The minimum insertion line for all Thudbuster models is 100mm, that means you MUST have at least 100mm or more of seatpost that is inside of your bicycle's frame. 

    For the NEW Thudbuster LT, the maximum extension (the highest it will protrude from the bicycle frame) will be 320mm for the 30.9mm and 31.6mm options, and 290mm for the 27.2mm Thudbuster LT.

    For older generation Thudbuster LT's (3G), The maximum extension will be 300mm.