* Grinding = roughening the surface with an angle grinder, allowing the pads better hold of the braking surface. * Sounds like a sticky piston. Look on the trials wiki or just hold the other piston while pumping the lever and occasionally spraying a light lube...eg wd40 * Best way to get the ideal tyre pressure is to start at 30 psi...and gradually let the tyre down until you find a pressure you get on with