Tyre outer dimensions

[KneesUp]

I currently have slick tyres on 26" wheels on my bike, but last winter I swapped them to knobbly tyres when we had snow - which was fine except I had to mess about moving the mudguards as the knobblies wouldn't fit because they have a larger external diameter.

The current tyres are past their best, so I was looking at some slightly more treaded ones to replace them, because there are a few bridleways I can use on my way home which are fine on slicks in a summer like we've just had, but that are a bit sketchy on slicks in autumn. I'm loathed to keep moving the guards (especially as they now sit just right!) so, is there an easy way to tell the outer diameter of a given tyre?

 

[lazyfatgit]

Tyres seem to be a bit random between manufacturers for the same nominal size. Diameter also varies a wee bit depending on the rim width.
I have stumbled across the odd review where measured sizes are published.

 

[further]

If you state what tyres you are interested in people who have them could go and measure them.
Chris

 

[Ajax Bay]

As above.
On this quick comparison I did (not sure what the tread is on these), the width varied between 32mm and 34mm for a nominal 622-37 (acknowledge OP is looking for 26" tyres). But this is on 17mm internal width rims (and the OP's rims will likely be wider). Conversely the testers measure this for all tyres (across the several ranges) at 100psi - which the OP will never run.
https://www.bicyclerollingresistanc...arathon-plus-2015-vs-vittoria-randonneur-2015
So to get a decent answer the OP needs:
1) to share the internal width measurement of the rim
2) to determine what pressure they'll be running (depends on weight and rough width (so there's some iteration to be done there)
3) to identify some candidate make/model of tyres (with the desired amount/pattern of tread).
My experience is that height of the tyre can also be a limiting factor, underneath mudguards.