4 miles at 12mph (let's be conservative, eh?) is 20 minutes. No wonder the OP thinks it does nothing. I know there are some BFers that 4 miles is a long distance -- and I praise them. Sounds like the OP is adapted enough to do more. So do more.
OP, stop thinking in miles and start thinking in time. You need to be out on your bike (since you picked a cycling forum) for an hour, at least
And since you're sensitive to the diet comments, what is your diet?
[edit] And what's up with asking a question and then being snarky and defensive with the responses?