What was it? The extra weight higher up on the machine?
Part of what I like about the Zero's is how light, balanced and nimble they feel compared to an equivalent powered ICE bike. Adding the Power Tank reduced that. Getting my DSR+PT off its side stand took as much effort as with my 650 lb touring bike. Negotiating at parking lots speeds required some really heavy-footed dabbing if it started tipping over.
Once at speed, it wasn't as noticeable. You could feel it in fast corners kind of wanting to fall in on you, but was controllable. The other big issue was degraded performance. It slowed the acceleration of the bike down enough to notice it. Based on what others have said, the placement of the PT might have contributed some of my overheating issues, not sure on that.
The SR/F is already around 500 lbs. if I remember correctly. Adding a 45 lb PT to it would push it up in 545 lb range. That's pretty heavy for a street fighter type bike. My Speed Triple is about 100 lbs. lighter than that and its not one of the lighter ones in the class.