Is there a design/functional purpose for the extra wide doorsill in the XJ? It seems to me that the extra inches could have been used for a bigger interior. Basically the XJ is a large sedan with a compact interior and a cramped footwell. The big doorsill is also an injury hazard for hitting your foot or ankle. What was Ian Callum thinking??

 

I've wondered about the same thing. However, from a side impact resistance viewpoint I think it is a favorable design element.

 

Due to the all aluminum design, this is a downside to that architecture. You need the depth (side to side wise) for any accident occurring to the side of the vehicle. In the name of having the "safest vehicle in the class", something has to give.

 

I am guessing if you pop a sill off and peak under the carpeting, you will find the wide lip is for electrical harness runs and for very thick foam (sound deadening). At least that is the case with my X350 - the foam is at least an inch thick.

 

A doubling of side thickness cubes the resistance to bending under impact. Of course that doesn't console my wife who bangs her ankles getting in or out.