Bought a road bike 2 months ago , lost nearly a stone with no diet change. Take saturday for instance up at 7 am grab odds and sods bike out of garage away at 7-30 , home for 1 ,oil chain put bike away, 70+ miles taking in Hardknott and Wrynose brew in Coniston.
Typical previous Saturday up at 7 ,load up car get gear out for 8 , drive 45 mins off load all gear put bike shoes on coat etc , its now 9 am, ride 2.5 hours load up bike get changed set off get home £20 diesel used ,off load kit nearly 1 oclock and stood facing an hour clean down, which i will do tomorrow! So with no extra time i have doubled my pedalling time and when it comes to the big hills on the road full on effort can get me over everything, come to mtb and a steep technical climb might beat me technically rather than lung busting so end up pushing not for fitness reasons.Have mtb for 8+ years twice a week with weight staying pretty constant,now I may add one or two evening hour blasts in on the road bike that I would not do on the mtb due to the ease of road. Went out mtb last week felt alot fitter. So only in my opinion a road bike does improve fitness, and the mrs can`t get enough of me in the bib shorts with my kite sticking out, Not!!!!