I'm running 9" monoblocks front and rear, with 15 mm spacers. On the front I have 245/40 tyres, and on the rear 275/35. These are within 1 1/2 % of each other as far as circumference is concerned, so no probs with ABS/Cruise control etc. I don't think you can realistically go bigger than 275 on the rear, and on the front anything wider than 245 will lead to fouling with the fenders. With this set up, the car is very "taut" and very responsive on the steering, which is what I wanted - a good balance between looks and performance! You could possibly try other combination of tyre sizes, but be careful to stay within the 1-2% tolerance between circumference to avoid other problems? Xxx