After watching the Ken Smith video I noticed he was measuring the width of the front deck right at the seat post. He listed the SDC to be 52" wide. I have taken measurements in the past of my 21XD and thought that seemed a little different than what I measured. I just measured my front deck with the tape touching the seat post and it was right at 56", maybe a little over. That is from inside the cap to inside the cap. Even from the edge of carpet to carpet is 54". Is there a difference in the 2 front decks. Is the 21xd made different than the SDC? could mine have been mounted farther back so its a wider measurement?