3P wheel disc types: choosing the right ones for your brakes

The whole point of custom 3-piece wheels is to get literally perfect fitment for your application. The last thing you want is to drop a few grand on some fresh built-to-order rims, wait months for them to arrive, then when they finally show up, you go to test fit one just to find that it hits the brake caliper.

How do you avoid making this mistake? In this article, we’re going to discuss the factors that affect brake clearance, the main one being disk type. We’ll use the universal rule of thumb that there should be at least 3mm of clearance between the wheel and caliper in the tightest area.

These concepts would also apply to monoblock wheels, the difference being that a wheel maker can switch out the lips and or disk type to give you basically any desired width/offset, whereas monoblock wheels are more ‘cookie cutter’.

Quick links

• What is 'Disk Type' anyway?
• High vs low disk
• How to know if 'X' will fit
• Disk types by brand
• Caliper to barrel clearance

What is ‘disk type’ anyway?

Let's start at the beginning. Disk type refers to the shape of the center disk (or 'face') of your multi-piece wheels. These are critical to brake clearance, in particular, brake caliper-to-spoke clearance (or ‘caliper-to-face’).

The other issue could come up when the top of the caliper contacts the barrel of the wheel. This happens when your wheels are too small, more on this later.

A ‘high disk’ will give you more brake clearance, while a ‘low disk’ has less. There are a few ways that wheel makers achieve this:

• Add material to the back pad
• Change the profile of the spokes
• Or, a combination of both

Thicker back pad

What it looks like from the back

SSR GTX01 disk types

Adding material to the back pad is effectively like adding a built-in spacer. Apart from making the lug pockets deeper, as we see in this picture from SSR, the spokes remain the same.

Here’s what a side view would look like (T Disk has the most clearance, W Disk has the least)

Spoke profile  

Advan GT Beyond concave profiles

Another way to add extra brake clearance is to change the profile of the spokes. Sometimes this means more concavity, like we see with these Advan GT wheels. Wheels with a convex spoke (think SSR SP1) will have more curvature, i.e. more of a ‘C’ shape, to give increased clearance.  

Some wheels will feature more back pad AND a different spoke profile to achieve a ‘higher’ disk.

So, a higher disk is always better? Right?

No, not if you care about aesthetics. There’s a proportional relationship between lip size, disk type, and the final offset of your wheel. Lower disk = more visible lip. Higher disk = less lip.

When you’re browsing wheels, for example in our shop, you can choose the disk type and offset, among other specs. Most of the time, you won’t be choosing the lip sizes as this is something that the wheel manufacturer will figure out once you place an order.

So, if you want the largest possible lips, like most do, you would go for the lowest possible disk that still fits your brakes. Rear brakes almost always have more clearance, so you’ll typically see lower disk rear wheels and higher disk fronts (e.g. Work wheels w/ A-disk front & O-Disk rear).

If you’re curious about how much disk type affects lip size, reach out to the manufacturer. They’ll be able to tell you how much disk size changes the lip.

How to know if your wheels & brakes fit

Before busting out rulers and tape measures, start by searching to see if anyone has run the exact same setup in the past. You’ll need to find the same car, with the same brake package, and the same wheels you want.

There’s also a chance the wheel manufacturer might have some useful insight–it’s worth asking.

Of course, you could be dealing with a wheel & brake setup that no one else is running. In this is your situation, we’ll have to do our best to measure.

Unless the wheels you want have perfectly straight spokes (i.e. no concavity or curvature), it’s going to be difficult to 100% guarantee clearance, but we can get close.

When looking at caliper-to-spoke clearance, it comes down to how wide the calipers are, and how far inboard or outboard they mount. If you know nothing about the brake clearance for a given car, the rotors can give you some insight.

Turns out rotors have an offset too. Rotors with a higher offset (more backspacing) will have the calipers mounted more inboard, meaning more clearance. This is a nice rule of thumb if you know nothing else about the platform you're dealing with, but to get some quantitative data, you’ll need some measurements.

How to measure caliper protrusion

Using a ruler and a straight edge, you can measure how far your calipers poke out past the rotor’s mounting surface. If the wheels in question happened to have perfectly flat spokes, your work would be done.

Neither wheels nor calipers are perfectly square; this is why it’s hard to be 100%. However, if you put in some work… okay, a lot of work… you could make a rough ‘profile’ or shape of the caliper. Take as many measurements as you can, use them to make a drawing, then double and triple check.

Once you have a crude drawing of the caliper with dimensions, you can compare this to the manufacturer's drawing of the wheel profiles to see which disk will fit your brakes. Again, due to the complex shapes, this isn’t going to be perfect, but at the very least you should be in the ballpark. Worst case scenario: a small slip-on spacer should sort out minor clearance issues.

Disk types of popular brands

There isn’t a standard naming convention for disk types between brands. Here, we’re going to show how some popular brands name their various disk types.

Work Wheels disk types

This chart breaks it down. Work Wheels offer disk types from T to W, with T having the most brake clearance and W having the largest lip. Originally, there were 3 disk types from Work: O, A, and R; since then they’ve added a bunch more.

SSR wheels disk types

SSR has disk sizes ranging from SL (super low disk) with the largest lips to HP (hyper disk) with the most clearance.

• SL - Super Low Disk (largest lips)
• NR - Normal Disk (equivalent to Work A-Disk)
• MD - Mid Disk (extra brake clearance)
• HP - Hyper Disk (most brake clearance)

Advan Wheels

Advan is all over the place with their naming. Depending on the model, here’s what you might see:

• LO, C-5, SL or HP - low disk
• MD, NR, C-3 or MHI - mid disk
• HI or C-1 - high disk

Caliper to barrel clearance

While we’re on the subject of brake clearance, we’ll quickly mention caliper-to-wheel barrel clearance.

If your wheels are too small, the calipers will hit the barrels. This one is pretty obvious, but if you mess it up the result is the same: your wheels won’t fit. The difference is that spacers won't even help in this case.

In general, for a certain brake package, there will be a minimum wheel size. For example, a 370z with Akebono brakes needs at least 18” diameter wheels. Even then, not all 18s are going to work. Enkei RPF1 18x10.5 +15 are confirmed to fit, while 18” Z32 Touring wheels are confirmed NOT to fit.

Like caliper-to-face clearance, research is key to knowing if your wheels will clear.

All wheels have a drop center, this is the part that lets you mount a tire, but they can be a bit different from manufacturer to manufacturer, wheel to wheel. This is why some wheels will fit over your brakes while others won’t, even if they’re the same diameter.

Step lip wheels have less barrel clearance. 18” step lip wheels will have the same clearance as a 17” reverse lip. And if they’re double-stepped? You guessed it, an 18” double step rim would have similar clearance as a 16”.

The good thing about barrel clearance is that it's super easy to measure.

How to measure for barrel clearance

Here we can take a measurement from the center of the hub to the tallest point on the caliper.

The only real challenge is making sure you’re measuring from the center of the hub. Verify your measurement a few times and you should be good to go.

With this measurement, the wheel manufacturer will be able to tell you if a wheel is a go or no go.

Wrap up

15 years from now hopefully we can 3D scan our brakes using our phones and know which wheels will and won’t fit. For now, the old expression “measure twice, cut once” is kinda applicable here, but it’s more like: “measure 10 times, order once”.

Even then, it's hard to be 100% accurate with wheel-face-to-caliper clearance. The good thing is that as long as you land somewhere in the ballpark, you’ll be fine. Needing a small slip-on spacer isn’t the end of the world. On the flip side, if you blindly order the lowest disk type for maximum lip, you might end up with $4000 paperweights. 

Before you even start measuring, there’s always a chance someone has run the same wheels with the same brakes, and can confirm if they fit or not. The wheel maker, forums, and our Fitment Gallery are all great sources to check.