Have a spare set of 29er wheels with Pacenti TL28 rims (23mm internal width). Plan to use them for my Vaya build.
Are they too wide for 38-42 tires or will they work just fine?

Should be fine, I’m running 32 & 37mm tyres on 23mm internal rims on my hybrid at the moment. The 32 was tight to get on though…

reckon you’ll be alright, i have 35mm tyres on 719 mavics and theres enough clearance to get my fingers around the tyre! think the frame clearance is designed for 45mm wide tyres, however cant comment on minimum tyre width would work on a 23mm rim as not tried that

Thanks twojumpers.
At what pressures you run them?
Frame clearance is not the problem as far as i know.

The chart here suggests 40 minimum.

The chart is a bit misleading. You shouldn’t run tires larger than 50mm/2.0 inches on flow rims? Looks a bit strange to me.

The Schwalbe chart is better (more modern) although I have run tyres too wide / too narrow and its been fine. I think I’ve got them running @ about 60psi at the moment miranmtb.