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Well, there are not many choices because of the vintage rim sizes, and amongst the available tires, there does not seem to be a standout performer other than Avon which is going away. i would get whatever is available locally in the stock sizes if you are trying to fit them under the fenders. If you are building a custom, then you can go taller and maybe a bit wider. A 90/90-18 will fit the same as a 3.00-18 on the front, and a 100/90-18 should do the same in the rear.