What Is a Hub Bore.
And why it matters more
than you think.
Most people look at bolt pattern, wheel size, and offset — and assume that's enough. It isn't. The hub bore is the measurement most people ignore, and the one that causes the most problems.
Most people don't think about the hub bore.
They look at bolt pattern, wheel size, maybe offset, and assume that's enough to get the fitment right. Then they fit the wheels and go.
Sounds simple, right?
It isn't.
We machine wheel spacers every week at Brightstone Engineering, and this is one of the most common issues I see. If the hub bore size is wrong, you can end up with vibration, poor fitment, and a car that never quite feels right.
So let's go through it properly.
What Is a Hub Bore
The hub bore is the hole in the centre of the wheel. It fits over the hub on the car and controls how the wheel sits.
You might also hear it called the centre bore or wheel centre bore, but it all means the same thing.
Every car has a specific hub bore diameter, and every wheel is designed to match that size. For example, many BMW models use a 72.6mm wheel hub bore, whereas other brands use different sizes.
The key point is simple. The hub bore size must match the hub exactly.
| BMW E/F-series | 72.6mm |
| BMW G-series | 66.6mm |
| Audi (MQB) | 66.6mm |
| Mercedes-Benz | 66.6mm |
| Porsche 911 / Boxster / Cayman | 71.6mm |
| Aston Martin (classic) | 68.1mm |
| Aston Martin (modern GT) | 75.1mm |
| Alfa Romeo / Maserati MC20 | 65.1mm |
What Does the Hub Bore Actually Do
The hub bore centres the wheel.
When you install a wheel, the hub locates it in the correct position. Then the bolts clamp the wheel in place. The bolts do not centre the wheel — they only hold it tight.
This is how the hub and wheel alignment is designed to work.
If the wheel is centred correctly, it rotates smoothly. If it is even slightly off, you will feel it when driving.
The hub centres the wheel. The bolts clamp it. These are two separate jobs, and the bolt threads were never designed to do both. When the hub bore is wrong, the bolts are forced to do a job they weren't engineered for.
Why Hub Bore Size Matters
The hub bore diameter controls how well the wheel fits onto the car.
A correct fit should feel tight and precise, with no movement at all between the wheel hub and the wheel.
If the hub bore size is too large, the wheel does not sit properly on the hub. It can move slightly during installation, and the bolts end up centring it instead.
I see this a lot. People come to me with wheel vibration after fitting spacers, and they assume it's a balancing issue. In many cases, it comes back to an incorrect centre bore.
At low speed, it might feel fine. At higher speed, that small misalignment becomes a noticeable vibration.
If the hub bore is too small, the wheel will not fit at all. There is no workaround here. The size has to match.
Wheel vibration after fitting spacers is frequently diagnosed as a balancing problem and sent for rebalancing — which does nothing. If the wheel hub bore does not match, the wheel is not centred. Balancing cannot fix runout caused by incorrect bore sizing.
Hubcentric vs Lugcentric Fitment
This is where the terms come in.
The wheel is centred by the hub. The centre hub lip locates the wheel, and everything stays aligned. This is how the car was designed to work from the factory. The hub carries the weight; the bolts clamp.
The wheel is centred by the bolts instead. That usually happens when the wheel centre bore does not match the hub correctly. You can sometimes get away with it — the car might feel fine at first — but it is not consistent, and it often leads to wheel wobble at speed or vibration.
How Wheel Spacers Replicate the Hub Bore
Once you add a spacer, the wheel no longer sits directly on the hub. The spacer now becomes part of the hub and wheel interface.
That means it has to replicate the hub bore and the hub lip exactly.
A proper spacer will:
- Fit tightly onto the hub
- Provide a matching centre bore for the wheel
- Maintain correct hubcentric fitment
When I machine spacers, the hub bore tolerance is one of the most important parts of the job. Even a small error here will show up once the wheel is rotating.
This is why using proper hubcentric wheel spacers matters: they recreate the original hubcentric fitment, so the wheel stays aligned just as it would from factory.
Every Brightstone spacer is machined to ±0.02mm on the centre bore. That's what eliminates vibration and keeps the wheel running true at motorway speeds. It's not approximate — it's exact.
Common Problems Caused by Incorrect Hub Bore
When the hub bore is wrong, the symptoms are usually easy to spot. Most of the time, people assume it's a balancing issue. But if the wheel hub bore does not match properly, the wheel is not centred. Balancing will not fix that.
In my experience, this is one of the most common causes of repeat fitment problems. People go back for rebalancing, get no improvement, and never identify the root cause.
How to Measure Your Hub Bore
There are two simple ways to find your hub bore size.
First, check manufacturer data. Most brands publish the hub bore diameter for each model. The table earlier in this article covers the most common UK fitments.
Second, measure it directly using a vernier caliper. Measure the hub on the car or the wheel centre bore itself.
You are looking for an exact match. Even small differences in hub bore measurement can lead to issues once the wheel is fitted and rotating at speed.
Real Example: Porsche Fitment
Porsche is a good example of why this matters.
The tolerances are tight, and the steering feel is very precise. If the car hub bore and wheel do not match properly, you will feel it straight away.
I've seen cases where people fit spacers with a loose centre bore, and the result is instant vibration. With a correct hubcentric fitment, everything works as expected. The wheel sits perfectly on the mounting hub, and the car drives cleanly.
If you are running a Porsche, using the correct setup is key:
The same principle applies to every other platform. BMW, Audi, Mercedes, Aston Martin — the hub bore must match. If you are not sure of your exact specification, contact us and we will confirm the correct bore before machining.
Choosing the Right Hub Bore Setup
If you want to avoid problems, keep it simple.
Match the hub bore size exactly. Use parts that maintain proper hubcentric fitment. Avoid generic spacers with loose tolerances.
If the wheel locates correctly on the wheel hub, the rest of the system works as it should.
Final Thoughts
The hub bore looks like a small detail, but it controls how the wheel sits on the car.
Get the hub bore size right, and the car drives smoothly with no issues. Get it wrong, and you end up dealing with vibration, poor fitment, and ongoing problems that don't get fixed by balancing.
From what I see day to day, most of these issues come back to ignoring the wheel centre bore and how it interacts with the hub.
Focus on that first, and you remove the majority of fitment problems before they even start.
Spacers machined to your exact hub bore
Every Brightstone spacer is CNC-machined to ±0.02mm on the centre bore. It fits your hub exactly — no play, no vibration, no compromise.
