I remember having 28's which were a breeze to skid on. I also had 23's (that had no tread whatsoever) that were much more difficult to skid with. But i've heard this argument the other way around. What's your experience with different tire sizes and the degree of traction?

unweigh the rear wheel and it shouldn't make much difference.

I do seat skids (not long extended ones) on my 25mm often enough and it isn't that difficult. I also have a low gear ratio

Only difference might be that larger tires are heavier and may require marginally more effort to stop the wheel. But then again, all tires are different weights per manufacturer/model, so who knows. There is a much bigger difference in tire function and compound.

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.

thanks, I think my experience may have occurred due to the amount of tread being the primary variable