Was just looking at a spoke calculator for a wheel I am going to build, and when I clicked on extra information it gave a differential of 80%.
How does that work? Wouldn't the rim just move towards the more tensioned side and even out the tensions?
Yes, exactly.
Your hub spoke flanges are offset to allow for cassette and/or rotor mount, so the different tensions set up a dish in the wheel so the rim ends up central in the dropouts.
go and ping a spoke or three on the drive side of your back wheel , then the non drive side.
Ping, pong.
It's to do with the spoke angle to the flange. Steeper (more vertical = tighter)
Think about guy ropes for a tent, the closer they are to the tent, the tighter they need to be to have the same effect as one pegged further away, I guess.