Well…..Tootyred…as with most things there is a lot of different things going on.…
26 was a pretty arbitrary adoption of standard - which enabled good clearances at the time, with typical ‘double diamond’ mentality for geometry brought over from road bikes. Don’t forget that there was an outbreak of 26er road racing bikes for a year or so. Long gone. In MTB the 26 format was heavily elaborated and settled, then people started playing with geometry, tinkering by Gary Fisher and others, then partially fuelled by the DH design which was going on, where bigger hoops (650b) enabled better progress in rock gardens and over drops. There was a definite performance thing going on, not just marketing - although that indeed was going on too. The small fabricators didn’t really care whether they sold 26, 27.5, or 29 - indeed they just had to run to keep up with demand.
I was sceptical with a BIG S of bigger hoop size. But decided to play. First some Ragley 27.5s for my son and I - impressive things - an mmmbop and a Marley. Very impressive design and beautiful fabrication. And then we started playing with the DH bikes - and he just romped away on a Canyon Sender DH 27.5 compared to my Orange 26er. We still love our 26 Inch bikes - jump bikes and a 26 Simple and 26 Stanton ti - but you can stuff the Ragley 27.5 hardtails into rock gardens which would terrify me on 26, and throw them down drops which would have me over the front on a 26er with a 69 HTA and 120 stem. I was interested in 29, and so started building. Hardtails. And then FS. What I learned was they needed very careful design, and huge attention to minor details such as fork offset. But I really appreciate my 29ers - FS and Hardtail - marketing they are not.
It was clear on the Welsh trips this year that yes, you could ride all the trails on a good 26 er but if you wanted to throw yourself down things at warp speed then 29 really, really helped. Now, while on my 29er FS I couldn’t catch my son on his 27.5 Transition FS, it was notable that the very experienced folk with us on 26ers were way, way behind.
That does not make 26 redundant, weird or old-fashioned. I just see it as a different way of proceeding. The days I have out are still gorgeous days out in nature. But when I am tanking through the woods and hauling big terrain, I quite like my big hoops. If we had started on 29 in 1981, I still think we would have 26 inch jump bikes and youth bikes around...