I noticed Schwalbe have listed the Marathon Plus as being availalbe as a 26x1.5 - this was very good news to myself.
I searched around and found no retailers, emailed Schwalbe to see if it was an error, but they quickly replied that it is now available in this size.
Splendid news - the 1.75 is a little large and the 1.35 a little small for me, so the 1.5 will be perfect when i can get one.
