On my single speed I run DT Swiss XM551 rims but recently I’ve preferred DT Swiss XM521s 35mm inner width with 2.6 tires. ( actually 2.5)
I found that the 40mm inner width Supports 2.8 Maxxis (actually 2.7) tires very well. DHF DHR2
When I rode the 2.8s tires on 35mm rims (WTB i35) I could feel them squirm And roll while riding hard. If you put more air in they squirm less but you loose some of the benefits.
My wheels
29mm inner = 2.4 DHR2 – 2.5 Assegai 29er
35mm inner = 2.6 DHR2 – 2.6 DHF 27.5
35mm inner = 2.6 HD – 2.6 MM. 27.5
40mm inner = 2.8 DHR2 – 2.8 DHF 27.5
All my Maxxis tires are narrower than the stated ERTRO says. The Schwalbe tires are the correct width. It doesn’t bother me but it’s worth knowing.