Has anyone any experience of running the 235 size Kumho on a 8 inch rim? Does it fit and is it any better than the 215?

They would be better on a 9" wheel (optimum wheel size for the 235).
The optimum wheel size for the 215 tyre is 8".

The 215's will do the job better on the 8" rims for less £'s

http://www.racetyres.com/kumho-track-day-tyres/kumho-ecsta-v70a-trackday-and-road-leg al.html

Thanks, that was just what I was looking for. I'm really wanting every bit of traction I can get and wondered about the wider tyre. But as you say, if I don't go for wider wheels, it maybe just spending cash to trade one problem for another.

In that case it's 215's on your rims.
In super soft compound they are a great tyre, even in the rain on track they just stick.

Yes! I ran those last year and really impressed with them. They don't look like a wet tyre but they're the best I've tried in the wet, which is just as well as it rains continuously at Knockhill

Hi David, as Carl says they are suited for a wider rim. I have used them for quite a time on the 8.5" rim and they fine, have also seen many racers use them on the 8" with no issues, in fact they maybe better than we think on an 8" rim as it would raise the rolling circumference slightly which is my problem with using them!
They like a lot of camber and I found they seem to peak performance at around 22psi

Just an update on this. Due to supply issues, I could only get the supersoft in 235 size. So I put them on the 8 inch rims for an event last weekend and they were fine. It was difficult to say whether they were better or worse, but perhaps the felt a little looser. They grained up more than my previous set but there could be many reasons for that.