I found a good interview with Cy from Cotic where he said the following:
“The only really obvious thing that we noticed was they’re just that bit…’calmer’. What it was, particularly on the hardtails, what we found was…we had this test loop and we went round and round and round, and we had all three different wheel sizes, for the three of us, you know, me Ian and Paul, we went out to Luchon in the Pyrenees in November to do like a solid week on these bikes. And we just had bikes everywhere, stems, and oh man, we just really went to town on it to really get into where it all stood. And the biggest difference was…(pauses)…it’s the whole bike pitching front to back. Like on choppy ground, the 26” bike gets this real kind of ‘pitch’ on, and the 27.5 is just a bit calmer in that respect, it doesn’t drop into the holes quite as much, the wheelbase was a bit longer, so it was just that bit more kind of…’calmer’ and more confidence inspiring a little bit. But in terms of the way it worked, everything about it, the way it manualled, the way it cornered…it was just the same.”
“Whereas the 29er is kind of a bit more kind of…lazy. You know it kind of feels like you’re scribing these great long arcs on the 29er, you’re carrying tonnes of speed, but it’s very prescriptive, whereas you can kinda…you can still dick about on the 27.5” bike like you can on the 26. And I mean, that’s the frustrating thing really, is that it’s much of a muchness.”
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I think it makes a lot of sense! That’s from Jan 2014 for context.