Hre is what Steven Pinker, (Author of The Language Instinct and Words and Rules (Formerly at MIT, now at Harvard)) has to say about the pronunciation of irregular verbs:
Since irregulars are unpredictable, people can't derive them on the fly as they talk, but have to have memorized them beforehand one by one, just like simple unconjugated words, which are also unpredictable.
You can read the entire article here:
http://pinker.wjh.harvard.edu/articl..._landfall.html
I hope that helps!
eric