What center bore is

The center bore is the big hole in the middle of the wheel. It slides over the hub on your car, the raised ring the wheel sits on.

Every Heritage MonoC wheel has a 73.1 mm center bore. The 6-lug Kokoro-OR has a 106.1 mm bore.

Why 73.1 mm means hub rings

A larger bore fits over more hubs. That is what lets one wheel cover so many cars. The tradeoff is a gap. On most cars the hub is smaller than 73.1 mm, so there is space between the hub and the wheel.

With that gap, the only thing centering the wheel is the lug nuts. That is called lug-centric. It leaves room for the wheel to sit a hair off center. When that happens, you feel it as a vibration, usually at highway speed.

A hub-centric ring fixes that. It is a simple ring that fills the gap between the hub and the wheel. With the ring in place, the hub centers the wheel, the same way it does with your factory wheels.

How to size hub rings

Hub rings have two numbers:

• Outer diameter: matches the wheel. For MonoC, that is 73.1 mm.
• Inner diameter: matches your car's hub.

So a ring for a MonoC wheel reads 73.1 mm to your hub size. Find your hub size in your car's specs, or measure the hub with calipers with the wheel off. Rings come in plastic and aluminum. Either way, the fit should be snug on the hub and snug in the wheel.

Don't know your hub size? Email us your year, make and model and we will help.

Installing them

• Clean the hub face and the back of the wheel. Rust and dirt keep the wheel from sitting flat.
• Press the ring into the wheel or onto the hub, whichever holds it better.
• Mount the wheel and start the lug nuts by hand.
• Torque in a star pattern with a torque wrench, to your car's factory spec. Skip the impact gun.
• Re-check the torque after your first drive.

Offset basics

Offset is the distance, in millimeters, from the center line of the wheel to the face that bolts to the hub.

• Higher offset (a bigger positive number) pulls the wheel in toward the suspension.
• Lower offset pushes the wheel out toward the fender.

Heritage's real sizes show how much it matters. Kokoro comes in 18x9.5 +22 and 18x9.5 +38. Same diameter, same width. The +22 sits 16 mm further out. At the fender, 16 mm is a lot.

Sakura and Imola come in the same two 18x9.5 offsets, so the same math applies. At the far end, Kokoro's 18x11 +6 is wide and low offset. That is an aggressive fitment, the kind that needs room at the fender. On the truck side, Kokoro-OR comes in 17x9 +12 and 20x9 +18.

Width basics

Every extra inch of width adds 25.4 mm. With the offset unchanged, that splits evenly: 12.7 mm more on the outside and 12.7 mm more on the inside.

Change width and offset together and the math shifts. Two examples from the Kokoro lineup:

• 18x8.5 +35 to 18x9.5 +38. The extra inch adds 12.7 mm per side. The 3 mm higher offset pulls the wheel in 3 mm. Net result: the outer lip moves out 9.7 mm and the inner edge moves in 15.7 mm.
• 20x9 +35 to 20x10 +45. The extra inch adds 12.7 mm per side. The 10 mm higher offset pulls the wheel in 10 mm. Net result: the outer lip moves out only 2.7 mm and the inner edge moves in 22.7 mm.

The second one is the lesson. A wider wheel doesn't always poke out more. Sometimes it uses up inner clearance instead, so check your suspension and brakes.

Other clearance checks

• Brakes. Big brake kits need room behind the spokes. Tell us about any brake upgrade.
• Suspension. Coilovers and aftermarket arms change inner clearance.
• Fenders. Lowered cars have less room. Camber and tire size change the picture too.
• Directional designs. On Hokkaido-DIR, all four wheels face the same way. Know that going in.

Bolt pattern still comes first

Center bore and offset only matter once the bolt pattern matches. MonoC wheels come in 5x100 and 5x114.3 on most models, 4x100 on the Kokoro 4-Lug, and 5x127 or 6x139.7 on Kokoro-OR. Heritage also custom drills other 5-lug patterns for $30 per wheel, ready in 7 to 10 business days. Drilling changes the lug holes, not the 73.1 mm bore, so you still need the right rings.

Get it right the first time

Send us your year, make and model, your suspension and brake mods, and the tire size you plan to run. Email info@heritagewheel.com and we will help you pick a size, offset and ring size that work together.

Then shop the MonoC collection. Most orders ship the next business day.