The width, offset and inner and outer barrel sizes on vintage JDM wheels were one of those things I always thought were somehow correlated, but never invested time into this. I ran into a very interesting classified ad on Yahoo Auctions for some SSR Formula Mesh wheels, and it caught my attention because of the sizes. I started to investigate and ran into an article on Kaido Racer blog, explaining the SSR size. Thanks to their article, it all became much clearer now how there is a relation between wheel size, offset and type.
JDM Wheel size types
In general, vintage JDM wheel sizes are often advertised as type A, type B and type C. The most common ones are type A and type B, and the reason why will become clear soon. These types will denote the inner barrel of a wheel, so that’s the part of a three-piece wheel that is on the inside. The size of the barrel is 4 inches for type A, 4.5 inches for type B and 5 inches for type C. As wider wheels are less common, the type C variant will also be less common. As the centre section of the wheel will be mounted against the two barrels, this determines the place where the back of the centre section will end up.
That’s also the reason why there is a strong correlation between the width, types and the offset. Keep in mind that there is a slight variation among brands and designs. For instance, the SSR Star Shark design is slightly more positive offset than the SSR MK I, II and III wheels. In theory, you could just take the Formula Mesh centre section and swap that onto a Mk III outer and inner barrel, and you would end up with the same wheel as it was originally.
Table of JDM Wheel sizes
| Type A | Type B | Type C | ||||
| Width | Lip width | Offset | Lip width | Offset | Lip width | Offset |
| 6.0J | 1.5 inch | 13 | – | – | – | – |
| 6.5J | 2.0 inch | 6 | 1.5 inch | 19 | – | – |
| 7.0J | 2.5 inch | 0 | 2.0 inch | 13 | 1.5 inch | 25 |
| 7.5J | 3.0 inch | -7 | 2.5 inch | 6 | 2.0 inch | 19 |
| 8.0J | 3.5 inch | -13 | 3.0 inch | 0 | 2.5 inch | 13 |
| 8.5J | 4.0 inch | -19 | 3.5 inch | -7 | 3.0 inch | 6 |
| 9.0J | 4.5 inch | -25 | 4.0 inch | -13 | 3.5 inch | 0 |
| 9.5J | 5.0 inch | -31 | 4.5 inch | -19 | 4.0 inch | -7 |
The correlation between the wheel width, type and offset is quite apparent in the table above. It also makes sense that the type A wheels have a lower offset as they have a smaller inner barrel, which then means the outer barrel has to be bigger to get to the same width.
Table with corrections per brand and/or design
| Brand | Design | Offset compensation |
| SSR | Formula Mesh | -3 |
| Longchamp XR-4 | ranges from +1 to +3 | |
| RS Watanabe | 8 spoke | type A: +3, type B: -4 |
| Yokohama Advan | A3A, A3B | Most as type A, some as type B |
| Focus Racing | As type A: -2 | |
| Volk Racing | Most as type A: +2 |
Then a special nod to the previous JDM wheels I had on the AE86: the Yokohama Almex Y3B. The Almex Y3A and Y3B wheels seem to have a consistent outer barrel and vary in the inner barrel. The 6.0J wheel is similar to the SSR type A with an offset of 12. The 5.5J wheel has an offset of 6, which means the inner barrel has to be 3.5 inches wide.
I hope my explanation makes sense and that it will help someone in the future. If you have specific JDM wheel sizes you wish to share, leave a comment below!
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