Before I start I would like to point out a few things, Surly recommend 35mm rims as the minimum (the Crests are narrower than that at 24.4mm, the Northpaw rims are 48mm) and the tyre used for the Northpaw rim is used but still has plenty of tread and is the same version as the new one 29x3" 120tpi.
The idea of the test was to see the profile of the tyre on the narrower rim and how much it decreased the tyre width. I pumped both tyres up to the same pressure (20 psi). I chose this pressure because it middle ground for the tyre with maximum pressure being 35psi and people going as low as 10psi. Also coincidentally it is the pressure the tyres popped into place on the Stans rims creating a seal.
The other difference is I ran the Stans rims tubeless and a tube on the Northpaw rims.
Okay I guess I should start with the installation of the tyres:
The Stans Crest rim: the Knard tyre was tight but still possible to install with just your thumbs and with the addition of some Stans fluid created a good seal, it took 2 or 3 hard pumps to create an air tight seal and for the tyre bead to start moving towards the rim edge, from this point the tyre inflated as normal and popped into place at 20psi there were a few points where the Stans fluid was bubbling out but a quick spin of the wheel and wiggle of the tyre seemed to sort this. I left the tyre overnight and it was still inflated to 19psi the next day.
The Northpaw rim: The tyre was much harder to put on because it was so floppy on the rim, the only way to get the tyre to stay on was to inflate the inner tube enough to hold the tyre in shape. Once the tyre was on it was just a matter of pumping it up. The tyre bead did rise up on the rim but I simply deflated it slightly manipulated the tyre and then re inflated the tyre again.
The side by side photos of the tyres inflated to 20psi are below the used tyre is on the Northpaw rim and gives a slightly flatter profile while the new Knard is installed on the Stans Crest rim (on the right) and has a more rounded profile.
Considering the Northpaw rims are nearly exactly double the width of the Stans Crest rims the Knard tyre width is remarkably similar. There is only a 4mm difference in carcass width and 3mm in outer knobs width...both larger on the Northpaw.