What everyone else said about not worrying about it, especially if you're losing inches and becoming firmer.

But I will say this: for me, when I'm running more than I'm riding, I will gain weight. Simple reason is that it's just more intense and I can't sustain it as long. Even now that I'm doing one four- or five-hour run each week, that's way different from three or four six-hour rides each week at a lower intensity.

So if you're running more and riding less, take a look at your total expenditure.