Chiang Mai residents who don't have their own wheels rely on the ubiquitous rót daang (literally 'red truck' or sŏrng·tăa·ou) or túk-túk.
Rót daang are shared taxis: you can flag them down, tell them your destination and if they are going that way they'll nod (ever so slightly). Along the way they might pick up other passengers if the stops are en route or close by. Short trips should cost 20B per person (eg around the old city) and longer trips from 40B per person (eg from the old city to Th Nimmanhaemin), and more depending on the distance and your negotiation skills. If you travel from the riverside area to Th Nimmahaemin you'll probably have to pay around 40B. By and large you shouldn't have a problem with rót daang drivers being too greedy about fares. Most quote honest prices and it seems to be something of a tradition for the drivers to scoot around town in the evenings and on weekends with their wives in the front seat for company. If a rót daang is parked alongside the road, the driver prefers to charter the vehicle for trips to attractions, such as Doi Suthep, or to tourist attractions that pay a commission (animal shows, San Kamphaeng etc) instead of running a shared taxi route.
Túk-túk work only on a charter basis and are more expensive than rót daang. Rates start at 60B to 80B for most trips and creep up to 100B at night when people are returning home from the bars. The benefit of túk-túk is that it takes you directly to your destination and the driver usually speaks passable English. The drawback is that the drivers can be a little more aggressive about fares and prefer to steer their customers to attractions that pay commissions. Regardless, this is the best option for trips to/from the bus station, train station and airport when you're burdened with baggage and don't know your way around.
Chiang Mai still has a few săhm·lór (pedicabs), typically parked at Talat Warorot. Săhm·lór cost around 20B to 30B for short trips near the market.
Túk túks are more expensive and their drivers are likely to rip you off, but they do offer a direct service and most drivers speak English. Sŏrng·tăa·ou drivers are cheaper, less inclined to rip off passengers (because many Thais use them too), but English can be a problem and routes are not always direct. Riding in a sŏrng·tăa·ou is an excellent way to meet local Thais.
Private transport is available from rental agencies throughout the city, mainly along Th Moon Muang. Be sure that the vehicle you rent has insurance (liability) coverage, which usually includes a 5000B excess. This does not cover personal injury and medical payments of anyone injured in a traffic accident. Ask to take a look at the terms of the insurance policy so you're clear on what is and isn't included. Standard rental rates for small 1.5L cars, such as Toyota Vios or Honda Jazz, start at 1500B. Weekly and monthly rates are available and petrol is not included in the price. Unlimited kilometres should be included.
One of the most well-regarded agencies is North Wheels, which offers hotel pick-up and delivery, 24-hour emergency road service, and comprehensive insurance. Another good bet is Thai Rent a Car, located at the airport. Other car-rental agencies in town include Budget Car Rental, across from Central Airport Plaza.