Padded cycling shorts are a must for a long ride. If you don't routinely do 20 mile or longer rides, your crotch will hurt like hell if you wear regular street clothes, such as baggy shorts, and do 40 miles.
I was injured this past December and January and was grounded. A friend and I had signed up for the February 9th 55 mile TOUR DE PALM SPRINGS bike ride before the injury. I didn't want to cop out, so I did the ride with no training for the 2 months before the event. Normally, 50 mile rides are no big deal. Even with the padded cycling shorts, my crotch was sore by mile 30. It hurt for 2 days.
Do yourself a favor: Get a pair of padded cycling shorts if you're going to do this ride. Remember to lube your chain and pump up your tires. Good luck!