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New to the forum and bikes in general, so apologies if this has already been answered. What is the fork diameter on the 81 GPZ550? From what I’ve found I think it’s 35mm but I wanted to confirm with the pros

1981 Kz550D1 (Gpz) uses 36mm forks.

Strange but true, the later 1982-83 Kz550H1-H2 (Gpz) uses 35mm. The OD is smaller, but the walls are thicker.

Fork tube chart link for future reference. The 550-D1 isn't listed in the pdf, but from the cross-reference at Partzilla
the 81 GPz 550 has the same fork seals as the 550A/C models. same seals = same diameter.

Ohio Cafe Racers Fork Tube Size Chart pdf

Partzilla >> 1981 KZ550-D1 >> Front Forks
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thanks guys!

Like Martin said, the 81 Gpz has same 36mm fork diameter as the Kz550A (standard) and Kz550C (chain-drive Ltd) models.