Does the soft roof pad need to be longer than the board?

[BaNZ]

I'm choosing between a 18' or 28' Dakine aero rack pads. A long board is usually around 22' so it will be bigger than the 18' pad. I don't see that a problem but wondering if I should spend a little more to get the 28'. However 28' is an odd one because it is most likely not long enough to have two boards side by side. I usually just stack two boards on top of each other.

[BoMan]

IMHO the 28 inch pads are worth the 10 extra dollars to protect your roof when the load shifts.

[waikikikichan]

You ever seen board storage racks, either vertical or horizontal ? The arms that stick out don't need to be as wide as the board. So as they're about 3/4 of the way. Just like the rocker doesn't allow the nose and tail to touch the ground, when laid on it's belly, so does the dome of the bottom from rail to rail basically only allows the middle area to touch, you don't need to support all the way out to the rail. 18 inch is fine for most longboards. 28" is for those 29"- 34" SUP's.