I have a city or normal bike and I want to ask, that with the necessary modification except the frame, is possible to convert this bike in a road bike?
1This question has come up multiple times - have a brows of the site and see the existing good answers. Basically unless you have a lot of spare parts (ie a donor bike) its too expensive.– Criggie ♦Jul 27, 2018 at 3:49
1Apart from frame geometry, road bikes differ from city bikes in a) handle bars and b) wheels. Of course, you may try to adapt either of these two. Replacing handle bars may produce geometric problems (handle bars collide with upper tube and such), replacing tires/rims should be relatively straight forward and will definitely reduce rolling resistance. Still, your frame will remain heavy.– cmaster - reinstate monicaJul 28, 2018 at 8:41
Depends what you mean by city bike and road bike.
If you mean converting a bike with flat bars to one with drop bars there are issues. Flat bar bike frames are typically longer than drop bar frames, because flat bars place the rider's hands closer to the head-tube than drop bar hoods or drops hand positions do. Also, compatibility of brakes, levers/shifters and derailleurs can be problematic.
It is very likely you would end up replacing a significant fraction of the components on the bike, and it would be more cost effective to sell it and buy the bike you want.