The photo of Alutech's 29er Senna pops up on my mobile phone on a boring day at the office. "Fancy a test ride in South Tyrol?" it says underneath. The sender: Jürgen Schlender, the cult welder and company patron from the far north near Eckernförde. Of course I'm up for it. But the idea of testing the device in Latsch doesn't suit me. The terrain there is too smooth. There's a blatant alternative a few kilometres closer to Munich: The 4er trail in Bolzano, rocked down to a sea of rocks after years of use as an illegal downhill route. Steep, rocky, ugly. I know every one of the smoothly rubbed boulders here on a first-name basis. I don't know how many times I've rumbled down there. Very, very often. We used to test enduro bikes here. Today, anything below 200 millimetres of travel and with less than downhill flats is close to masochism. At least if you want to ride fast. And I want to ride fast.
Jürgen brings two identically constructed models of his Senna to the test day. One with 27.5 tyres and the high-wheel model. I take the 27.5 tyre for warming up. I know and appreciate the bike as a smooth-running colleague with nice geo. With its elasticity and sensitivity, the Manitou Dorado at the front is perfect for the terror track in Bolzano. I don't love the Double Barrel air shock quite as much. Somehow I always have the feeling that I can't quite find the optimum setting with this thing. At least there is now a basic setting suggestion for the Sennes models on the CaneCreek homepage. And experience has shown that the rear suspension works well - as the same shock is fitted to both bikes, it doesn't matter in the end anyway.
After the first descent I'm warm and the 27.5 Senna is broken. Derailleur hanger off, derailleur and wheel unhealthily hooked together. Flat anyway. Sorry! Bolzano! Jürgen Schlender has a sour look on his face as he has a few photos taken of the virgin bike before the first descent on the prototype, as long as all the sweat beads are still in the right place. When I lift it up and sit on it for the first time, I am doubly surprised: firstly, the bike is really light. The big Senna achieves this thanks to the expensive carbon wheels from eThirteen with their own tyres and expensive carbon cranks from the same manufacturer. The air shock also saves a few hundred grams. Nevertheless, a total weight of 15.2 kilos is a top value. The tuned World Cup rockets of the pros aren't any lighter. On the other hand, I sit completely normally. No high handlebars, no "sinking into the bike", as is the case with some enduro bikes with a flat bottom bracket and long head tube. In fact, the bottom bracket drop and stack value hardly differ from the 27.5 model. Why? "This is the first attempt. I didn't want to go too low, the bike should still be manageable," Jürgen grumbles into his non-existent beard in response to my question. So a handy 29er downhill bike? I see. But then Jürgen has already changed the rest of the geo: the head angle is 1 degree slacker (62 degrees) and the reach is 2 centimetres longer. This increases the wheelbase to an enormous 1268 millimetres. Because a standard fork with a normal offset is fitted, the trail, i.e. the distance between the wheel's centre of gravity and the theoretical point at which the steering angle penetrates the ground, is increased. This ensures even more directional steering. I get a little scared of the bends on the track.
But this is unfounded, because after just a few hundred metres on the trail it becomes clear once again that the handling of a bike should not be derived from the numbers and data in the geo table. The 29er Senna rides almost exactly like its smaller brother. It's nimble and smooth - but not unwieldy and sluggish. On the contrary, the subjective ride feel is almost inconspicuous. The few open bends with forest floor at the very beginning of the route work better from a standing start than with the 27.5. The effect that I feel more stable with active pressure on the front wheel and outer pedal on the bends and that I come out of the bends higher is something I know from similar comparative rides in the enduro segment. On the subsequent winding forest section with lots of exposed root carpets, the bike picks up enormous speed. No getting stuck on big edges. Flow. My favourite section in the upper part is a kind of natural channel with a rocky surface. Here, my vision usually blurs due to the constant jolting and I keep one finger on the brake, even though it's almost dead straight towards the road gap. On the 29er Senna, I shoot through the canal from the second descent with death grip (all fingers on the handlebars) without fear and feel safe. And fast.
The great feeling is gone when I don't hit the jump at the road gap perfectly and pull a little too far to the left. Suddenly I'm a passenger in a jumbo on autopilot heading for the undergrowth. I narrowly miss the tree with my handlebars as I land. The large wheels have enormous momentum. Whips and changes of direction of all kinds require a lot more physical effort. But with my 69 kilos, I'm more like the bike's centre of gravity as soon as it takes to the air. No more manoeuvrability. But the Sennes 29 is not intended for tricks in the park, but for best times. Speaking of which: I've been riding here for almost two years, often monitored by Strava, and have been steadily lowering my best times in three sections and for the entire route with different bikes. I hold my record in all segments with the Commencal DH V4. Everything was just right for me with this bike: Handling, smoothness, equipment. On the Sennes 29, the slightly too thick brake levers of the Magura MT7, which also suffer from slight pressure point wandering, annoy me. The Answer handlebars are also curved upwards in a strange way. And yet I still manage to set a new best time on the first two segments of the third descent. Subjectively, I didn't leave the throttle open too much. I took almost 3 seconds off my own time on the 1.5 kilometre section. Of course, Strava always has measurement inaccuracies, but it's enough to give me a trend. And it says: I'm faster here with the Sennes 29 than with any other bike before!
Good: even on the steepest edges, I can get far behind the saddle without sitting on the rear wheel, thanks to the higher bottom bracket. However, I don't manage the overall best time - probably mainly because the unergonomic brake levers and the wandering pressure point literally slow me down in the final rocky madness with various steep sections.
ConclusionWith the Sennes 29, Jürgen Schlender has given the competition a bullet to be taken seriously. Rather open high-speed tracks are ideal terrain for this bike and pretty much everyone will be fast on it and probably faster than on a 27.5. If it's more twisty and angular, such as in Spiczak, the result may be different. But the development of geometries has only just begun. However, the Sennes 29 is an absolute specialist. It doesn't work as a fun machine in the park simply because of the high gyroscopic forces of the large wheels. Brandon Semenuk and Nicolai Rogatkin don't ride 26er downhillers for nothing when they want to do tricks. My prediction is that 29er downhill bikes will soon appear in the World Cup if they are not banned - and then everyone will want them.
Interview with Jürgen Schlender, Alutech: "Just do it!"
Jürgen, a 29er downhill bike - why?
When we test rode the Tofane, our 29er enduro bike, in 2012, we were impressed by its downhill performance. At the time, the thought crossed my mind: there's more to it!
Was that difficult to build?
No. The conversion was relatively quick. Logically, you have to check that the tyre has enough space at full deflection.
Does the very slack head angle have anything to do with the fork offset of the 27.5" Dorado? Or will it stay that way, even if there are forks with more rake in the near future?
We love the slack steering angle. It works very well in combination with the Dorado. When 29-inch production forks become available, we'll take another look at the steering angle.
What do the fork manufacturers say? A shake of the head or support?
Unfortunately, they're not saying anything specific at the moment. Only that it's a big issue and we've created a lot of wind around the topic with Senna.
What is the feedback from your team riders?
Good. Higher cornering speeds, smoother suspension, less tiring driving plus faster times. What more do you need to say?
Will 29-inch wheels also replace small wheels in downhill racing?
Counter question: What does a racer want? Answer: On the podium. To do this, they need fast or faster material. So: a simple yes.
What disadvantages do 29-inch tyres have from your point of view?
It is not yet possible to say whether they will work on all routes. Under extreme conditions, your backside may come into contact with the rear wheel.
Will the Geo remain the same as the prototype?
We are already pretty happy with the geometry. In the production bike, we will lower the bottom bracket by another 26 millimetres.
Opinions on 29er big bikes:
