Understanding Wheel ET.
The key to perfect fitment.
Wheel ET — or offset — determines where your wheel sits relative to the hub. Get it right and everything fits. Get it wrong and you get rubbing, poor handling, and suspension wear.
Introduction to Wheel ET
Understanding wheel ET is crucial for anyone interested in vehicle performance and aesthetics. Wheel ET, or offset, determines the distance between the wheel's mounting surface and its centreline. Get this measurement wrong and you risk tyre rubbing, poor handling, or clearance problems with brakes and suspension.
Whether you're selecting aftermarket wheels, fitting spacers to correct an offset, or simply trying to understand your car's specifications, knowing what ET means is the foundation of getting fitment right.
What is Wheel Offset?
Wheel offset is the distance between the wheel's hub mounting surface and its centreline, measured in millimetres. It determines how far in or out the wheel sits relative to the hub — and by extension, relative to the suspension, brakes, and wheel arch.
Offset affects the track width, which is the distance between wheels on the same axle. A more negative offset pushes wheels further out. A more positive offset tucks them in. This changes how the car handles, how the wheels look in the arches, and whether everything clears correctly.
Incorrect offset causes tyre rubbing against the arch or suspension components, uneven tyre wear, increased stress on wheel bearings, and in severe cases, contact with brake calipers. Spacers are the most common correction for offset that's too positive — they effectively reduce the offset and push the wheel outward to the desired position.
Wheel ET Explained
Wheel ET is short for Einpresstiefe — a German term meaning "insertion depth." It is the standardised measurement of wheel offset used across the automotive industry. ET and offset are the same thing expressed the same way: a positive or negative number in millimetres.
A higher ET value means the wheel's mounting surface is closer to the outer face. The wheel sits further into the arch. A lower ET value moves the mounting surface toward the inner edge, pushing the wheel outward. A negative ET pushes the wheel beyond the centreline toward the outside of the vehicle.
Positive → mounting surface outboard of centre
Negative → mounting surface inboard of centre
Example: a wheel marked ET35 has its mounting surface 35mm toward the outer face from the centreline.
ET is usually stamped or engraved on the wheel alongside the width and diameter — for example, 8J×18 ET35 means an 8-inch-wide, 18-inch-diameter wheel with an offset of 35mm. If you cannot find it on the wheel, it will be in your vehicle's manual or listed against your model in a fitment database.
| High ET (e.g. ET45+) | Wheel tucked in, more clearance from arch, common on front-wheel-drive cars |
| Low ET (e.g. ET25) | Wheel pushed out, wider stance, more common on performance and rear-wheel-drive cars |
| Negative ET | Wheel sits beyond hub centreline, typical on off-road and wide-arch builds |
| Zero ET | Mounting surface perfectly centred, uncommon on modern vehicles |
Understanding the Three Types of Offset
Offset is categorised as positive, negative, or zero. Each behaves differently in terms of wheel position, clearance, and handling.
The mounting surface is closer to the outer face of the wheel. The wheel sits further inside the arch. Most modern vehicles — particularly front-wheel-drive cars — use positive offset, typically between ET35 and ET55.
The mounting surface is closer to the inner edge. The wheel is pushed outward beyond the centreline. Common on off-road vehicles, wide-body builds, and deep-dish wheels.
The mounting surface sits exactly at the centreline. Neither inboard nor outboard. Uncommon on modern vehicles but found on older and specialist applications. Maintains a perfectly even weight distribution across the wheel face.
ET35 vs ET40 — What's the Difference?
ET35 and ET40 are two of the most common offset values on performance and aftermarket wheels. The 5mm difference is small but meaningful, particularly on low-profile setups or lowered cars where clearance margins are tight.
The wheel sits 5mm further outward compared to ET40. This widens the track slightly, which can improve cornering feel and gives a more aggressive stance in the arch.
The wheel sits 5mm closer to the hub centreline. More clearance from the arch lip, fewer rubbing concerns. The more conservative choice for daily-driven cars or those that haven't been lowered.
If your wheels are ET40 but you want the stance of ET35, a 5mm spacer achieves exactly that — without changing wheels. Brightstone Engineering machines hubcentric spacers in a range of thicknesses to let you dial in offset precisely. Extended bolts are included in every kit.
Wheel Dimensions and How They Relate to ET
ET does not exist in isolation. It works alongside the wheel's width and diameter to determine whether the wheel fits correctly within the arch and clears the suspension and brakes.
As wheel width increases, the offset must be adjusted to avoid pushing the wheel into the arch or suspension components. A wider wheel extends both inward and outward from the mounting surface — so even if the ET stays the same, a wider wheel will sit further out than a narrower one.
| Diameter | Affects tyre size, ride quality, and brake clearance. Larger diameters reduce sidewall height and can stiffen ride quality. |
| Width | Wider wheels extend both inboard and outboard. Offset must be adjusted when width changes to maintain correct positioning. |
| Offset (ET) | Controls the lateral position of the wheel. Must be recalculated whenever width or diameter changes significantly. |
Increasing diameter alone — for example moving from 18" to 19" — usually requires a small offset adjustment to maintain proper alignment. The key is ensuring the tyre stays within the arch at full suspension compression and lock-to-lock steering movement.
Common Wheel Specifications
Beyond ET, every wheel has three specifications that must match your vehicle:
- Bolt pattern (PCD) — the number and arrangement of lug holes. Must match the hub exactly.
- Centre bore — the large central hole that locates the wheel on the hub. A mismatch causes vibration.
- Load rating — the maximum weight the wheel can carry. Exceeding this is a safety risk.
These three, combined with ET, define whether a wheel fits your car safely and correctly. Getting all four right is what fitment means in practice.
How to Find Out Your Wheel Offset
There are three reliable ways to identify your wheel offset:
- Check the wheel itself — ET is usually stamped or engraved on the inside of the wheel barrel, alongside the width and diameter. Look for a marking like 7.5J ET38.
- Consult the vehicle manual — OEM offset is always documented. This gives you the factory spec to work from when selecting aftermarket wheels or calculating spacer thickness.
- Use a fitment database — most wheel retailers and fitment tools list ET ranges for every make, model, and year.
When fitting aftermarket wheels with a different ET to OEM, always check clearance at full steering lock and at full suspension compression before committing to the fitment. If the wheels are too far in or out, a spacer can correct the position without changing the wheel.
Practical Implications of Wheel Offset
Choosing the right offset has a direct impact on safety, tyre life, and how the car looks and handles.
Benefits of correct offset
- Improved handling and stability — wheel geometry stays within design parameters
- Optimal tyre wear — even contact patch across the tread
- Correct brake clearance — no contact between wheel spokes and callipers
- Flush or desired arch fill without rubbing
Problems caused by incorrect offset
- Tyre rubbing against the wheel arch at full lock or over bumps
- Wheel spokes contacting brake calipers
- Increased stress on wheel bearings from changed scrub radius
- Uneven tyre wear from altered geometry
- Poor handling and steering feel
Common mistakes to avoid
- Misjudging offset — even 5–10mm can cause rubbing on a lowered car. Always check against your specific setup.
- Ignoring wheel width changes — a wider wheel at the same ET sits further out than a narrower one.
- Mismatching tyres and wheels — running a tyre outside the approved width range for a given wheel width affects handling and wear.
How to Choose the Right Wheel for Your Vehicle
Selecting a wheel comes down to three questions in order:
- Does it match the vehicle specs? — PCD, centre bore, and load rating must all be correct before considering anything else.
- What is the purpose? — Daily driving, track use, and show builds all benefit from different offset choices. Daily driving favours OEM-adjacent ET. Track use often favours a slightly wider track. Show builds may go further.
- Does it clear everything? — Check at full lock and full suspension travel. If it doesn't clear, a different ET or a spacer is the answer.
Spacers give you more flexibility here than most people realise. If you find a wheel you like in the right PCD and bore but the ET is slightly too positive — meaning it sits too far into the arch — a spacer of the right thickness corrects the position exactly, with no compromise on the wheel itself.
The right spacer corrects offset precisely.
Find spacers matched to your car
Every Brightstone spacer is machined to match your PCD, centre bore, and hub. Extended bolts included. UK-made, hubcentric, lifetime warranty against defects.
