a high butt/short back tend to feel pain at two points, the bony ends of the lower rear section of the pelvis known as the ischium. This double bunache also results from poor riding posture, when your weight is carried forward over the saddle. Low butts, and those who sit back or bolt upright, seem to get a centered ache since the coccyx (what's left of our discarded tail) grinds into the seat. The nerve pain some riders encounter down the back of the left leg, is the result of coccyx-supported posture. The pressure is transferred to the lowermost vertebrae which, in turn, pinches the sciatic nerve. The ergonomics of the motorcycle also bear on how you sit on the motorcycle. Motorcycles with their footpegs set rearward cause more of the rider's weight to be taken on by the legs. If you lean forward on the handlebar, more of your weight falls on your hands, arms and shoulders. Cruisers, especially those with fottpegs set up near the front of the engine, put most of the rider's weight squarely on the seat.