Last Updated on 4 September 2025 by
We know that wheels are one of the most important mods you can do to your car, it’s one of the first things people notice on cars, and always creates conversations about the style, the colour, the fitment, the brand and the car they’re on. They can make you stand out from the crowd or even make you feel like you fit in the community. But how do you know what wheels fit and what the different buzz words mean?
We have pulled on over 50 years of experience in the automotive industry; to create this guide and others, this guide covers the basics but there’re references to other guides we have created that go into even more detail on topics, should you wish to dive a little deeper.
First, we will start with terms you may have heard or seen already; Diameter, Width, PCD and Offset.
Diameter
Diameter will be the one you will be most familiar with, its simply the diameter of the wheel, measured in inches across the face of the wheel, for example 16”, 17”, 18” etc.
Width
The width is the measurement in between the inside beads of the wheel, where the tyre will sit, it’s measured in inches and usually increases and decreases in ½ inch increments. You may also see width shown as a “J” for example 8.5J, this means 8.5 inches wide.
PCD
PCD stands for Pitch Circle Diameter, essentially it is the diameter of the circle made by the wheel bolt holes on your wheels. Generally, PCD will be expressed as a single number, followed by an ‘x’ symbol and then another, larger number. An example would be 5×100. This simply means that the wheel has five bolt holes spaced around a circle 100 millimetres (mm) in diameter. So, 4×108 would mean four holes spaced around a circle 108 mm in diameter and it goes on the same for 5×114 & 5×120 as other examples.
Offset
Offset also known as ET and vice versa, either way they mean the same thing so if you see or hear someone say ET they mean Offset, if you see or hear Offset they mean ET. Every wheel has an offset number such as ET15 or ET45. This refers to the distance in millimetres (mm) between the axle pad of the wheel (the flat plane that mounts against the hub) and the imaginary centre line of the wheel. In simple terms, wheels with a lower offset will stick out more than those with a neutral or positive offset. Check out the diagram below;
Now we will talk about a couple that you have not heard of or considered before but are very important, Centre Bore and Load Rating.
Centre Bore
Centre Bore is the size of the whole in the centre of the wheel that connects the wheel, to the axle on the vehicle via a spigot on the hub. The Centre Bore is usually measured in millimetres (mm), wheels can be a direct fit on the vehicles however on most aftermarket wheels the centre bore diameter is larger in size than the hub spigot which means the wheels need spigot rings to get a closer tight fit.
Load Rating
Every wheel has a load rating and it means the maximum weight that the wheel can safely handle, having wheels that cannot handle the weight of the vehicle (including cargo & passengers) risks the wheel structurally failing, putting yourself and others at risk. Load rating is usually measured in kilogram (KG) and you will need to know the axle weights of your vehicle which is usually found on a plate in a door shut, engine bay or in your vehicle manual.
Wheel Bolts & Spigot Rings
This can be confusing, but luckily, we can help make this simple for you. Every set of wheels we sell, we supply a free fitting kit, this will include bolts and spigot rings (if required.) Wheel bolts come in a variety of lengths and seat types and it will depend on the vehicle and the style of wheel as to what wheel bolts you need, same with spigot rings, depending on the centre bore of the new wheel and your hub diameter will determine if and what size spigot rings you need. How we make it simple is that we will contact you after you purchase a set of wheels, ask you for vehicle details and we will make sure you get the right wheels bolts and spigot rings that you need, with the wheels. It’s that simple.
Where can you find your OE sizes?
So we have told you what the basic specifications mean but how can you find out your OE size or what spec wheel is on your car now, there a few ways to find out that information, the best way is to take one wheel off (or two if you have staggered fitment, front and rear) and look for the specifications (Diameter, Width, Offset, PCD, Load Rating) stamped on the wheels, usually they are on the back of the wheel or inside the wheel barrel, whilst the wheel is off you can also measure your hub diameter for good measure.
Another way is to consult your vehicle handbook and speak with your vehicle manufacturer, they may have a record of the wheel and the wheel specifications that came on your vehicle from factory.
And lastly you can research specifications online via specification website or forums/car club pages however be cautions when using this information and check different sources especially if it’s from other countries as there can be variances in a model depending on the country its sold in.
To find your axle weights, there will be a plate either in one of your door shuts or in your engine bay that tells you, you can also look in your vehicle handbook which should have details of the axle weights for your vehicle.
Staggered Wheels & Changing size from OE
You may have heard the term staggered wheels, staggered fitment or staggered set up, generally this means that the front and rear wheels are different sizes, usually the width and offsets are different so that the rear wheels are wider and depending on the wheel style will have a more concave look. On some performance vehicle models they come from factory standard with a staggered wheel set up, and so if you’re looking for aftermarket wheels you will need to mirror that set up as well, but you can also create a staggered set up on your vehicle if it didn’t come with one from factory.
So now we are talking about changing your wheel specifications from factory, this could be to increase or decrease the wheel diameter, go wider, create a staggered set up etc. to do this there are several considerations, including clearance and the rolling radius of the wheels & tyres combined, amount of camber and so on. We have put together a separate blog that goes into more detail about how to change the size of your wheels, this covers what you need to know and consider. We are also on hand to help you as well to get the fitment you are looking for.
Tyres
Changing wheels is a hugely exciting experience and seeing your car transform will make you feel fantastic. When purchasing a new set of wheels, it would be good practice to get new tyres especially if you are changing your wheel size from OE, this way you get the correct size tyre for your new wheels.
If you purchase a set of wheels and a set of four new tyres for the wheels in one transaction from Demon Tweeks we can mount, valve and balance the tyres to the wheels at no extra cost and then deliver them to you, that means along with the free fitting kit of wheel bolts and spigot rings your new wheels would arrive ready for you to fit.
To help understand tyres sizes and symbols better we have put together another blog called How To Read A Car Tyre. Alternatively, we have a dedicated wheel & tyre sales team that can help create a wheel & tyre package just for you that is the right fitment and delivered to you ready to fit.
Wheel Protection
So you just purchased a new set of wheels, what can you do to look after them, well first things first keep them secure by considering a set of locking wheel nuts, a set of locking wheel nuts come as four nuts (one for each wheel that replaces a standard wheel bolt) and a special key to remove those nuts for maintenance work on the vehicle, without the key someone can’t remove the nut.
Wheel cleaning and sealants is key to keeping your wheels looking fresh, regular cleaning removing brake dust and road grime stops it sitting on the surface of the wheel slowly eating away at it, using wheel sealants after cleaning also adds another layer of protection from road grime and brake dust.
You can get rim protection for wheels in two forms, one being a product like Rimblades can protect your wheel rim from curb rash. Or/and a lesser-known feature of some tyres is that some tyre models come with a form of rim protection for example on the Continental SportContact 7, some sizes have a Flange Rib (FR) which is an extra bit of rubber on the sidewall to help protect the rim of the wheel from curb damage.
Demon Tweeks and what we offer.
Demon Tweeks is not just a website, we have a dedicated wheels & tyres sales team that are on hand to help you find the wheels you are looking for and in the correct fitment, collectively they have decades of experience, they have access to a wide range of brands so they will be able to help you find a wheel design in a fitment you need, whether it’s for a hot hatch, super car, race car or van they will be able to help you, the team also have access to create custom wheels as well so it’s well worth speaking to them about your needs.
If you do purchase wheels on our website our wheels & tyre sales team will contact you to get vehicle and application information to make sure the wheels are going to be suitable, this way you know and we know they are going to fit.
We have mentioned a couple of times in the blog about us delivering the wheels to you but if you live close enough to us in Wrexham or you don’t mind a road trip to our treasure trove of a showroom, we can fit the wheels & tyres for you in our fitting centre.
More Info
Hopefully this blog has given you understanding on the basics about wheels and considerations when purchasing. If you wish to dive further, we have other blogs on different topics that you will find interesting, below is a list of some for you.