18 x 7.5 with the correct offset will fit nicely, similar can be said with 19's but you need correct offset and tyre load ratings. Load ratings are necessary. also bare in mind legality's. 2 inch's over std rolling diametre. width is limited to 7" but generally 7.5" wont be an issue. any bigger it'll rub anyway. 19's on a classic will ride like shit imho unless you have the suspension/chassis work to suit.

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