Wheel center bore.
First, let's start by explaining what the center bore is, if you haven't been following our previous blog posts. The center bore is the hole in the middle of the rim, the diameter of this hole. See below.
Wheel center bore = the large hole in the middle of the rim.
Here's a picture of the inside of a wheel, the center bore is the hole in the center of the five bolt holes / lug nut holes which goes around it.
The center hole diameter is easy to measure, use a measuring tape or a caliper, which the latter is more preferred.
The center bore of a rim must have the same measurement as the wheel hub of the car it will mount on, which automatically enters the topic of hub centric rings or drilling the center bore.
Hub centric rings / spigot rings.
As we said above, the wheel center bore must match the wheel hub dimension, or else the wheel simply won't fit. So, what can we do if the center bore of the rim is either too large or too small? Well, it's pretty simple, if it's too large you can use hub centric rings also called spigot rings (or center rings, centric rings, etc.), to make the center bore the correct measurement (converting a large center bore to a smaller size). Below you can see what spigot rings looks like, one ring are used for each wheel.
Often, aftermarket wheels are manufactured with a very large center bore, so it will fit many different cars by using hub centric rings.
The spigot ring is in place, although it was slightly too large for this rim, but you get the idea.
The hub centric rings will both make it easier to mount the wheel by keeping it in place when bolting it up, and also prevent it to shake / wobble during driving, although it isn't that common if you manage to mount it without any trouble, it is always a very good idea to use centric rings, we highly recommend it, they aren't expensive either!
Oops, almost forgot to mention that hub centric rings can be made of either ABS plastic or aluminum material. We prefer ABS plastic as it won't get covered with verdigris as aluminum rings can and thereby get stuck to the wheel or wheel hub.
But, what if the center bore on the other hand is too small, we can't use any spigot rings then, can we? No we can't of course, unless they are some magical rings. The alternative in that case is to drill the hole larger, by using a milling machine or a very, very precise drill. This will often require a workshop as the tooling is pretty expensive. This scenario isn't that common though, as the center bore for most aftermarket wheels often is larger than the wheel hub dimension of the car, but one example may be if you own a BMW e39 and wants to fit a BMW e46 M-rim, then the center bore of the 3-series wheels has to be made larger.
That's all for now, drive wobble free by using spigot rings, and until next time, take care!