"My last board was a 156, and I liked it, so tell me about the 156's that you carry." The trick here, is that two boards of identical length, may be designed for completely different riders and types of riding. For example a 156 may be a "big mountain board" for a small rider, or a "park" board for a big guy, depending on the manufacturer's design plan. Those two boards, however, would never be appropriate for the same rider.
Length is often discussed in terms of: longer equals faster, and more stable, while shorter equals more maneuverable. This can also be deceptive. The "running surface" of a board (the base area that contacts the snow) is a useful measurement, because this is the amount of board that you actually are riding upon. The overall length (the measurement usually considered) can be misleading, as it also contains the raised tip and tail, which do not contact the snow, and have only nuance differences in affecting your ride.
Your best bet is research. Look into who the board was made for, and for what type of riding. Leave the rules of thumb to the rental guys, who are trying to get through the line of renters as quickly as possible, and get on the slopes (can't blame 'em for that).
Board sizing has always been a little tricky, but in the past, there have been a small group of readily available stats that have been very useful for comparison and selection by knowledgeable riders. One of those has been Running Length (AKA Contact Length). As we have written many times, overall board length is a commonly considered, but almost useless measurement. Why? Because the shape and dimensions of a board's raised tip and tail can vary greatly and have next to no impact on the way the board will ride.
These variations may change the overall board length by as much as 7 cm without having any significant effect on performance. I can feel some readers out there bristling to say, "but length effects spin weight and rotation". Sure, but in reality the difference in weight is negligible, and the difference you feel in spins is minor at best...and, most importantly for this article, tip to tip length will always be provided, so if it is important to you, it will always be available.
Most informed boarders have paid little to no attention to overall (tip to tip) length but have focused on Running Length as a major indicator of a board's true "size". This measurement was highly valued as it gauged the amount of board that would be in firm contact with the snow while riding. The running length was typically taken as a straight line measurement between the two contact points, which on traditional cambered boards pretty well corresponded with the board's wide points at both ends of it's effective edge. So, this really became a wide point to wide point measurement. Some manufacturers would measure this with the camber compressed (weighted) while others would take a non compressed measurement. In either case, the numbers were pretty close. Good retailers kept their own consistent internal measurements.
Enter Rocker. Rocker is an often incorrectly used term that inaccurately groups about twenty different variations on Reverse Camber designs. One confusing factor that stems from the addition of "Rocker" boards is that due to the design of many of theseshapes, the tip and tail, when weighted, are not in contact with the snow. So, how is running length being measured for Rockered boards? Well, that's interesting. For the mostpart, it's no longer being measured at all. Manufacturers that have been providing this measurement for years and in some cases decades, are now excluding the measurement from their literature and websites. Others have simply continued to measure wide point to widepoint, even while this is no longer a true representation of contact length.
Our suggestion: Two separate measurements. The fist being true weighted contact length and the second being the wide spot to wide spot measurement. This will allow the knowledgeable board seeker to get an idea of real running length, plus "available" running length (available by selective pressuring, even if not all at once) and wide spot distance to better gauge where the potential catch spots are in relation to rider stance. But at least for now, Running Length, R.I.P.