We have been able to start on some relatively steep pitches 15-18% grade (on dirt) on our MTB tandem in a low gear of 22/36. At times I have had to rely on my wife to power us through while my leg gets spun around as I'm trying to get on the saddle. Our biggest issue is being in a spot where the dirt is not too loose and keeping traction with the rear wheel. If we do spin out I need to get my foot down FAST!