I have a recipe for a pizza dough, that was originally with yeast (500g flour and 300ml water). I tried to make it twice now with sourdough. I took a bit of starter, mixed it with a 50-50% flour-water mix, let that rest for around 10 hours and than took 160g of this mix and figured since it's 80g flour and 80ml water, I now only need 420g flour and 220ml water. Now this sounded like a good plan, but both times the dough was a bit too wet and sticky compared to what I used to get when I just did the original 500g-300ml with yeast, so I ended up adding a bit more flour to the dough. Is this normal or am I not getting something here?
Sourdough doughs behave somewhat differently from those made with only baker's yeast. It's hard to predict, but the combination of acid produced in the sourdough and other components can make things weird, particularly during long fermentations with sourdough. Studies have shown that sourdough fermentation breaks down various components in the dough chemically in a different way from fermentation with baker's yeast.
I made pizza dough with sourdough starter a number of times, but I've stopped doing it because I found it so unpredictable (as I used a longer fermentation dough). Yes, it often turned out more sticky for the same level of hydration. Stretching it was also unpredictable too. Too much acid, and your gluten will break down, allowing the dough to tear much more easily. I think this may be related to the "stickiness" issue as well. I've had pizza crusts literally rip apart on the way into the oven when I was trying to unload them from the peel. I've had holes appear during unloading with regular baker's yeast, but I've never had straight ripping apart as I've had on a couple different occasions with sourdough.
Anyhow, I don't want to make this answer about me, and I know I could modify the technique to make sourdough pizza more workable. (Lots of people make sourdough pizzas successfully; I was just trying to maximize flavor a little too much.) My point is that from my experiments with it, the dough behaved very differently, even with the exact same recipe, with the same hydration and other proportions.