I've lost 25 lbs in 16 weeks- how and why?

In October I decided that I was too heavy for the types of races that I cared the most about.  I felt I had ridden well all year and particularly well in the late fall, but realized that it was probably in spite of my 193 lbs.  It seemed obvious that in order to compete at a higher level I would have to find a way to lose a significant amount of weight, and to do so without losing too much power.

I wasn't sure how much weight loss to shoot for.  When I was a ski racer I always struggled with being too light and was always trying to gain pounds in order to take advantage of gravity a little bit more.  My experience thus far as a cyclist didn't give me a ton of insight-  I have steadily improved year to year despite my weight fluctuating from about 170-190 seemingly randomly.  I initially figured I needed to get down to at least 180 or that range (the weight I had been at for the Royal 162, Keeweenaw Chain Drive, etc. part of this year).

My plan to lose the weight was simple-  stop drinking more than 2 servings of alchohol on any given day, skip bedtime snacks...

I lost 8 lbs between winning the Dirt Bag and the Midwest Championships CX races.  At the Midwest Championships I rode strong and technically well, but the fast Juniors I was up against were generally able to drop me on the toughest climb.  I started thinking about how much better than 6th I could have been if I could keep my strength, skills and be as "light" as the kids.  I looked at my body and considered how much of that weight really was wasted fat (I certainly had some extra "belly").

I set new goals-  175 lbs by Triple D, 170 lbs by CIRREM, 165 at Ragnarok.  I knew I would have to work to acheive those goals and that the biggest danger would be to lose strength and/or risk getting sick if I didn't get proper nourishment.  I decided that I would chart my calories using a phone application and that I would make a point of not being very strict about what I ate when I was riding a lot.  I would also use my powertap to monitor my strength as much as possible and to reassess as I went.  I felt like I might be losing my mind, but I decided to try it.

The first few days of actually keeping track of what I ate were very hard.  I felt a bit dizzy at the end of the night at work and was positively starving by the time I went to bed.  I had a few setbacks where I over ate because of trying so hard not to eat too much.  There was even one night where I bonked so bad  between work and home that I had to stop, eat McDonalds and call for a ride.  I was only eating 300-350 calories less than I was burning per day and it felt like hell.  At this point my goals seemed impossible, surely feeling this hungry would mean that I'd get weaker.

After roughly one month of real work things became a lot easier.  I began to find that I was only hungry for approximately the amount of food that I "should" have been consuming.  I had already lost another 7 lbs or so and now the weight was coming off without much additional effort.  I was also solidly in my long, slow, endurance training time of year and riding my bike 9-18 hours a week.  I made my goal weight for Triple D and won the race.  I figure that was somewhat of a sign that I wasn't going totally in the wrong direction.

Since Triple D I've been deliberately eating a bit more-  only shooting to "under eat" by 200 calories or so per day.  However, I've found that I continue to shed pounds at roughly same rate.  I may be underestimating the calories burned while cycling.  I know I'm not burning as many as my Garmin 705 says or that the calorie program on my phone states are burned at various speeds on a bicycle.  If those programs were right I'd have died back in January...   so I estimate based on my RPE and usually "give" myself between 350 and 500 calories per hour.  How do you estimate those numbers accurately? We've had a very warm winter and I've been able to ride my Giant outside with the powertap and do some testing.  I have yet to see any evidence of losing sustained power.  My maximum sustained output for 30 minutes has gone up significantly since I last tested (my speed over the same has gone down-  but it's not very comparable due to 700x30s on my bike in winter, the cold etc.).  I'm actually 167 or 168 now and ahead of my goal weight for CIRREM.

Overall, I'm pretty shocked at how easy losing that much weight has actually been and surprised that, other than being 25 lbs lighter, it doesn't seem to have had much effect on how I feel riding.  It's as if all I had to do was get the ball rolling in the right direction and the momentum is just pulling me along now.
Almost to the point where now I would have to work to reverse things...  over the last couple weeks I've really not eaten "carefully" and I've had a lot of stuff that would definitely not be allowed in any diet, but still when I jump on the scale monday morning I'm down another 1.x pounds.

Time will tell how it ultimately effects my riding.  It's hard to know at what weight I might start to lose my strongest sprinting or at what weight I would climb the best etc. etc..  The races I care about most right now are the Royal 162, Keeweenaw Chain Drive and the Chequamegon 100 (metric version).  I'm convinced that erring on the "light" side would be best for all of those.  That said, at this point I've reassessed and plan to focus on eating healthy but plenty.  I don't think I'll have much trouble with 165 for the Ragnarok and I'm not so sure that isn't an ideal number for me overall.