How old are you? What is your normal activity level? Is your job sitting or active? I've been where you are (well, I'm 5'10 and was a bit heavier than you).
Start tracking every bit of your nutritional intake (I use dailyplate.com). Every Popsicle, glass of water, m&m, etc. If you're an average American you'll be surprised how much you overeat EVERY day. I use to average about 3400/day. You need to change your lifestyle, not just go on a diet for a few months. Yo-yo weight ain't good for your heart.
An average adult male over 30 needs about 2100 calories per day if moderately active. Any more than that adds pounds. If you want to loose weight about 1800 per day is the ticket for loss of about 1-2 lbs per week. If, on top of your other activity, you ride 18 miles in 1 hour you've burned about 600 extra calories (800 burned - 200/hr normally burned during day), which for me means I can eat about an extra 300 calories (so 2400 to maintain, 2100 to loose). Why only 300? Not totally sure, but I'm becoming convinced that caloric burn calculations are high, at least for me. Whatever my Garmin says I burned, I cut in half and subtract 200 to determine what I can eat over 2100 (remember that calories are energy so starving yourself to death ain't good either - you need to eat enough to be able to workout.)
After you've lost the weight and maintained it for a few months you don't necessarily need to track things in detail all the time but it doesn't hurt to do so for a week or two once a quarter if you feel like you're slipping a belt hole.