S before i more closely corresponds to English 'sh'.
t (before i)
t
tiimu 'team'
T before i more closely corresponds to English 'ch'.
"...one-fourth of all the characters used in modern Japanese occur in three-fourths of all the most frequently occurring words. This means that by concentrating on learning approximately 500 select characters, the student is assured of being able to read 75% of all the high-frequency words he will encounter in modern literature." - The Kanji Way to Japanese Language Power.