We have two routes from Shimla to Chandigarh. The best route is via national highway 5, which is the fastest. The distance between the places by this route is 113 kms. You should reach your destination in 4 hours. You can make a stop or overnight stay at Kasauli.
The best season to visit Chandigarh is autumn, i.e., from mid-August to November, when the weather is neither very warm nor cold. It is a pleasant and favorable for a city tour. Winters, i.e. November to February are extreme in Chandigarh as thick fog settles in the air, and the temperature goes down to sub-zero level. However, it is also season for the much awaited Chandigarh carnival held every year in the month of November. Another festival in the winter season is the Festival of Gardens held in February. This festival is a three-day event which is filled with various dances, music and various other activities that highlight the cities culture. During the summers i.e., from mid-March to June months, the heat is scorching as the temperature rises above the 40 degrees C. Monsoon showers do bring some relief in the month of July, bringing down the temperatures though the humidity levels remain high.
The other route is via Kunihar - Ghanahatti. This route is about 115 kms and takes roughly about 4 hours.
The roads like any other mountain terrain are steep and full of curves. However, with professional cab services there is nothing to worry about. Book a cab and enjoy your road trip.