The /aɪ/ diphthong is spelled <iCe>, <ie> and <y>. The /ʊə/ diphthong is spelled <ure> or <oor>.
This is a contrast between two diphthongs with different starting positions, different directions of movement and a difference of lip rounding. It is not a problem for learners.
Interesting pairs include:
The density figure is 1.8%. The set makes 10 semantic contrasts giving a loading of 52.6%.
ally allure allied allured allies allures bine bourn bines bournes buy boor buys boors by boor bye boor byes boors guide gourd guides gourds lie lure lies lures shyly surely spy spoor spies spoors tie tour ties tours
John Higgins, Shaftesbury, December 2009