What is ET on rims and why is it important for your vehicle?
If you've ever bought wheels or been interested in tuning a car, you've probably come across the mysterious abbreviation ET. This is not a mistake or a marketing ploy - it's disc offset, a critical parameter that determines how the wheel will “sit” on the hub. Difference between ET35 and ET45 may seem insignificant at first glance, but in practice it affects handling, suspension wear and even safety.
The offset is measured in millimeters and shows the distance from the mating plane of the disk (the one that presses against the hub) to the imaginary center line of the wheel. If ET positive (for example, ET45), the disk is “recessed” inside the arch. If negative (ET-10), the wheel sticks out, giving the car an aggressive look. But why is it so important to follow the manufacturer's recommendations? Because the wrong offset displaces load vector on the suspension, accelerating the wear of silent blocks, wheel bearings and even the steering.
In this article we will look at the specific differences between ET35 and ET45, how does this affect the behavior of the car, and is it possible to install wheels with a different offset if you “really want to”. Spoiler: sometimes you can, but with reservations. You will also learn how to calculate permissible deviations and what to do if you bought disks with the wrong ET.
ET35 and ET45: what do these numbers mean in practice
Let's break it down into pieces. Numbers 35 and 45 in ET markings these are millimeters. But millimeters of what?
- 📏 ET35: disc offset is 35 mm from the central axis of the wheel. This means that the mating plane is offset inside 35 mm relative to the center. Such wheels visually make the track wider and the car more stable when cornering.
- 📏 ET45: departure is already here 45 mm, that is, the disk is “recessed” deeper into the arch. At the same time, the wheels look less convex, and the load on the wheel bearings is distributed differently.
For example, if your car comes from the factory with wheels with ET45, and you decided to put ET35, the wheel will move outward by 10 mm on each side. This will increase the track by 20 mm (10 mm on the left and right), which can lead to:
- ⚠️ Wheel friction against the fender liner or arch when fully loaded or on uneven surfaces.
- ⚠️ Accelerated wear of wheel bearings due to a modified load lever.
- ⚠️ Unpredictable behavior at high speeds (especially relevant for rear-wheel drive and all-wheel drive cars).
But not everything is so simple. On some vehicles, e.g. Volkswagen Golf or Skoda Octavia, the difference between ET35 and ET45 can be acceptable if the wheel and tire widths are chosen correctly. It all depends on amount of space in the wheel arch and suspension designs.
How offset affects handling and safety
Changing the reach isn't just about aesthetics. This engineering parameter, which is directly related to the physics of vehicle motion. Let's figure out how ET35 and ET45 affect key characteristics:
| Parameter | ET35 (lower offset) | ET45 (longer reach) |
|---|---|---|
| Cornering stability | ↑ Higher due to wider track | ↓ Below, rolls are possible |
| Suspension load | ↑ Increased by levers and silent blocks | ↓ Distributed closer to the hub |
| Wheel bearing wear | ↑ Accelerated (20-30% faster) | ↓ Within normal limits |
| Visual effect | Wheels “stick out”, aggressive look | Recessed wheels, classic look |
| Arch compatibility | ⚠️ Risk of friction with large suspension travel | ✅ Usually no problem |
It is especially critical to maintain the offset on vehicles with independent multi-link suspension (for example, Audi A4 or BMW 3-series). Here, a displacement of even 5-10 mm can lead to uneven tire wear and loss of directional stability at speeds above 120 km/h.
⚠️ Attention: On four-wheel drive vehicles (eg Subaru Forester or Mitsubishi Outlander) a change in offset by more than ±5 mm from the factory one can lead to damage to drive shafts due to a change in the angle of operation of the CV joints.
What about comfort? Wheels with a shorter offset (ET35) make the suspension stiffer - you will “feel” road irregularities more often. ET45, on the contrary, retains the factory softness, but may worsen the “sharpness” of the steering.
Before purchasing wheels with a non-standard offset, check whether the wheel arch has space reserve for offset. To do this, take a ruler and measure the distance from the inside of the tire to the fender liner with the wheels fully turned out.
Is it possible to install ET35 instead of ET45 and vice versa?
Short answer: possible, but not always. The long answer requires an analysis of three factors:
- Manufacturer's factory tolerances (specified in the instruction manual).
- Suspension type (McPherson strut, multi-link, torsion beam).
- Wheel width and tire profile (wide wheels + low profile = less arch clearance).
For example, on Toyota Corolla (ET45 from the factory) you can install wheels with ET38-ET42 without consequences if the disk width does not exceed 7J. But on Ford Focus ST with its sensitive suspension even ET40 instead of ET50 may cause vibrations in the steering wheel.
General rule:
- ✅ Deviation is acceptable ±5 mm from factory ET for most passenger cars.
- ⚠️ Deviation 5-10 mm requires checking for compatibility (possible abrasions or accelerated wear).
- ❌ Deviation more than 10 mm — risk of suspension failure or loss of control.
If you still decide to experiment, use spacers (adapters for departure). They allow you to compensate for the difference, but remember: spacers must be certified and installed in pairs (on both sides of the axis).
What happens if you install wheels with ET20 instead of ET45?
With such a radical change in offset (25 mm on each side), the wheels will move outward by 50 mm in total. This will result in:
- ⚠️ Friction of the tire on the fender liner even on small bumps.
- ⚠️ Risk of wheel “flying out” during a sharp maneuver (the leverage of force increases).
- ⚠️ Wheel bearing failure within 10-15 thousand km.
On some vehicles (for example, Nissan Juke or Renault Captur) this can also affect the brake calipers.
How to measure disc offset yourself
If you bought used wheels without markings or are in doubt about the specified parameters, you can measure the offset yourself. You will need:
- 📏 Ruler or caliper (more precisely).
- 🪛 Square (or any object with a right angle).
- 📝 Paper and pen for notes.
Algorithm of actions:
- Place the disc on a flat surface face down (the one that presses against the hub).
- Attach the square to the rim and measure the distance from the surface to the mating plane (parameter A).
- Turn the disk over and measure the distance from the surface to inner edge of the rim (parameter B).
- Calculate the offset using the formula:
ET = (B - A)/2 - A.
Example: if A = 100 mm, and B = 200 mm, then ET = (200 - 100)/2 - 100 = 50 - 100 = -50 mm. This means that in front of you is a disk with negative offset (ET-50).
View factory settings in owner's manual|Measure wheel arch clearance (including suspension travel)|Check wheel width and tire profile compatibility|Ensure spacers (if required) are certified and fit|Consult suspension specialist if ET deviation is greater than 5mm-->
Examples of ET35 and ET45 compatibility on popular cars
To make it easier for you to navigate, we have collected data on several popular models. Please note: this general recommendations, not absolute truths. Always check the parameters for your modification!
| Car model | Factory ET | Allowable ET range | Notes |
|---|---|---|---|
| Volkswagen Golf 7 | ET45-ET50 | ET40-ET55 | ET35 is only possible with rims up to 7.5J wide |
| Toyota Camry XV70 | ET40 | ET35-ET45 | ET45 can touch the calipers on versions with larger brakes |
| Hyundai Tucson (TL) | ET42 | ET38-ET48 | ET35 requires testing for compatibility with all-wheel drive |
| Ford Kuga 2 | ET50 | ET45-ET55 | ET35 is not recommended due to the risk of suspension damage |
On crossovers (for example, Kia Sportage or Mazda CX-5) a common problem with hitting the fenders when installing disks with ET35. This is due to the fact that they short travel suspension, and even a slight outward movement of the wheel leads to friction on bumps.
⚠️ Attention: On vehicles with electronic assistance systems (ESP, ABS, traction control) changes in offset may cause false positives due to changes in wheel dynamics. For example, on Skoda Octavia 4 with ET35 instead of ET45 the ESP light may be constantly on.
Myths and misconceptions about disc wear
There are many myths floating around the ET topic that could cost you money or security. Let's look at the most common ones:
- 🚗 “ET is not important, the main thing is that the disc fits on the hub”
Reality: Yes, the disc can be physically bolted on, but shifting the center of mass of the wheel will change the load on the suspension. It's like putting on shoes one size too big - you can walk, but it's uncomfortable and harmful to your feet. - 🔧 “Spacers will solve all problems”
Reality: Spacers compensate for offset, but increases the load on the hub bolts. At speeds above 140 km/h this can lead to their deformation. - 💨 "Smaller ET improves handling"
Reality: Only if the car was originally designed for a wide track (for example, sports models). On civilian vehicles this often leads to oversteer and risk of skidding.
Another misconception: "ET does not affect fuel consumption". In fact, changing the offset changes moment of inertia of the wheel, which can increase consumption by 0.3-0.7 l/100 km. This is especially noticeable on cars with low-power engines (up to 120 hp).
If you are not sure about the choice of departure, always rely on factory parameters. Even a small deviation (5-10 mm) must be compensated by changing the width of the rim or tire profile.
FAQ: Frequently asked questions about ET35 and ET45
Is it possible to put wheels with ET35 on a car that came from the factory with ET45, if they are visually suitable?
Theoretically yes, but you need to consider:
- Wheel width: if it is larger than the factory one, the risk of friction with the fender liner increases.
- Drive type: on all-wheel drive cars (for example, Subaru Impreza) this can damage the CV joints.
- Driving style: If you drive aggressively, the suspension will wear out faster.
Best consult with a specialist or use 3D modeling (for example, in the program Wheel Fitment PCD).
Which offset is better for lowered suspension: ET35 or ET45?
On lowered cars (stance or lowriders) usually use disks with less overhang (ET35 or even ET20) to:
- Compensate for reduced ground clearance.
- Achieve a visual effect “flush” with the arch.
However this requires precise fit and often leads to:
- ⚠️ Friction of the tire against the fender liner during full suspension travel.
- ⚠️ Need to use stretched tires (stretched tires), which impairs grip.
Does offset affect the life of wheel bearings?
Yes, and very significantly. Reach increase (for example, moving from ET35 to ET45) reduces the load on the bearings, as the wheel moves closer to the center of the hub. And vice versa:
- Reducing the offset (ET45 → ET35) increases leverage, which is subject to force, which accelerates bearing wear in 2-3 times.
- On vehicles with heavy weight (crossovers, SUVs) the effect appears faster.
Average wheel bearing life with correct ET: 100-150 thousand km. If incorrect - 30-50 thousand km.
Can spacers be used to adjust offset?
Spacers are a temporary solution that has its own nuances:
- ✅ Pros: allow you to “adjust” ET to the desired parameters without purchasing new disks.
- ❌ Cons:
- Increases the load on the hub bolts (risk of failure at high speeds).
- May cause vibration if unbalanced.
- Not all spacers are certified for road use.
If you still decide to use them, choose spacers from aviation aluminum or steel, with centering rings.
How does offset affect the operation of ABS and ESP?
Electronic stabilization systems (ABS, ESP, TCS) are calibrated to factory suspension geometry. Changing the offset can:
- ⚠️ Call ABS false alarms on uneven surfaces (the system perceives changes in wheel dynamics as blocking).
- ⚠️ Make work worse ESP when turning (the car may later react to drifts).
- ⚠️ Lead to uneven wear of brake pads, since the vector of application of the braking force changes.
On some vehicles (for example, Volvo S60 or Mercedes C-Class) after replacing disks with a different ET is required recalibration of sensors through a diagnostic scanner.