I have lived near Austin my whole life but I have never been to Portland. I live in a town just outside of Austin called Pflugerville and haven't been biking for very long. From what I know of Austin it might be scary to bike in the city because of traffic. I recommend taking a 10 min drive to Round Rock or one of the cities nearby and riding there. My mother rides on the roads in Pflugerville and Round Rock and she loves it. There are also lots of sidewalk trails that bikes ride on all the time and its a nice scenic ride. If you are doing more of a mountain bike thing like me then there are more places in Austin to ride, you just have to know where to look. The weather in Austin is very hot and humid in the summer so if you go there make sure you keep water with you.