As for the O.D's

275/35-18 = 25.6
285/30-18 = 25 much shorter but more options
285/35-18 = 25.9 aren't as many options

285/35/18 rs3!

Would semi slicks 265/35/18F and 285/30/18 be ok on 9,5" and 10,5" RFP1 (stock car)?

Ouch, this thread needs a revive, the gun track semi slick in my part of the world is the Yokohama AO50. They are not cheap but have an unusually long grip life as distinct from tread life. The less serious tyres include NTO1's, R888's.

And the second preferred R spec in my part of the world is the Hankook, Z221 and Z214. These perform and last well to a point but store them (properly) for a few months and they can lose their grip almost completely.

May as well ask but these days it looks like the 'my Z won't start' type questions are the limit.

200 wear 18" on 9.5 and 10" rims for road course runs. Choices have boiled down to the following but I may have missed some, Kumho Ecsta V720 and Falken Azenis RT615K+ Generally avoid Yokohamas and Dunlops because they for their price they do not deliver. So what have you racers found?

Neither.

Re71r for overall performance and the fact that they hold up to daily driving very well, especially considering their extreme level of grip. There are some newer 200tw cheater tires that give it a run for its money time wise on-track these days, but I still give the Bridgestone the nod when you consider their overall characteristics. Bridgestones always have a very sharp yet predictable feel. Probably give the Michelin PSC2s a nod also, but given their price, the 180tw rating, and that they are slower than the re71r in terms of raw laptimes, they really dont make much sense unless you drive a car that is setup for that tire, in which case they are of course worth it.

Ran across some comment somewhere that the RE71R were more of an autocross tyre but there is so much info out there that it's good to get a first hand experience. Any suggestions as to tyre sizes for the Bridgestones? I'm thinking 265 and 285.

Definitely not an autox only tire, though it can work well there also. They are just like any sub 200tw tire, they need to come to temp to really work (which will NEVER happen on the road, unless youre driving the ring).

Id just go with a square setup on 10.5s and run 275/35/18 all around. Unless you have a spec of course...

How do Toyo R888R compare? Can get them in the exact widths required.

The r888 isnt going to do anything better than the re71r. Except for maybe the tread pattern appearance, lol.

Have ordered a set of Falken RT615K+ which I realise are not the fastest but some came up at a good price and they sound like a fun tyre to drive on. Semi driftin yo.