In case you're not already aware, Metra will not be allowing bikes from Sat. 8/18 to Sun. 8/19 due to expected crowds for the Chicago air and water show. The exception is folding bikes in bags, however, trains may be crowded enough to make even folders a tough squeeze.
If you were planning to take your bike on Metra this weekend, you may want to try CTA or Pace, or find another way to go.