Well they say a fit smoker is 6 times more fitter than a non fit smoker on the same level training. Im a smoker, when I cycle a 120-150ks i take my cigarettes with. When I come back from a 20k run i light up my cigarette. At first it was a shock on the lungs. As training went by, the lungs got used to it. Smoking and hill riding. If you are used to it, you will be fine.