Pot holes

[ourclarioncall]

If I encounter pot holes

Will it make much of difference what the wheel size is? 26” v 650b v 700c ?

[PH]

In what way?
The larger the wheel the greater the chance of rolling over it, the smaller the wheel the more chance of it falling into it... but the smaller wheel in inherently stronger.
The bigger the tyre, the more cushioning the rim gets.  Swings and roundabouts. 
I think I've once had a pinch flat from a pothole, that was on a 26" wheel with a 1.75" tyre, and that's it, or the only time I remember and I only remember that because my companion rode all the way back up the hill to see where I was, which we still laugh about...  Simply not something that would influence my choice of wheel size, or anything else.

[JohnR]

650b with a 50mm tyre has almost the same rolling radius to 700 with a 30mm tyre. The 650b wheel size is effectively a way to provide clearance for fitting fatter tyres on a bike designed for 700 wheels. A fatter tyre has better ability to absorb the impact of hitting a pothole.

[martinf]

If I encounter pot holes

Will it make much of difference what the wheel size is? 26” v 650b v 700c ?

Not much. Being the largest diameter 700C is theoretically better, which explains the current 29er trend for ATBs, but I reckon the most important thing is tyre width. A reasonably fat tyre aids comfort and protects the rim to some extent from rocks and potholes.

26”/650b/700c are all significantly better than 16"/20", which I have also used on mild off-road riding.

For a 26" wheel touring bike that is used occasionally off-road (my case) I use lightweight 50 mm width tyres (Marathon Supreme), which are a reasonable compromise of good rolling resistance on good roads and still acceptable on mild off-road (tracks, footpaths).

If planning more off-road use I would go to Marathon Duremes in the same width, still lightweight but a bit slower and probably better able to resist rocks, with slightly more grip. For expedition type rides I would probably go for something like the Marathon Mondial, either in the same 50 mm width or slightly bigger if compatible with the mudguards.