Generalised rule for verb usage in simple present tense using participle
Solution 1:
As StoneyB has already said, "cars are made" is a passive construction.
In passive voice we always use an auxiliary verb + past participle combination. So, your analysis of Simple Present tense is correct.
Here are a few others.
Present Continuous: Cars are being made [am/is/are + being + past participle]
Present Perfect: Cars have been made [have/has + been + past participle]
Present Perfect Continuous: Cars have been being made [have/has + been + being + past participle] (Passive in Perfect Continuous is rarely used)