question: What time was achieved on Saturday 29th August by the rider who recorded 25' 01.89 90.438mph on Friday 28th August?
answer: SELECT sat_29_aug FROM table_23465864_4 WHERE fri_28_aug = "25' 01.89 90.438mph"
context: CREATE TABLE table_23465864_4 (sat_29_aug VARCHAR, fri_28_aug VARCHAR)