Mountain bike vs. road bike question...?

I signed up for a 100 mile bike ride this past weekend and was only able to do the 62.5 mile course. I was literally the only person there with a mountain bike and everyone else had a road bike. It took me 7 hours and the entire riding time allowed was 9 hours, so I couldn't have done the 100 automatically.... show more I signed up for a 100 mile bike ride this past weekend and was only able to do the 62.5 mile course. I was literally the only person there with a mountain bike and everyone else had a road bike. It took me 7 hours and the entire riding time allowed was 9 hours, so I couldn't have done the 100 automatically. Some friends have said a road bike would have made a huge difference. I'm in decent shape and people in much worse shape were blowing by me on their bikes. Can someone explain this to me? Were my friends right about road bikes?
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