Just to re-enter the tyres thing ..... i'm confused ..... again ...
I have a Raleigh MTB frame, canti brakes, with 26 x 1.75 tyres .......
Its a lovely frame and i want to build up a road / off road / forest track ..(sorry "Gravel" ) drop handlebar bike based on it ..
I also have a lovely pair of 650B wheels, hand built by SPA Cycles ...given free by a nice lady...
Now .......... are these 2 wheel sizes basically the same ?
Assuming they are interchangeable ....
What 25mm (ish) road tyres do i buy for the 650B's ..... puncture strip Vittoria's perhaps .... cheap is also good ,,,?
This looks like a non-starter to me.
The Spa wheels have a diameter of 27.5", although it's the radius that is crucial to whether the wheels will fit in the frame.
That's an extra 3/4", which would almost certainly make the wheel - plus tyre - foul the fork and seat stay bridges.
Next problem is the brakes.
Canti blocks have some up and down adjustment, but I doubt there is enough upwards to prevent the blocks attempting to grip the spokes of the Spa wheels.
Then there's the hubs, and then there's the dropouts - one or both could easily not fit.
Oh, and have we even established if the Spa wheels are suitable for rim brakes?
Lots of modern wheels are disc only.
If you can get over all those possible snags you would deserve the title of Fettler of the Year.