Ive been using 30mm spacers under my stem for over a year with no problems but I read in someone's answer to an unrelated question that more than 20mm is considered dodgy for the fork steerer! Does anyone know the definitive answer to this?
You will be putting a little bit more stress on the steerer but I doubt it’s anything you need to worry about. Done it myself in the past. Is there anything in the fork user manual relating to spacers?