Speaking as a self-appointed internet expert, I'd say either 23 or 25mm internal would be best for a 42mm tyre.
I'd get Stan's crest rims, the new version. 23 mm internal, very light and easy tubeless.
@Netakure started
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Speaking as a self-appointed internet expert, I'd say either 23 or 25mm internal would be best for a 42mm tyre.