Not sure if this has been discussed before as I'm new to an ST1100 and new to the forum. The standard seat is quite slippery for the pillion so, I bought some rubber drawer liner from Crazy Clarks at $2 for a roll. Wrap this around the pillion seat and underneath. The wife now doesn't slide and it hasn't ridden up or creased in three rides. It's a lot cheaper than aftermarket, purpose built items (like a Triboseat cover) and doesn't look cheap. It looks like a part of the bike.