Can you buy a larger bolt on tank for the sportster?, and I do mean bolt on.

 

Look at custom chrome and I think Drag Specialties. also try an Ebay search for fat bob.

not sure what style your looking for though.

 

I've got a 'Drag Specialties Quick-Bob' tank on mine.

 

You didn't say what model sporty that you have, but if you have the 3.3 gallon tank, you can upgrade to the 4.5 gallon tank that comes stock on the custom with an adapter kit to make it fit. I'm in the process of upgrading my roadster that had the 3.3 gallon, but also be aware that you will have to change out the seat as well because the 4.5 gallon tank is a couple of inches longer than the 3.3. Purchase of this tank will run you about $400-550 dollars depending on if you buy direct from harley or go with an independant (still oem from harley only cheaper). The adapter kit is about $20 or 25 bucks as well. I went with a mustang wide vintage seat for comfort and it runs about $400 bucks for the two piece set-up. Should have my bike set up in a couple of weeks due to mustang seat is on backorder. will post pics at that time. Later.....