With the latest generation of Super Singles, the needs of the vast majority of the US loads on the road today can be met without the drawbacks of the old 1980s' design.   Two major design improvements are smaller size and higher capacities (up to 22,000 lbs). The diameter is the same as that of low profile, 22.5 inch radials (ie. 295/70R22.5). While this similarity can result in no clearance problems when fitting them onto an existing chassis / trailer, the conversion is not so simple.  A different type of axle and components may be needed for the conversion.  

Weight Reduction:

125 lbs when replacing a set of 2 Conventional tires / Steel Wheels

60 lbs when replacing a set of 2 Conventional tires / Aluminum Wheels

Fuel Savings:

Since you have half as many tires (sidewalls flexing), you should see a 2-5% increase in fuel economy depending on the adoption at both the tractor and trailer wheel position. Sidewall flex is directly proportional to rolling resistance.

Blown Tire:

When a Super Single tire blows, you will now it according to truck drivers. The only place you can go is the side of the road because there's no other tire next to it to help you limp to a truck stop or a tire facility. Furthermore, when a blow out does occur, the cost to replace one wide base tire versus one half of a dual set up is increased.  Not to mention that the closest dealer or truck stop aren't going to be as well-stocked with wide singles a with conventional tires. 

Spread Axle Applicability:

Fleets have found that excess tire wear due to "scrub" from turning does not make wide base tires acceptable on spread axle chassis / trailers from a cost standpoint.

Higher Initial Investment:

Super singles is considered an upgrade by chassis / trailer manufacturers.  Hence, the chassis cost will go up considerably.

Needless to say, the call is yours !!