RIDE – Apprehension of my first encounter with 650+ was transformed to excitement within a couple of turns, twenty foot of limestone, and a delta of douglas root. Anticipating the worst on a wild entry into a flat left I was embraced with grip, pulled into a cuddle and thrown a saddle bag of grip before trotting off into the sunset. Elated on a deflated tyre. Whatever next.

Well, the tyres continued to give, roots and rocks pushing into the carcass of the thin Purgatory rubber, conforming to ground debris, isolating the chassis and rider from the same type of vibration encountered on standard tyre sizes and pressures. As a giver of confidence this was generous stuff. Off cambers, root riddled conifer woods, flat clay skate sections, it continued to amaze – improved traction? Yes.

Day two of increased adhesion dawned gloriously wet and miserable. But before that some surfaced table tops, washed out sandstone beads, harder grounds where the heightened roll over performance and ability to straightline rock sections became a clear advantage but so too the bounce, the slightly hard to control space hopper effect on take off, landing and many of the bits in between.

DETAILS – Rims. Tyre combinations and avoiding generalisations.

In many ways it has taken a while to get used to the ways of the bigger tyre similar to the period of adjustment it took to get used to 29” wheel bikes. Different timing has been a key here too. The less than aggressive pattern of the Purgatory/Ground Control tyres combined with the 29mm rims gives a very round profile with relatively little edge. It’s a combination that leads to pretty normal cornering characteristics and certainly quite different to the 40mm wide rim/Nobby Nic tyre combination we’d ridden on the Scott Genius Plus bike.

“in muddy conditions the tyre sheds more dirt than standard 2.35 tyres partly due to the increased flexing because of low pressures”

So we mounted the Stumpy with the more aggressive but slightly narrower 2.8” Schwalbe Nobby Nic tyres in Pace Star compound and (obviously) found quite a different ride characteristic, offering more bite in cambers. That said, the compound felt better on the Specialized rubber. We also found the bike stood up a touch in the corners with the Schwalbe’s fitted, not quite as much as with the 40mm rims, and something we didn’t encounter on the Specialized rubber. This could be rider error – braking when there’s no need to and also the fact that in muddy conditions the tyre sheds more dirt than standard 2.35 tyres partly due to the increased flexing because of low pressures. The tyre clears well and regularly has more bite on offer.

In terms of rims the bike features 29mm wide Roval Traverse rims taking a markedly different route to other bike companies who run upto 40mm rims on the wider tyres. In short we’re not convinced that wide rims actually help at all, happy with the standard 29mm rims although found a nice balance at 35mm too.

Rolling speed. There is an idea that the big tyres are sluggish and don’t roll very quickly. This is a myth as we found on longer day rides where climbing is definitely easier.

As for timed testing the bike seems to yield different times in different conditions. Having ridden and timed the Stumpjumper against a variety of bikes, in different locations and surfaces we simply cannot draw any reliable conclusions yet. The tyres work better in some soil conditions than others. In fact every track hit us with different results. On muddy flat, rooty tracks the 6 Fattie even with the low profile Purgatory/Ground Control rubber was close in times to 29” with mud tyres and faster than standard 27.5” with normal dry rubber. Then on long rocky descents as found in Bike Park Wales the times compared with standard dry rubber was too close to call even though we were getting more tired on the standard rubber.

Yet even though the timing has proven inconclusive, and track specific, and the poor compound is not ideal, we found more poor compound is better than less poor compound. In other words a 2.8” Pace Star Nobby Nic had considerably more grip than a 2.35” Pace Star Nobby Nic. And the super low profile Specialized Purgatory/Ground Control 3.0” tyres offer more grip at lower pressures than a normal tyre with higher pressures. There’s a lot to take in.