One of the most striking aspects of the switch from 26" to 27.5" wheels a few years ago was that the speed difference manifested itself more clearly on downhill bikes rather than trail. Taking that size up again exposes the rider to an even greater transformation of pace across the ground.
Words and images: Steven Jones
For whatever reason there has been a certain reticence to adopt the bigger wheel by many on the enduro circuit and a handful of pro DH riders have voiced their opinions of 29" wheel bikes very clearly on instagram. Many without having tried such hardware. Such comments only show the cluelessness of those that make them, maybe it's better maybe to at least have some experience of the subject before giving an opinion or getting all xenophobic on wheel size.
Indeed I travelled to the hills east of Los Angeles with a certain amount of fear myself. Knowing the capabilties and pace of 29"x160mm bikes, the prospect of even more travel and a big Fox 40 up front, on a decent track, with Trek’s R&D boffins to hand filled me with a mix of apprehension and excitement.
Trek Suspension R&D, Santa Clarita, Los Angeles
It might come as no surprise that the suspension on one of the most successful downhill race bikes of all time, the Trek Session, didn’t just happen by chance. Within a few short years the Session went from prototype to World Cup success, it enabled Aaron Gwin to win not only his first race but to capture the first ever male series title for an American rider. That was in 2011.
A few years later Trek introduced carbon into the equation and shortly after the first 27.5" wheel production carbon downhill bike. Tracy Moseley was incredibly successful on the Session and Rachel Atherton has been unstoppable since moving to Trek and last season was unbeaten at downhill events.
In testing that we have done on the Session the suspension, particularly in the last four or five years has been a cut above. It builds momentum in the bike, the rider fully understanding a simple but very efficient system. Sensitivity, support and balanced in the corners. It sounds so, so simple but we’ve ridden most of the production downhill bikes and you cannot say that for a large percentage. Ok we’d like to see a bit more ‘give’ in the rear swingarm, a slightly lower bottom bracket, but the suspension has been superb.
The Session is lively and its simply great everywhere. A true race machine of which there are few. Jose Gonzalez is head of the LA based R&D unit and has a very specific idea on damping/suspension. “Mid stroke support and control is critical. Mid stroke characteristics defines the ride dynamics and dynamic geometry the most. It influences stability, control, cornering and it’s critical to good deep stroke control while maintaining good push thru for consistent use of travel.
Additionally, balancing the mechanical system (kinematics) with the shock and vice versa is very important for a balanced performance. I’ve never understood how some designers can claim that you don’t need compression damping if you have a certain mechanical system. Dampers are transient devices where a mechanical system is not, meaning that a mechanical system operates the same regardless of type of input/bump whereas a damper is very sensitive to the type of bump."
It was with Jose and his right hand man Jason Lindenberg that I met to ride this prototype bike. The Session 29 after all lives with these guys, it’s with them that the different challenges of balancing a bike that’s going considerably faster are trusted to. “The main thing we’ve found is that you’re able to carry more speed on the 29" wheel and you’re a bit more stable due to the greater self-correcting nature of the bigger wheels, so you can drive in more “monster truck" like. Also, the bump frequency changes a bit when compared to going through the same section on 27.5" wheels. Fast cornering also becomes calmer on the 29" wheel which influences things as well."
SESSION 29 - ON TRACK
The meeting place was set for a mountain pass in the hills that flank the madness that is Los Angeles. It was an early start, and even with clear blue skies the air was still crisp as the Peterbilt’s charged into and out of this great metropolis. Moving up into the snow covered San Gabriel mountains we tracked the Union Pacific as dirty air became clean, railroad turning to dirt track.
It didn’t take long to get rolling, the raw aluminium bikes looked stunning, having just had a refreshing run out with Gee Atherton only days previously. I was fully aware that my first run would be nothing less than a bracing encounter.
Out of the blocks the pace of the bike is frighteningly apparent, and exiting the first corner the need to be vigilant was gripping my senses as much as the amount of rubber was tearing into the turf. This was all about being wide awake. It only took a matter of corners to realise I was totally out of my depth on the Session recognising very quickly the potential of the bike. It wasn’t just about speed on the straights, it was the potential EVERYWHERE.
The bike is very much a Session in its ride character, easy to understand, supple, supportive, and even though the bike had slightly less travel than the current production downhill bike you just knew that the bike would get your back if things got slightly out of shape.
It was in the rock sections that you discover quite how much a big fork matters, how much trust you put in it, your front man when things get hectic. You don’t arm wrestle a Fox 40 through rocks, you simply walk all over them. At speed. Oh the speed. Even if the clock shows a fraction of second difference, the difference on this bike is definitely perceptible.
The track dropped steeply over some big boulders and its here the good and bad of big wheels comes into scrutiny. On the plus side, you can nose dive the bike without it tucking under, I tried this on a few occasions and whilst on trail or enduro bike it still offers an a advantage over 27.5" in this situation, the big 40 allows even more of that. Clearly nose diving is poor rider technique however we’re seeing the pro racers adopt even more front wheel placement so the big wheels will clearly be of use in beaten up ground.
On the downside there is a tendency for the rear tyre to buzz your bum on super steep stuff, and we’ve heard from other brands that riders have complained that they cannot run their seats in the usual position. A seat re-design might sort that out but there are issues around running more travel on 29" DH bikes that need tackling.
This particular Trek runs around 180mm travel. The question is does it need the full 200mm or beyond? That’s a complex question. Even though it seems this bike can match and even beat the speed of 200mm x 27.5" bikes there is always the need for more. Just because.
Wheels and tyres have clearly been the sticking point with long travel 29" wheel bikes until now but they are very much here and this Session was never underpowered in that respect. The bike had been ridden that’s for definite but still I look forward to exploring some different wheel and tyre combinations on the big travel bikes.
The comparison with 27.5" wheels is interesting. Even though a 27.5" wheel bike feels more lively, it’s simply a feeling, we’ve known this for many years. You feel fast because the bike is moving around a lot more. However……the big wheels, with a BIG fork mean even more composure which in turn mean even more speed. There is certainly some mileage in the fact that 29" wheels can feel dull, that many riders cannot interact with the terrain like a 27.5" wheeler. This is simply because we as humans (most of us at least) have yet to have the capability to push them hard enough.
Adding more travel and more stability to big wheels takes the game to a whole new level, one which I believe will take some time to adjust to. Having top racers on these wheels laying to waste technical terrain is a scary prospect. Yes the possibilities are truly frightening.
Clearly there's only so much we can say on this prototype bike which might or might not ever reach production, however having ridden this bike I can see why some racers fear 29" wheels coming to downhill. Because riding a bike like this is pretty intimidating.