Samson,
I am running 245/40/18 and 275/35/18 on 8.5x18 and 10x18 custom made CCWs. Admittedly my Dunlops were stock 225 and 265 on 7.5 and 9 turbo twists so maybe that was some of it.
Your location isn't specific but I am in So Cal so temps never go too low. If you are in a colder environment that may play a part.