What is the maximum possible, load a typical 18 wheeler can carry

That is a perfect answer. 105,500 lbs is the max. and as long as you don't go over the max weight per axle of 20,000 lbs and the axles are spread far more than 8-10 feet apart you can accomplish it and with the right over weight permit. But not in every state.

 

The steering axle, however, must go by the load limit by the tire manufacturer.
The max the steers can be is 20,000 lbs. but most steer tires have a max load of 6,175 lbs per tire, allowing 12,350 lbs on the steers. But some larger sleeper trucks have a higher tire rating that will allow up to 7,160 lbs per steer tire and allowing 14,320 lbs on the steers.

 

Something to do with maximum size too?