Hi Mapsito,
Welcome to the bike hub. Starting an exercise journey is a big step for most people and from the weight and height stats you provide I imagine that this step is a significant one for you too. You don't specifically state that weight loss is a goal but many of us do come to this sport for that purpose. I am assuming this is the case for you too.
What joemerida says is true - a total system mass of 170 plus kg is outside the spec of any bike I've seen. I am not an expert but I think the biggest issue might be wheel strength. So basically getting on most bikes, with the possible exception of a titanium framed bike, is not really going to work for you at this stage.
On the up side, cycling is a great sport for us heavier okes because it doesn't stress knees and other joints as much a higher impact activities like walking and running.
That having been said, it might be worth starting with some brisk walking 3 times a week for 20 minutes at a time just to begin the process of burning more calories and getting your cardio vascular system a little more tuned.
It may also be worth getting a GP's go ahead before starting - you don't give your age but at your body mass index (BMI), stressing the heart with an exercise programme is a risk factor.
I would say once you hit the 140kg mark, the bicycle would become a more viable form of exercise. If you have access to a gym, a more robust stationery bike might also be a good way to get the legs spinning.
Every strength - there are lots of people here who have used the bicycle to transform their bodies and once the bike bug bites, you're generally hooked for life
