How many Calories??

My rule of thumb is 35kcal/mile for 'urban' start-stop cycling, which seems roughly consistent with rates of weight loss vs kcals consumed that I've seen when i've gone all obsessive-compulsive with excell when dieting. Massive amounts of noise in my data there though.
If anyone has any better means of calculating kcals, let me know ..

As it's based mainly on air-resistance it's more difficult to estimate kcals vs distance . I think you largely get the weight vs gravity back on the downhills (a bit less because you're faster downhill?) I've seen tables that estimate it along these lines..

<15mph: approx 20kcal/mile.
15-18mph: approx 30kcal /mile

Quoted message said:

20mph: approx 40kcal /mile

I think it's better to think in terms of time & intensity rather than distance for estimating kcals ?

Your calorie deficit:
25lbs/3weeks = ((25/2.2)kg * (7000kcal/kg))/(3*7 days)
= 3787kcal / day
for me: that would be = approx 108 miles/day .. then again you describe a heavier bike+rider combo + suspension.

still sounds unlikely.. Even if you were burning double per mile thats still 50miles a day. Then again I beleive TDF riders cover 100miles a day in training. (i certainly couldn't !)

I've seen as much as 3kg in 'noise' from one end of the week to the other (weekends of massive binge-drinking nights out -> dehydration etc -> getting back into a fitness regime in the week etc) .. but noise like that evens out when plotted over a period of weeks.