I group tyres into 3 camps:
Groups 1 & 2 are road legal.
consists of just about anything that you'll find fitted to a production car, including relatively good tyres such as Yokohama A520, Bridgestone S-02, Eagle F1 (UK only), Toyo Proxies T1
consists of what are really track tyres but are e-marked and road legal. Yokohama A032R Avon ACB10, Pirelli PZero C, Michelin Pilot Sport Cup, Hoosier's and Turbospeed CR28 Sport are common examples.
The difference between tyres in Group 1 and Group 2 is measured in whole numbers of seconds on the track. At Goodwood a flying lap on A032Rs is 4 to 5s quicker than on A510s of the same size. The track tyres have *lots and lots* more grip especially when up to temperature, they don't fall apart as readily when hot, and their characteristics are much better in that they can take a bigger slip angle without losing grip. The downside of them is that they wear out much faster due to (a) a much softer compound, and (b) having less than 5mm of tread to start with.
Slicks are a big step up again from the sticky road legal tyres. Slicks do come in all varieties of hardness, the grippiest being super-soft sprint/hillclimb compounds which would barely last a couple of laps of the track.
The Bridgestone S02 saga
The S2 originally wore 205/55ZR16
front, and 225/50ZR16 rear, but the PO had fitted 245/45ZR16 at the rear. I
thought I would like the extra rubber on the ground, and decided on 225/50ZR16
front (the original rear size), and 245/45ZR16 rear (the existing rear size). I
checked the web for Bridgestone
Australia, and found listings for the tyres that I wanted, but only the 225 was
available in the desirable N3 designation (meets Porsche standards, and is
fitted by the factory).
I contacted Bridgestone Australia, and they told me that only tyre sizes as fitted to current Porsche models (Boxster and 996) were available in the N3. So I could have 205 N3 and 225 N3, or 225 N3 and 245 non-N3. Their recommendation was to stick with N3 spec tyres front and rear, hence 205 and 225. I decided that I knew better, and ordered the mixed bag.
To (finally) get to the crux of the story, I rolled up to the tyre place today to have the work done I notice the next pair of tyres lying on the floor next to the fitting machine. I see one is significantly wider than the other, and wander over to check them out. That's when I discover the error of my ways.
THE WIDER TYRE IS THE 225!!!!!!!!!!!!!!
I pick up my jaw from the floor, kick start my brain, and ask the guys to hold everything while we work this out. It doesn't make any difference, the 225 N3 is A LOT WIDER than the 245 non-N3.
The guys removed the two wheels already back on the car, and sure enough the fitted tyres show that the 225 is approx 50 mm wider than the 245.
I decided to go for 205 N3 front, and 225 N3 rear. Luckily the distributor had the 205 in stock, and I picked up the car this afternoon with four new tyres. (It feels a different car, but that is another story!) Even the 205 N3 looks to be a little wider than the 245 non-N3!