Outside some of the more popular guesthouses and hotels you may find private vehicles with driver for hire. Rates can be very reasonable. Negotiate the fare before departure and don’t forget to ask whether fuel is included.
Same rules apply as hiring a motorbike. Check the car thoroughly and study the insurance which comes with it. A good searching ground for motorbike and car hire is along the Moonmuang Rd by the moat there are a lot of places here offering a good variety of cars. There is also a branch of Budget Car Hire in town.
You can also hire a car in Bangkok or elsewhere for getting to Chiang Mai, and drive up at your own leisure, stopping off in Ayutthaya and Sukothai. The countryside is quite pretty as you enter the mountains from Tak or Phitsanulok onwards. With dual-lane highways most the way, reaching Chiang Mai by car is a straight-forward journey of about seven hours. Driving in Thailand is on the left hand side, roads are in good condition but driving habits here are typically poor and accidents common, so drive defensively.