A wider tire, or adding any weight to the rear wheel increases the amount of force necessary to overcome the friction coefficient of rubber on cement and begin the skid. Tread, rubber composition, gear ratio, the surface on which you are riding, weight, and its distribution are all variables in how easy it will be for you to skid. I like to run a 25cm tire on the back as opposed to a 23 as it gives me a bit more rubber on the ground. From what I have noticed there is a negligible difference in skidding difficulty.