Nope, not on a tandem although I stick to his wheel so we might as well be on a tandem. He is a very strong rider and pulled a group of us at around 24 mph the first 100. He simply did not drink enough water and take enough electrolytes throughout the day and it finally caught up with him. It was really scary and I didn't know if he would be able to shake it off. We stopped about 20 miles before we got to Portland and got him something cold to drink and threw some electrolytes down him and then I pulled for a while and he slowly came back around. Poor guy was even too sick at the end to finish his beer in the beer garden. That is when I knew he was feeling bad!!! Being the good wife I am, I finished his beer for him