Help with width of stairs

I am building stairs to my deck. How wide can I go before I need a centre centre stringer. I am using 50mm wood.

I've not had the opportunity to build a wide flight of stairs so I checked my old theory books and they recomend 1350 between stringers using 250 x 50 and 900 between stringers for 250 x 38. imho I wouldn't go more than 1350 either as not only will you get too much spring as you use the stairs but the timber will probably cup and bow etc too much

Are you using steel stringers or timber?

Thanks heaps, that is a great help... I am using wood stringers.