I broke the derailleur cable on my MTB, and only had one front sprocket at the time (bam! singlespeed). Unfortunately, I was on site for a ride with some friends who had never ridden offroad before, and they were desperate for some morale-boosting companionship. So I rode 32x28 for 2 hours. Wasn't toooooo bad since they were so slow, and I could still coast downhill. But pretty bad.