Looking for a brand-new set of shiny rims? Or maybe go an inch up or down your car's original rim size?
In that case, you already know that you need to consider several things when shopping around for rims, and correct rim size is one of those things. Unfortunately, rim sizing can get very confusing, but don’t worry, this guide will make it easy for you.
When reading rim size labelling, you need to find the width, diameter, offset, and backspacing measurements. You can find those measurements on the rim markings or by measuring them yourself. Once you have them, finding the correct-size rims for your car will be a breeze.
Ready to have rim size explained to you? Let’s get started.
Are Rims and Wheels the Same Thing?
First, we should clear the air on something that causes plenty of confusion regarding the lower part of cars. A question you’re likely to have on your mind at some point is, “Are rims and wheels the same thing?”
Well, yes and no. For starters, the sections of your car that touch the road consist of several parts, and each part has a particular function. The problem is that some of their names are used differently, depending on where you are in the world and who you're talking to.
Generally, many people use the terms ‘rims’ and ‘wheels’ interchangeably when referring to the metal part around which you wrap your rubber tyre. However, there is some debate about the precise usage of those two terms.
For instance, some people might call the whole unit a ‘rim’ or a ‘wheel’. Others might use the term ‘rim’ to refer only to the outer part of a steel or alloy wheel, not the whole thing itself.
The difference in those two terms isn't too much of a big deal. Even if you talk to a person who uses another word for rim, both of you will understand what the other means when talking about a wheel's size, for instance.
One thing’s for sure, whether you choose to call it a rim or a wheel, there’s zero debate about the name of the rubber part that wraps around it, i.e., the tyre. That’s a universal term for which there are no alternatives. Except for spelling, of course, which is ‘tire’ elsewhere.
Is Rim Size the Same as Tyre Size?
No, the rim size is not necessarily the same as tyre size, though they are closely related.
Note: For lack of a better photo, the image shown above is an example of tyre size code or markings. I'll change that photo as soon as I get the chance to remove one of my car's rim.
You see, car rims of a particular size can be used with tyres of various sizes, so long as the middle of the tyre matches that of the rim. Still, there is a limited range of tire width that can fit every rim size.
Understanding Rim Size
Understanding your rim size is crucial for several reasons, such as fitting rims onto your car and choosing the correct size tyres for them. So, we'll look at where to find the rim size marked on your rims, how to read those markings, and how to measure them yourself.
Where to Find the Rim Size
You can find all the information you need about your rim size stamped on the rims themselves. The rim size markings are typically located on the back of the hub on the rim. Since it’s on the back, away from plain sight, you might need to exert a little effort to get a good look at the markings.
Here's a little hack: Once you've figured out where the marking is (by feel, for example) but can't see it from the correct angle, try using your smartphone camera to carefully snap a photo of it.
That marking will tell you three things:
- Diameter
- Width
- Bolt pattern
How to Read Rim Markings
Locating the rim size markings isn’t too challenging. Unfortunately, understanding how to read rim size from those markings is a different story.
Remember that there’s limited space for the manufacturer to list down all the rim characteristics, which is why they have to use codes instead. The best way to help you understand this is through an example.
For instance, you might find rim markings that say:
7.5Jx16H2 ET 35 |
Here’s what a marking like that would mean:
- 7.5 refers to the rim width of 7.5 inches
- J refers to the flange contour “J” mark
- 16 refers to the diameter of 16 inches
- H2 refers to the inside hump design H2 mark
- ET 35 refers to the offset of 35 millimetres
Since the focus of this article is on rim sizing, your focus will be primarily on the pair of numbers on the first row, which in this case are 7.5 and 16.
Again, a rim marked 7.5Jx16H2 has a width of 7.5” and a diameter of 16”.
How to Measure Rim Size
Relying on the rim size marking is good enough for most people. However, it’s also understandable if you want to know how to measure rim size yourself.
First, find yourself a tape measure. Second, you should know where to start and end your measurements, depending on what you're looking for.
Here are the measurements you can get from your rims and how to do them:
- Diameter: Here, you should always remember not to measure from one outer lip to the other, as that's inaccurate. Instead, you should measure from the top to the bottom of the wheel's hoop. You won't have a place to rest the end of your tape measure, so you'll have to estimate the start and endpoints.
- Width: Like measuring the diameter, you can't get an accurate width by measuring the farthest point from the back to the front. Instead, start your measurement from the bead seat on one end to the other.
- Offset: When measuring the offset, use your tape measure to get the distance from the centre line to the mounting hub surface of the wheel. Note: Measure this part in millimetres (mm), not inches like the other parts.
- Backspacing: To measure backspacing, start from the back pad to the outer lip of the rim.
Now that you know how to read rim size accurately, you can shop for brand new rims much more easily. Check out the Directory over at carpart.com.au to look for local dealers that will have your next pair of brand-new rims!
By Ray Hasbollah