How to estimate calorie intake requirements for bike

The answer you seek is somewhat individualistic - gotta find what works for you (which will change based on a number of factors including beginning energy stores, temps, effort levels, race duration etc.). Many of the manufacturers of nutrition products have calculators on their websites. Might start there.

I've been fiddlin' with the same issue and have been working off a target of 350 cal/hour in the form of "solid" and drink (as part of the hydration need). Just to illustrate my point of this number changing based on conditions, the 350 amount worked well for a century early this summer (mostly flat, medium effort level, cooler temps, little wind) and failed miserably today (slightly longer ride, but hilly, windy and hot).

Hey, next time you're out riddin' swing by my folks house and say "hi" - they live in Fayetteville. Good luck on your upcoming ride.

Step #1 Determine your goal cycling speed
Step #2 Multiply cycling speed coefficient (see table 1) by your total body weight.
Step #3 Multiply Step #2 by 60 minutes to determine hourly calorie expenditure.
Step #4 Add 22 calories to Step #3 for every 100 feet climbed during cycling event.
Step #5 Multiply Step #4 by 0.3 to determine minimum hourly calorie replacement demands
Step #6 Multiply Step #4 by 0.5 to determine maximum hourly calorie replacement demands

Table 1. Calculating Calorie Expenditure during Cycle WorkoutsAverage Speed (mph)

Coefficient (cal./lb./min.)*
15 0.0561
16 0.0615
17 0.0675
18 0.0740
19 0.0811
20 0.0891
21 0.0975
23 0.1173
25 0.1411

But then so does the one on the Infinit site: lean muscle mass x 2. But that one is a lot easier.

I had already worked out something by trial and error and these formulas were right in the ballpark of what I had worked out. But YMMV.