How to reach climbing weight:
Step 1. Learn as much as you can, from websites like
www.bodybuilding.com and
www.t-nation.com about the physiologic effects macronutrients (carbs, fat, protein) have on the body. Learn about when you need fuel, when you dont, what you need to repair, etc.
Step 2. Create a caloric defecit. Luckily we ride bikes here, so its kind of easy for us. Go out and ride on an empty stomach. Yes it will suck, yes you'll go slow, yes you will be pushing yourself, and yes, it works. Theoretically, doing this can train your body to turn fat into usable energy easier, especially if you do intervals on an empty stomach. Intervals build mitochondria in your muscles, and with glycogen low the new mitochondria will adapt to using fat, thus your ratio of total fuel usage will shift a little bit. In theory, you will be able to burn fat easier in the long run. It is a theory, but I believe it to be true based off of my personal experience.
Step 3. Body Composition, in my opinion, is more important than just weight with regards to climbing. I've been 130 and muscle-less and terrible at everything on a bike. I've been 145 and rather average at everything on a bike. Right now I'm around 135, lean, but I have a really strong core and muscle on my frame and my biking is good. So dont just try and lose weight and only do that, you'll go nowhere and everything will become hard.