"What wheel" could be correct. As in "I can't see the wheel" - "The wheel? What wheel?" But only then and this in not the intent of the lessons I presume :)
For those who wonder about when to use "what" vs "which" in English: http://www.pearsonlongman.com/ae/azar/grammar_ex/message_board/archive/articles/00052.htm
"Which tire" could also be correct, no? In Canada we call the 4 things on our cars tires anyway.
I said "which tyre" and was marked wrong....Generally speaking ρόδες in Australia refers to to car tyres....