I'm a pretty big guy and always prefer a smaller frame than what I "should" ride. Probably due to my BMX racing roots. I'm 6'0" and ride a medium. My old Specialized P.3 was a small!
For me, a smaller bike seems more maneuverable, especially in the air.
My old XC bike was a Large and although I fit on it, I always felt too stretched out on it, even with a shorter stem.
Another funny thing is that I can also ride all of my wife's bikes. I ride a 55cm road bike, her's is a 54 cm, so I too only have to raise the seat a "wee" bit. Plus, it helps that women generally have longer legs proportionally to men. That's the case with my wife, she is only 5'6",but has a long inseam. I'm 6'0" with these short stubby legs, and my inseam is only a tad bigger than hers!
When fitting people to mtn bikes, when they're right between sizes, generally I put them on the smaller of the two if they're "actually" planning to ride off-road. This provides better maneuverability and more clearence for "da-boys". If they're "sidewalk cruiser" types, I'll move them to the larger size!
L8R
L8R
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"Life is not a journey to the grave with the intention of arriving safely in a pretty and well preserved body, but rather to skid in broadside, thoroughly used up, totally worn out, and loudly proclaiming, "WOW, What a Ride!" - unknown
"Your Bike Sucks" - Sky Yaeger