What tool is used to shave seat foam to make a seat lower. A sharp knife and then use an abrasive to smooth it out? My son (vertically challenged, 12 years old) has a hard time one legging a full size bike but is determined he is going to ride a full size bike. We are not in the bike selection phase, we are committed to a full size bike(KX125). We are also considering lowering the sub frame mount to lower the seat height also. I know there are mostly large folks riding the BRB... But has anyone seen or heard how this is done?