The Short Version
- 4×100 with a 54 mm hub bore. First-generation bB, second-generation bB, and the first-generation Scion xB — all the same.
- Factory wheel on the JDM Z grade: 15×6J +39 on 185/65R15.
- The first-generation Scion xB is the JDM bB. Same platform, same hub, essentially the same car with a different interior.
- The second-generation Scion xB is not. It is a larger, US-designed vehicle that shares only the name. JDM bB parts will not transfer.
The Name Problem, First
Almost every bad purchase on this car starts with the badge. Toyota sold the NCP30-series bB in Japan from 2000, and from 2004 sold the same car in North America as the Scion xB. That first xB really is a JDM bB: same wheelbase, same platform, same 4×100 hub. If you own one, JDM bB wheels bolt on.
Then in 2007 Scion launched a second-generation xB, and it is a different vehicle. It is longer, wider and rides on a 102.4-inch wheelbase against the original’s 98.4 inches, and it was designed for the North American market rather than adapted from a JDM model. Meanwhile Japan got its own second-generation bB, the QNC20, which is a different car again.
So “bB” and “xB” each cover two generations, and the generations do not line up. If you are buying wheels described as fitting an xB, establish which xB before anything else. The good news is that both JDM bB generations are 4×100 with a 54 mm bore, so within the Japanese lineage you are safe.
Factory Specification
| Model | Chassis | Years | Wheel | Tyre | PCD / Holes / Bore |
|---|---|---|---|---|---|
| bB 1st gen (JDM) | CBA-NCP31, Z X-Version | 2004.04–2005.12 | 15×6J +39 | 185/65R15 | 100 / 4 / 54 |
| bB 1st gen (JDM) | NCP30 / NCP31, various grades | 2000–2005 | 15×6J +39 typical | — | 100 / 4 / 54 |
| Scion xB 1st gen (US) | — | 2004–2006 | 15×6 +38 (factory steel) | — | 100 / 4 / 54.1 |
| bB 2nd gen (JDM) | DBA-QNC20 | 2005–2016 | 14–15 in, grade dependent | — | 100 / 4 / 54 |
The one-millimetre difference between the JDM +39 and the US +38 is a spec-sheet rounding convention, not a real difference. Treat them as the same fitment.
What 4×100 and 54 mm Actually Open Up
This is one of the most common small-car bolt patterns in Japan, which is good news for anyone shopping used. The same 4×100 / 54 mm combination turns up across a large slice of the Toyota and Daihatsu small-car range, so the pool of period-correct Japanese wheels that physically fit a bB is very large.
The constraint is offset, not pattern. The bB sits at +39 from the factory, which is fairly deep. Most Japanese 4×100 aftermarket wheels are made for cars specified around +42 to +45, so a wheel that bolts on may still sit a few millimetres further in than the factory item. For the tall-boy look most bB owners are after, +35 to +42 in a 15×6.5J or 16×6.5J is the practical window. Below about +30 you are into fender work.
Again, 54 mm hub-centric rings are effectively mandatory. Nearly every aftermarket wheel in this pattern is bored much larger.
The Open Deck, and Other JDM-Only Variants
Japan got bB variants North America never saw, and the one that confuses listings most is the bB Open Deck — a pickup-bed-style body that shares the front of the car and replaces the rear. It is a JDM-only trim and has nothing to do with any Scion xB. When a Japanese auction listing says “bB”, it may mean this.
For wheel purposes the Open Deck is still a bB. The thing to watch is load rating rather than fitment: a body configured to carry cargo has different demands on the wheel than a passenger car, and a lightweight aftermarket wheel rated for a small hatchback is the wrong choice for a vehicle being used as a light truck.
What We Could Not Verify
- Wheel width and offset for every individual bB grade. We confirmed the NCP31 Z X-Version directly; other grades came from database search results rather than fetched grade pages, so treat individual offsets as medium confidence.
- QNC20 wheel diameter and offset at grade level. The bolt pattern and bore are confirmed; the wheel sizes are not.
- Whether the four-wheel-drive NCP34 and NCP35 share the identical PCD and bore with the front-drive cars. We found no drivetrain-specific page. No Toyota small car of this era is known to change bolt pattern by drivetrain, but we have not confirmed it here.
Seen on the road
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