We were somewhere around Moreton on the edge of Epping Forest when Huey Lewis and the News took hold. A group of riders behind me had mounted speakers and were singing along, "You don't need money. It don't take fame. Don't need no credit card to ride this train," and then groups coming up, passing me, doing a kind of seated shoulder groove on their bikes, belting it out, "It's strong and it's sudden and it's cruel sometimes." God help me, I joined in. "That's the poooower of love."

We were about 20 miles into the Dunwich Dynamo, a rock-up-and-go, 120 mile night ride out of Hackney, through Epping Forest, across Essex and the Suffolk Prairies, finally down to the windy, beach at the lost city of Dunwich. It's proudly "semi-organised", with Southwark Cyclists getting us and our bikes back to London by coach. The London School of Cycling handles the route and offers this helpful advice on the route card: "Pretending you're in a road-race on a touring event makes you look like a DUFUS". (Emphasis in the original.) There's not much help beyond that, certainly no support van or mechanics. It's just you, your bike, and 2,000 like-minded individuals pedalling through the night.

There's the fun of cycling at night in an endless, twisting snake of twinkling red and white lights, but what makes this ride are the riders. You see all forms of life: lone racers with bananas taped to their top tubes, club riders speeding by in matching kit, MAMILS, college students out for a laugh, little teams of Italians and Spaniards, dudes on fixies, couples laughing on tandems, long haul tourists with camping kit, recumbent cyclists, tattooed messengers types, and at least one older gent in shorts, a linen shirt and deck shoes, making good time. You fall into groups, and there's a kind of quick bond formed by the shared hardships of a long ride.

A particularly well-lit team of riders – they looked like bioluminescent things from the deep sea – caught me up and asked how I was doing. "Yeah, I'm good mate" is all anyone ever said until we were near the 90 mile mark and felt complaining was finally legitimate. It was their third "Dun Run" together. A lot of the people I talked to had done it before, but there was a real feeling that many more newcomers were about this time. The landlord in one of the pubs staying open late for us complained, "Seriously. Who orders coffee in a pub? Used to be pints of Guinness. What's this world coming to?" A cyclist ordered two pints of Guinness. "There. See? Good man! Well done!"

As the night wore on, the party atmosphere changed. Past one in the morning people ran out of small talk, and some conversations got serious. Two ahead were talking about first loves. "She was from New Zealand. When we split up I could still smell her hair on my hands. It was like holding flowers. I didn't wash my hands for two weeks." But the more progress we made, the more focused everyone was on getting to the end. Laying by the side of the road, feeling near death and slurping a gel in a damp sleeping hotspot, every conversation all around me was about the end.

Once I made it to the beach, drinking beer, watching a few swimmers brave the angry waves, I sat with Charlie and his mate, fast asleep on the pebbles, whoever he was. It was all about numbers for Charlie. "At mile 40 I thought, OK, that's a third, might not make it, but since mile 70 it's doable, right? At 60 I thought, no way, distant prospect, 60 more miles, been a long way and a long way to go, but at 70 you're like, only 50 more right? And then at 80 it's like, only 40, I can do that." I asked if he was up for it again next year. He and his sleeping mate said, in perfect unison, "Definitely."