Thousands of bicycle riders in the annual expedition across the state will be hitching a ride home today, or leaving the state till next year’s RAGBRAI. Rider Jon Cook was among those who began last Sunday by dipping a wheel in water from the Missouri river. He explains it’s a custom from the beginning of the 32-year event, though some have amended the final phase of it. You’re leaving the Missouri and heading to the Mississippi where you’ll dip the other tire to symbolize the end of the ride, except for those tired riders who zoom right off the end of the dock into the river. After a ride that’s usually been much hotter than this week, riders are ready for a dip, and bystanders may welcome it, too. Cook says “I imagine there are a good number of bicycles resting at the bottom of the Mississippi,” owned by people who decide after the great ride they could use a new bike — he says they “go screamin’ off the dock,” plunge into the river, and come swimming back to shore.