You can get Rented bike in rishikesh. near bus stand there are lots of shops available from where you can get a rented bike. as you mentioned you wanna go to auli. auli is quite far from rishikesh. it will take around 10 to 12 hours to reach joshimath from rishikesh. start your journey as early as you can in the morning so that you can reach before sunset. . .