What can a beginner biker riding a 21 gear mountain bike ?

Question

what is a good gear to start training and what speed to avg for

Answer 1

It has 21 speeds for a reason. You change gears depending on the level of the road you're on.

Answer 2

You want the gear that you can  pedal at a cadence of 70-90 rpm's  If you start to slow down shift to a lower gear, too easy shift to a higher one.

Answer 3

there isn't one gear that you should train in, that's ridiculous. I'm gonna enter a race (sea otter classic) and I usually shoot for 12 mph average on over 8 miles with a lot of hills.

Answer 4

i don't know much about mountain biking, but for road riding, rpm is more important than speed.  you should try to maintain the same rpm no matter if riding uphill or flat. so change gears often so your legs won't get as tired.

once you've mastered rpm, the speed increase will come naturally.