Well, I ended up buying the Bridgestone S21's for my bike. And I got the 190/55 for the rear. The reason for my purchase? The tire had great reviews, and after the mail-in rebate, the set cost me $180 delivered to my front door! I have only put about 60 miles on them, but they feel great, and the 190/55 rear makes it feel 100 pounds lighter! Will keep you posted

I totally agree on the feeling of weight loss. I just went with angel gt's myself in the 190/55. PS. where did you score that deal on the s21? I would consider buying some now for next years use at that price.

Through Rocky Mountain Cycle online. They were $230 for the set and had a $50 mail in rebate

^^^ I've bought from them b/c of the good deals... another good online shop is motorcyclegear.com..they tend to have some insane deals.

next time go with 200/55 for even better turn-in response

I would be really interested in a long(er) term review in the future? There is some discussion on a different forum that after break-in due to the torque monster tearing up the material under normal zx14 acceleration (meaning very hard) the straight line stability gets squirrely.

I would also be interested. Previous bike I ran Dunlop Q3's...broke in fast and stable as anything!!! But they did wear fast. Just checked with my local guy and the Ninja's Q3 are a bit more than the S21's....
Let us know how they hold up!!!

I had a set of S20 Evos and they were OK. Muddy feeling feedback and down right scary at the end of their run. There OK tires but there are just better. It'd take quite a bit for me to try Bridgestones again.

I had the Slipstones S20 on the BBW when she was new, no issues at all and did 2 track days also. At about 3500 swapped them out for Mich PP 2CT with a 190/55 rear and so far so good, I like the Mich PP 2CTs but only about 2800 on them so far. Word on the S21 is that they are good until they aren't then they are unstable. I was only interested because of the 200/55 rear option. Guess when its time I'll stack some cheese and go the big $$$ Pirelli super duper rosso corsa bada bings in the 200/55. Gotta know what all the hypes is about and if its worth 2x for a set of tires.

I've had the S20 evo's (190/50) and the S21's (200/55). Both lasted close over 10,000 with both commuting and very spirited rides. My summer commute includes a combination of highway, back roads and twisty mountain track. Winter up here is cold and wet with mostly highway.

I can say the S21's are far and above a better tire than the S20's but the slipping mention frequently on the 20's was not as extreme as some indicate. For me at least. I imagine pressures and riding style would vary this a lot.

The S20's slipping was more of a "step out" and grab imho. Almost like the sidewall would collapse then rebound. Now I know this wasn't the case but it was unnerving even if predictable. During cold and wet rides this step out was less pronounced but of course this was due to less speed and lean. They did heat up well however and kept their heat.

The S21's, for me at least, was the tits. They were very predictable and grabbed far better than they had a right to. The front felt like the bike was chained down and I could ride it's edge all day without fade no matter what the temperature. The higher profile allowed quicker turn in but they produced zero fall into corners. Just even roll out to the edges. Cold and rain were not an issue as these too would heat up fast and keep the heat soak going when stopped for a while. One negative I will mention and everyone can evaluate if it is in fact a negative, would be a definitive transition between compounds in the rear when leaning hard. Nothing abrupt but there none the less. The front displayed none of these symptoms. Maybe due to the three compound as opposed five compound of the rear.

In the end I wouldn't hesitate to recommend the S21's and given their similar price to the S20's I'd say skip to the 21's without question and enjoy. Hope this helps someone.