking out into traffic. It's also the spec people understand least. So let's fix that.

What offset actually is

Every wheel has a flat surface where it bolts to the car's hub. That's the mounting face. Every wheel also has an imaginary line running down the middle of its width: the centerline.

Offset is the distance, in millimeters, between those two things. That's it. That's the whole definition.

• Positive offset: the mounting face sits toward the outside (street side) of the centerline. Because the hub doesn't move, the wheel ends up pulled in toward the car.
• Zero offset: the mounting face is exactly on the centerline.
• Negative offset: the mounting face sits toward the inside (car side) of the centerline, so the wheel is pushed out. This is where the deep-dish look comes from.

On the wheel itself you'll usually see it written as ET followed by a number, like ET35 or ET-12. ET comes from the German Einpresstiefe, which roughly means "press-in depth". Some brands write "+35" or "35mm" instead. Same thing.

Why you can't talk about offset without width

Here's the quirk that trips people up. Offset is measured from the centerline, and the centerline depends on how wide the wheel is. So when you change width and offset at the same time, which is what most people do, the wheel moves in two directions at once.

Every extra inch of width adds half an inch (12.7 mm) on each side of the centerline. Then the offset change slides the whole thing in or out. Let's do a real example. Say your car came on 8.5-inch-wide wheels at +45, and you're looking at a 9.5-inch wheel at +35:

So the new wheel sits almost an inch further out at the lip, and barely moves on the inside. On a lot of cars that's the difference between a nice, flush stance and a tire that kisses the fender lip over every bump. On others, it's exactly what you wanted. The point is to know before you buy.

If you're comparing your stock wheel with a new one, the math is always the same: work out how far the outer and inner edges move, then check how much room you actually have on each side. Most wheel retailers have a free offset calculator that does this for you, and it's worth the thirty seconds.

Backspacing: the truck guy's version of offset

In the off-road world you'll hear backspacing more than offset. It's the distance, in inches, from the mounting face to the wheel's inner edge. It describes the same thing from a different angle: how much room the wheel takes up on the suspension side.

One catch: a wheel sold as "9 inches wide" is measured where the tire seats, and the lips add roughly another inch overall. So backspacing works out to about half of (width + 1 inch), plus the offset converted to inches. A 9-inch wheel at 0 offset has around 5 inches of backspacing; the same wheel at −12 mm has about 4.5 inches. Less backspacing, more poke.

What's typical, roughly

Every car is different, so treat these as ballparks, not specs:

• Most modern front- and all-wheel-drive cars come from the factory with fairly high positive offsets, often somewhere in the +35 to +55 mm range. That tucks the wheel in, which helps steering feel and packaging.
• Rear-drive sports cars and muscle cars are all over the map and often run different widths and offsets front and rear (a "staggered" setup).
• Trucks and off-road wheels often go to zero or negative offset, like 0, −12, −18, −24 or even −44 mm, for a wider stance and that pushed-out look. Bigger tires usually come along for the ride.

The right number for your car depends on its year, trim, brakes and suspension, and whether it's been lowered or lifted. Your owner's manual won't list offset, but the back of your current wheels will, and so will any good wheel seller if you give them your exact car.

What happens when you get it wrong

Too much positive offset (wheel too far in) and the inside of the wheel or tire can hit the suspension, the strut or the brake caliper. Big brake kits are especially fussy here, because the spokes have to clear the caliper as well.

Too little offset (wheel too far out) and the tire can rub the fender lip, especially when the suspension compresses or the wheel is turned. It also puts more leverage on the wheel bearings and changes the geometry the steering was designed around (engineers call it the scrub radius), which some people feel as heavier or twitchier steering. A little change is usually fine. A lot can be a problem, and in some places wheels that stick out past the bodywork aren't legal on the road.

What about wheel spacers?

A spacer sits between the hub and the wheel, so it moves the mounting face outward. In practice a 15 mm spacer does the same job as 15 mm less offset: +45 with a 15 mm spacer behaves like +30. Spacers are a legitimate tool for fine-tuning fitment, but quality matters. Use hub-centric spacers from a reputable brand, the right length of lug bolts or studs, and torque everything to spec.

A quick checklist before you buy

1. Note your current wheel's size, width and offset (it's cast or stamped on the back of the wheel).
2. Check the new wheel's bolt pattern and center bore. Offset doesn't matter if it won't bolt on.
3. Compare outer and inner movement with an offset calculator, like the table above.
4. If you have big brakes, ask the seller about caliper clearance for your exact car.
5. Decide on the look first, then the numbers. Which brings us to the fun part.

Get the look right first

Offset tells you where a wheel will sit. It can't tell you whether you'll actually like it on your car, and that's the part people regret most. Our advice: shortlist a few designs, see them on a photo of your actual car, then take that shortlist to a seller and sort out the numbers.

That's exactly what WheelTryOn is for. Upload a side or three-quarter photo and try any of our 386 wheels on it in about 15 seconds. It shows you the design and finish on your paint and your angle; it doesn't check fitment, which is why this guide exists.