Figuring out how to measure hub centric rings is usually the first step to solving that dreaded "steering wheel shimmy" that happens right around 60 mph. If you've just bought a fresh set of aftermarket wheels and your car feels like it's trying to shake itself apart, it's probably because the hole in the middle of your new wheels is bigger than the hub on your car. That gap needs to be filled, and to do that, you need two very specific numbers.
It's one of those jobs that sounds technical, but honestly, it's pretty straightforward once you have the right tool. You aren't going to need a degree in mechanical engineering, but you will need to be precise. A hair's width can be the difference between a smooth ride and a vibrating mess.
Why you can't just wing it
Before we get into the actual measuring, let's talk about why you're doing this. Most aftermarket wheels are made with a "one size fits most" approach. Manufacturers make the center bore (that big hole in the middle of the wheel) extra large so the wheels can fit on a variety of different car models.
Your car's hub, however, is a very specific size. If the wheel's center bore is larger than the hub, the wheel is only being held on by the lug nuts. While the lugs do a great job of clamping the wheel to the car, they aren't always perfect at centering it. That's where the hub centric ring comes in. It acts as a shim to bridge that gap, ensuring the wheel is perfectly centered on the hub. If you get the measurement wrong by even 0.5mm, the ring won't fit, or worse, it'll be loose and do absolutely nothing.
Grab the right tools for the job
I'll be blunt here: put the tape measure back in the toolbox. Don't even think about using a ruler or a piece of string. To learn how to measure hub centric rings properly, you absolutely need a pair of digital calipers.
You can pick up a decent set of digital calipers at any hardware store or online for twenty bucks. They'll give you a reading in millimeters down to two decimal places, which is exactly what you need. Since almost all hub and wheel measurements are done in metric, make sure your calipers are set to "mm" and not inches.
Step 1: Measure the vehicle's hub (Inner Diameter)
The first number you need is the diameter of the hub on your car. This will become the Inner Diameter (ID) of your hub centric ring.
Start by jacking up the car and taking one of the wheels off. You'll see the hub—that metal cylinder sticking out from the center of the brake rotor or drum. Before you touch it with your calipers, take a wire brush and clean off any rust, grit, or debris. Even a tiny bit of crusty rust can throw your measurement off by a millimeter, and that's enough to make your new rings not fit.
Once it's clean, open your calipers and place the "outside" jaws (the big ones) across the widest part of the hub. You want to measure the actual ledge that the wheel sits on. Move the calipers slightly to make sure you're hitting the widest point. Write that number down. For many Toyotas, it might be 60.1mm; for many Subarus, it's 56.1mm. Whatever it is, keep that number handy.
Step 2: Measure the wheel's center bore (Outer Diameter)
The second number you need is the diameter of the hole in the back of your aftermarket wheel. This will be the Outer Diameter (OD) of your hub centric ring.
Flip your wheel over so you're looking at the back (the side that touches the car). You'll see the large circular opening in the center. This is the center bore. Take your calipers and use the "inside" jaws (the smaller ones on the top) to measure the diameter of this hole.
Again, make sure you're measuring the actual bore and not a beveled edge or a plastic center cap that might still be clipped in there. Pop the center cap out before you measure. Common sizes for aftermarket wheels are often 73.1mm, 72.6mm, or 66.6mm. Write this number down as your OD.
Step 3: Understanding the ring size
Now you have two numbers. Let's say your car's hub measured 64.1mm and your new wheels measured 73.1mm. When you go to buy your rings, you'll look for a set labeled 73.1 to 64.1.
The first number is always the Outer Diameter (the wheel size), and the second number is the Inner Diameter (the car size). It's a simple "Outside-to-Inside" format. If you see them listed the other way around, just remember that the bigger number is always for the wheel and the smaller one is for the car.
What if my measurements are slightly off?
If you measure your hub and get 56.08mm, but you see rings online listed as 56.1mm, don't sweat it. That's the same thing. Manufacturers usually round to the nearest tenth of a millimeter. However, if you measure 56mm and the only rings available are 54mm or 58mm, you've probably made a mistake in your measurement or you're looking at the wrong part of the hub.
Plastic vs. Aluminum rings
Once you know how to measure hub centric rings and you're ready to buy, you'll notice two main types: plastic (polycarbonate) and aluminum.
- Plastic rings are cheap, they don't corrode, and they're totally fine for daily driving. They're easy to snap in and out. The only downside is that they can get brittle over time with heat, or they might melt if you're doing heavy track days where your brakes get glowing hot.
- Aluminum rings are more durable and can handle high heat better. However, they have a tendency to "seize" to the hub due to galvanic corrosion (basically, the aluminum and the steel hub get stuck together). If you go with aluminum, it's a smart move to put a tiny bit of anti-seize lubricant on the hub before you slide the ring on.
Common mistakes to avoid
Even when you know the steps, it's easy to trip up. Here are a few things I've seen people do wrong:
- Measuring the center cap hole: Some wheels have a decorative cap that sits in a slightly different sized hole than the actual structural bore. Always measure the very back of the wheel where it meets the hub.
- Forgetting the rust: I can't stress this enough. If your car is more than a year old, there's probably a layer of oxidation on the hub. If you measure over that, your ring won't slide on when you actually get it.
- Assuming by brand: Just because you have a "Honda" doesn't mean every Honda hub is the same. While many are 64.1mm, some older or smaller models are different. Always measure your specific car.
- Mixing up units: Some older American wheels might use inches, but 99% of the industry uses millimeters. If your calipers are giving you weird numbers in inches, switch them to metric.
How to install them once they arrive
Once you've used your measurements to order the right rings, installing them is a breeze. Clean the hub one last time. If you got plastic rings, just push them into the back of the wheel. They should be a snug fit; they shouldn't just fall out, but you shouldn't need a hammer either.
If you got aluminum rings, you can either put them in the wheel or slide them onto the car's hub first. I usually prefer putting them on the hub first just to make sure they sit flush against the rotor face. Then, slide your wheel on, tighten your lug nuts in a star pattern, and you're good to go.
The bottom line
Knowing how to measure hub centric rings is a small bit of DIY knowledge that saves a lot of headaches. It turns a shaky, annoying drive into the smooth experience you expected when you bought those fancy new wheels. Just remember: clean the surfaces, use digital calipers, and double-check your numbers before hitting "buy." It's a ten-minute job that makes all the difference in the world for your car's ride quality.