We have two routes from Delhi to Manali. The best route is via national highway 44, which is the fastest. The distance between the places by this route is 535 kms. You should reach your destination in 13 hours. There are a couple of viewpoints along the way. You can make stops and enjoy nature, and refreshments.
September to November: September is the end of the monsoon season and the winter just sets in. Winters are cold in Manali. The town receives its first snowfall around November last. Do carry some heavy woolen clothes as the temperatures can drop down below zero. December to January is the time when you can enjoy snowfall. This is the ideal time for adventure enthusiasts who want to go skiing. March to June: The summers in Manali are pleasant. The temperatures during these summer months usually vary between 10°C to 25°C. This is the perfect time to indulge in outdoor activities such as paragliding, rafting, trekking and mountain adventures in the Solang Valley. The valley is covered with flowers and is a sight to behold. July-August: Monsoons in Manali are not an ideal time as there is heavy rainfall accompanied by landslides and traffic. However, this is also the time when you can get the best bargains on hotels.
The other route is via the national highway 3. This route passes through the Patiala in Punjab. The distance is around 600 kms and takes about 15 hours to reach Manali from Delhi.
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.