What I keep having to remind myself with these tyres are that they are made for the road, but have the capability for the odd track day. 10 years ago we could only dream of being able to nip down the road and buy tyres this good.
The technology in these tyres has come directly from Moto GP. If you carefully look at the image of the tyre (on the right), you can just about see the three different compounds that keep you rubber side down.
In the centre of the tyre you have a hard (ish) compound, then you have a medium compound, and finally soft on the edge for maximum grip at lean.
Bridgestone's are known for being stable tyres that give confidence due to them having a "slow turn in". I would agree with this. The steering can be quickened up by using a 190/55 rather than a 190/50.
The extra side wall height gives a more rounded profile and gives a bigger contact patch whilst on the edge of the tyre. I'm tempted to go with a 55 tyre next, you just have to be careful of clearance to the swingarm and a hugger if you have one fitted. I've noticed my hugger is getting a hammering as the rubber rolls off the edge of the tyre, and that's with a 50.
I've used S21's on the road and as a pure track tyre, and I'm a huge fan of them in both disciplines.
On the road I've used them on a CBR600 and 1000RR Fireblade. On the 600 they grip like jam on carpet, they do on the Fireblade but you know on the blade when the rears about to let go. On the track this is less so, and I can only put this down to the tyre having a higher constant operating temperature so the rear only lets go if you're early on the throttle out of bends.
They also perform fantastically in the wet. I remember coming back from the TT early in the morning with a bike loaded with a weeks worth of camping kit, and in moderate rain I knew exactly what was happening underneath me.
On the track these have been amazing for "getting into the scene". They work with tyre warmers and within 5 laps from brand new they were already allowing knee down fun.
The only downside I've found with these for the track (and remember these are road tyres...) is that when they get really hot and you give them a hard time lap after lap, the rear starts to break away, spin up and then slide. But, its very predictable, and I'm no hero by a long stretch but you can keep the power on and it won't be trying to throw you out the circuit head first.
I never thought I'd ever feel that sensation, but now I have, I don't panic when it happens. It normally happens exiting Coppice at Donington, and Cascades at Oulton Park. The front tyre has never moved, and there are times where I think I'm taking liberties with it whilst trail braking into corners. The front also has the three compound construction.
These have recently been superseded with the S22's and have even more performance! As a novice or experienced road rider this tyre won't disappoint...
QUALITY - 10/10
COST - 10/10
PERFORMANCE - 7/10
TOTAL SCORE - 27/30