We had Velocity rebuild the wheels on our tandem with one of their more robust rims, Atlas. 20"/406 , 36h front, 26"/559, 40h rear. Both on Velocity hubs. Neither of us are extra large, but there are 2 of us on a 45+ pound bike. Atlas rim also available in 700c/622.
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Bacchetta Giro A20, RANS V-Rex, RANS Screamer