If the goal is to go fast, you have to factor in aerodynamics along with rolling resistance.
Most aero wheels these days are optimized for 25mm tires. Admittedly there’s not a lot of tandem specific data. That said, my bet is the fastest overall option is a 25-28 mm tire on a rim optimized for that size tire.
Depending on your rims and how fast you ride, I think going wider than 1 1/4”, (32mm) is very unlikely to make you faster.
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You could fall off a cliff and die.
You could get lost and die.
You could hit a tree and die.
OR YOU COULD STAY HOME AND FALL OFF THE COUCH AND DIE.
Last edited by merlinextraligh; 01-23-21 at 05:04 PM.