Wheel Basics

We really don’t think of our wheels much considering what they do. We take for granted that they hold the tires on and don’t think of them doing anything else. However, your wheel has a lot of technology involved in their construction, design, and other elements beyond tire retention. Here are some basic things you need to know about when it comes to your wheels on your Jeep.

First, let’s talk about what your wheels do and how they do it. When we say “wheel,” we are talking about the part that many people call the “rim.” On a technical standpoint, a wheel isn’t a rim because a rim implies an outer edge. For the sake of keep the article as simple as possible, we will use the term “wheel” for the rest of the article. Continuing the topic, the basic premise is that wheels hold on to the tires and that’s not a wrong way to think. However, that’s not the complete story as tire retention is a major part of the design of your wheels.

Wheel Design

Yes, there’s more to being a wheel besides round and shiny. When your tire is off, you’ll notice quite a few features that you don’t take into consideration when it is on. So, when we describe your wheel, “outside” will reference the side of the wheel you see from outside your Jeep when it’s installed. “Inside” will reference the side of the wheel that you can’t normally see as it sits closer to the body.

On each end of your wheel are flanges, where the tire sidewall seems to sit when it’s installed. Just past it, however, is where the real tire retention is done known as the bead seat. Each side of the wheel has one – one for the outside and one for the inside of the wheel. Before heading to the wheel center, there is an additional hump that works to retain the bead of the tire on the wheel. The only exception to this is the beadlock, which we’ll get into in another article.

The center of your wheel has a strange looking drop just past the outside bead seat. This is known as a “Tire Well” or “Drop Center.” The drop allows the tire installer to install the inside bead of the tire on the wheel without overstretching it. Doing so can damage the bead and cause many issues from air leaks to full tire failure at the bead. Once past the outside bead seat, the outside bead can then be installed, and the beads seated by a rush of air.

For wheels with a large “dish” – where the wheel face is closer to the center of the wheel rather than right on the outside wheel flange – or has a wide-lip, the drop center can be on the back side of the wheel. The purpose is the same, just inverted so the wheels must be mounted and dismounted from the inside of the wheel rather than the outside.

Valve Stem

The valve stem is how your fill and remove air from your tire when it’s mounted to the wheel. There are many different types of valve stem hole designs to match different valve stems. An aluminum stem won’t normally be able to be mounted to a wheel where the stem is rubber. That’s not always the case as there are aluminum valve stems that are designed for rubber stem holes, but not the other way around (rubber stem designed to be used on an aluminum stem hole).

Some wheels are also designed for reusing Tire Pressure Monitoring System (TPMS) sensor valve stems, too. When you order your wheel, you will want to be sure which valve stem design you’ll get while also making sure that your Jeep’s TPMS system will work with the wheel.

How a Wheel is Sized

In the Jeep world, sizing of a wheel will read like this: 17x9.0 BS: 5-inches.

The first number is the wheel’s bead seat diameter. The flanges add an additional 0.70-inch to 1.4-inches to the overall diameter. However, these are not measured because it’s where the beads seat to the wheel rather than the flange height because of that range.

The second number is the width of the wheel from flange to flange. These numbers run in 0.5-inch increments, so you’ll see 8.0, 8.5, 9.0, and so on.

That last number references the backspacing (BS) of the wheel. This is measured from the inside flange to the mounting hub of the wheel. These are normally done in 0.25-inch increments. So, you’ll see a 4.5, 4.75, 5.00, and so on.

However, you will also see sizing from overseas manufacturers done like this 17x9.0 0, 17x9.0 +45, 17x9.0 -15. Instead of backspacing, these manufacturers are using offset measurements. The idea is still roughly the same, it’s telling you where the mounting hub of the wheel is, but this measurement is in relation to the center of the wheel rather than a measurement from the inside flange. Those numbers will also be in metric, so a +45 would be 45mm from the center of the wheel going towards the wheel face while -45 would be 45mm from the center of the wheel going towards the inside flange.

The good news is that these measurements can be converted very easily. First, you need to know the rated width of your wheel which is the 9.0 in our example above, then then add another 1-inch to that measurement, and then divide that in half. The flange of the beadseat adds a 0.5-inch to the width of the wheel on each side, which is why you add 1-inch to your initial measurement as you have two flanges. This will be our base measurement and where 0 offset will be. You'll then account for the offset measurement.

That 17x9.0 5-inches backspaced wheel at the beginning of this explanation will be a 0 offset in this example (9-inch rating plus 1-inch for the flanges, then divide by two which will give you 10/2=5-inches). A 17x9.0 BS 4.5-inches will be a -13 offset, 17x9.0 BS 5.5-inches will be +13mm offset, 17x9.0 BS 4.75-inches will be -6 offset, and a 17x9.0 BS 5.25-inches will be +6 offset. So, as you can see, every 6mm of offset will be roughly 0.25-inches to add (positive offset) or subtract (negative offset) from your wheel’s centerline to get your backspacing conversion and vice versa.

If that still feels kind of confusing, here is a chart to help you out.

Lug Nuts and Center Hub Bore

Finally, we need to talk about how your wheel’s hub mounts to your axle hub. It’s not just simply a lug nut and that’s it. The lug nut is designed in a specific way to facilitate the mounting of the wheel to your Jeep. The common aftermarket and your OEM Jeep lug nut will be an “acorn” design with a 60-degree conical seat.


Some wheels, like those from Ford and Toyota, use a flat mount rather than a conical seat and are known as Mag Seat. This is because those wheels are hub centric, where the wheel centering is done by center hub rather than the lugs. A wheel that uses the lug nuts for centering would make a wheel “lug centric.”

Some wheels also require a short-shanked end known as the Extended Thread (ET) style. This allows for more threads of the lug stud to engage with the lug nut for a more secure, stronger retention. These can have different seats as well like the Mag style, conical, and ball seats. So, buy the proper lug nuts to match what your wheels require. However, if you have extended lug studs to work with a set of slip-on spacers, you’ll want to consider buying either an open-ended lug nut or a taller lug nut rather than ET or standard-length lug nuts.

Conclusion

So, as you have learned, there is so much technology that goes into wheel design. It’s not just about being a pretty face that holds on to your tire. Your wheels do so much to ensure your safety as well as the looks of your Jeep. Next, we’ll talk about the different types of wheel construction along with what everyone wants to install on their Jeeps – beadlock wheels.