Wheel Guides
Custom Wheel Fitment Guide: Offset, PCD, Width Explained
Buying wheels without understanding fitment is how you end up with a set that rubs the fender, sits too deep in the arch, or won't clear the brake caliper. This guide covers every measurement that defines whether a wheel fits your car — and how to get each one right before ordering.
The Four Measurements That Define Wheel Fitment
Every wheel fitment comes down to four numbers. Get all four right and the wheel fits. Miss one and you're dealing with rubbing, incorrect spacing, or a wheel that won't bolt on at all.
1. Diameter
The wheel diameter in inches — 18, 19, 20, 21. This determines which tire sizes you can run. Increasing diameter requires a lower-profile tire to maintain the same overall rolling radius (and therefore the same speedometer reading and suspension geometry). Most modern performance cars run 19–21" from the factory; stepping up one size is common for aesthetics and handling without significant downsides.
2. Width
Measured in inches across the inside of the barrel (bead-to-bead, not the outer lip). Width determines the range of tire sizes you can safely mount — a 9" wide wheel typically runs 245–265mm tires, a 10" wide wheel runs 275–295mm. Wider wheels allow wider tires for more grip, but require more clearance from the fender and suspension components.
3. Offset (ET)
This is the most misunderstood measurement in wheel fitment. Offset is the distance in millimeters between the wheel's mounting face (where it bolts to the hub) and the centerline of the wheel barrel.
- Positive offset (ET+): Mounting face is toward the street side of the wheel. The wheel sits deeper in the arch. Most modern FWD and AWD cars run high positive offset (ET35–ET50).
- Zero offset (ET0): Mounting face is exactly at the centerline.
- Negative offset (ET-): Mounting face is toward the car. The wheel sticks further out. Common on wide-body builds and older RWD platforms.
Lowering the offset (going from ET35 to ET20, for example) pushes the wheel outward toward the fender. Raising it pushes the wheel inward toward the suspension. A few millimeters in either direction can be the difference between a perfect flush fit and rubbing.
4. PCD — Pitch Circle Diameter
The bolt pattern. Expressed as number of bolts × circle diameter in mm — for example, 5×112 (five bolts on a 112mm circle) is standard for most Audi, BMW, and Mercedes models. 5×114.3 covers most Japanese performance cars. PCD must match exactly — a wheel with the wrong bolt pattern physically cannot be mounted safely.
Center Bore: The Often-Forgotten Measurement
The center bore is the diameter of the hole in the center of the wheel that fits over the hub. OEM wheels are hub-centric — the center bore matches the hub exactly, so the wheel is centered by the hub, not the bolts.
Aftermarket wheels are sometimes made with a larger center bore to fit multiple hub sizes, then centered with plastic hub rings. This works, but hub-centric fitment is always preferable — particularly at high speed, where an off-center wheel creates vibration that no amount of balancing will fix.
All 6061 WORKS wheels are machined to your exact hub bore — no rings, no compromise.
How to Find Your Car's Fitment Specs
Three reliable sources:
- Door jamb sticker — lists OEM tire size, which tells you the OEM wheel diameter and width
- Owner's manual — lists approved wheel sizes and offsets
- For custom fitment beyond OEM specs — wider wheels, aggressive offset, flush fitment — you need to account for suspension clearance, fender clearance, and brake caliper clearance. Send us your car model and we'll pull the exact baseline specs and calculate from there.
For custom fitment beyond OEM specs — wider wheels, aggressive offset, flush fitment — you need to account for suspension clearance, fender clearance, and brake caliper clearance. This is where a few millimeters of error becomes expensive.
Calculating the Right Offset for Your Build
The key formula:
New offset = OEM offset − (width increase ÷ 2)
Example: Your car runs 8.5" wide wheels at ET35. You want to go to 9.5" wide while keeping the same outer lip position:
Width increase = 1" = 25.4mm. Half of that = 12.7mm.
New offset = 35 − 13 = ET22
This keeps the outer face of the wheel in the same position relative to the fender. The extra width goes inward toward the suspension — which you then need to verify clears the strut, spring, and inner fender.
Brake Caliper Clearance
Upgraded brakes — Brembo, AP Racing, Akebono, StopTech — are larger than OEM calipers and require more clearance from the wheel spokes. A wheel that fits a stock-brake car may foul a big brake kit by 2–3mm.
There are two ways to check before ordering:
- Caliper clearance templates — cardboard cutouts matching your caliper's profile, held against the wheel to check clearance
- Specify to your wheel manufacturer — provide your brake brand and model, and the wheel is designed with verified clearance built in
This is standard practice at 6061 WORKS. Every set is spec'd with your brake setup confirmed before a cut is made.
Common Fitment Mistakes
Ignoring the inner barrel clearance
Wide wheels with low offset can contact the suspension strut, spring, or inner fender liner. Outer clearance gets most of the attention, but inner clearance fails are more common — and harder to fix without spacers or offset changes.
Using spacers to compensate for wrong offset
Spacers are a compromise. A 10mm spacer effectively reduces offset by 10mm and adds 10mm of hub extension — which puts more stress on the wheel bearing and hub. For occasional track days, quality hub-centric spacers are acceptable. As a permanent fitment solution for a wheel that's simply the wrong offset, they're not.
Matching diameter but ignoring width
A 19" wheel in the right diameter but wrong width will either run a tire too narrow (poor grip, poor aesthetics) or mount a tire outside the safe width range (handling instability, sidewall stress).
Frequently Asked Questions
What offset should I run for a flush fitment?
It depends entirely on your car's fender width, suspension geometry, and wheel width. There's no universal answer. The correct approach is to calculate from your OEM specs using the formula above, then verify inner clearance before ordering. Our engineers do this calculation for every order.
Can I run different offsets front and rear?
Yes — staggered setups (different width or offset front vs rear) are common on RWD platforms. Many BMW, Porsche, and Ferrari models run staggered from the factory. Front and rear specs are calculated independently.
What happens if the center bore is too small?
The wheel won't seat on the hub. If the center bore is too large, the wheel is centered by the lug bolts alone — which creates vibration and puts shear stress on the hardware.
Does offset affect handling?
Yes. Offset affects the scrub radius — the distance between the wheel's contact patch centerline and the steering axis. Large changes in offset from OEM spec can alter steering feel and stability. For most street builds within 15–20mm of OEM offset, the effect is minimal.
Our Approach
Send us your car details and brake setup — we calculate offset, center bore, and spoke clearance before manufacturing starts. Custom forged monoblock, DDP worldwide.