Originally Posted by
Random Rider
Trek 7100 Hybrid bike.
Aha, okay -- that makes a difference.
What I mean is, when people say "xx cm", they're usually talking about a road bike frame. I'm 6'2"-ish and have a 60 cm road bike with a slightly shorter stem, for example; somebody 5'10" would be best on a 56 cm-ish frame.
But, I have a mountain bike with a pretty similar geometry to your 7100 (sloping top tube, etc), and its size is... dang, the sticker's gone.. I think it's a 21" frame. BUT!... manufacturers measure their frames a little differently, too, so my Schwinn likely isn't a geometric cousin to your Trek.
So, your 20" bike is a size M on Trek's site --
http://www.trekbikes.com/us/en/bikes...0_series/7100/
Yours
may too big for you. However, for me and my mountain bike, I can hardly reach the ground with both toes while seated... but I'm comfortable, and I can ride for a long time. I fit correctly on that bike. If I'm on a bike that's too small -- which I've done before -- my lower back starts killing me within fifteen minutes.