Just wondered if anyone new the answer to this.
Took the bike out to Cannock chase and as usual I took the wheel off to get it in the car. Came back and could not get the wheel back on because the pads were too narrow for the disc. Any ideas how to sort this and y it happens?

PS: the brakes are hydraulic

Put something between the pads and gently prise them appart (blunt old flat blade scrwdriver), the pistons will go back into the calipers. You must have touched the brake and the srprings are not strong enough to push the pistons back alone, maybe you should work the pistons in and out a bit to make sure they are free.

Brake lever got pressed most likely. To stop it, just wedge some cardboard or something between the pads when the wheels not there. Easy enough to sort with a tyre lever, just prise them apart.