Tyre size, 23mm or 25mm??

IME not much difference between 23 and 25mm. Would opt for 28mm regardless of your weight, you can always replace them if they're too comfy.

Ultremo ZX is a lovely tyre to ride, GP4000S and Michelin Pro4 have very similar qualities.

http://mccraw.co.uk/schwalbe-ultremo-zx-review/

If you're 11st I'd not put more than 100 psi in any of them, and even less for the wider versions. Try 90 psi then drop 10 psi and see whether you prefer it.

+1 for Schwalbe Ones, 25mm or 28mm, should be able to pick up either online for £27-£28. If you go for 28mm, make sure there's clearance, although the Defy is an endurance bike so I reckon you should be OK.

28mm

Why would you restrict yourself to a choice of either 23mm or 25mm ?

25mm if they will physically fit in your frame.

Fit 25mm tyres, they are comfier and will roll better. Have you looked at 'schwalbe one' tyres. They have good reviews.

Also if you're a big rider you will need the extra volume or run 23 mm at very high pressure.

Fit 25mm tyres, they are comfier and will roll better. Have you looked at 'schwalbe one' tyres. They have good reviews.

Also if you're a big rider you will need the extra volume or run 23 mm at very high pressure.