En esta entrada voy a analizar a la nueva Yeti SB5.5C 2016, un modelo muy interesante ya que es la primera vez que Yeti apuesta por una 29er de largo recorrido y con una geometría mucho mas agresiva que la de la antigua SB95. Este modelo tiene 140mm de recorrido traseros y una horquilla de 160mm, una geometría espectacular con 66.5º en la dirección y unas vainas de tan solo 437mm. El eje trasero es tipo Boost, pero el cuadro no es compatible con ruedas de 27.5+, algo que tampoco está mal del todo. Yo soy partidario de crear cuadros específicos para cada medida de ruedas, el reciclaje de piezas nunca da buen resultado...
Como podéis ver en la tabla de excel y en las gráficas anteriores el sistema de la Yeti SB5.5C tiene una Eficacia de Pedaleo muy alta, pero el porcentaje de Anti-squat en los desarrollos mas largos vuelve a ser un poco excesivo (+150%). Dentro de unos meses sale a la venta el nuevo grupo Eagle de Sram y la verdad es que es algo que le vendría muy bien a este modelo, ya que con un plato de 34T o 36T los porcentajes se quedan mucho mas cerca del 100%. El Pedal-kickback (18º) como es lógico es bastante elevado, al igual que el Brake-squat (95%), uno de los puntos débiles dentro del sistema Switch Infinity...
En la gráfica del LR vemos como el sistema es prácticamente lineal (2.5~2.45), unas cifras muy similares a las de la Yeti SB4.5C, pero en este caso el problema es mayor, ya que estamos hablando de un modelo que va a recibir un trato bastante duro y que ademas viene equipado con una horquilla de 160mm, por lo que el conjunto puede quedar desequilibrado... En estos casos la elección del amortiguador se convierte en algo extremadamente importante y aunque Yeti equipa a este modelo con un Fox Float-X EVOL de 200x57mm, creo que hay margen de mejora y lo ideal sería utilizar un amortiguador de aire tipo CCDB Air, FFX2, RS Vivid Air, o incluso un amortiguador de muelle de gama alta.
Un saludo.
En la gráfica del LR vemos como el sistema es prácticamente lineal (2.5~2.45), unas cifras muy similares a las de la Yeti SB4.5C, pero en este caso el problema es mayor, ya que estamos hablando de un modelo que va a recibir un trato bastante duro y que ademas viene equipado con una horquilla de 160mm, por lo que el conjunto puede quedar desequilibrado... En estos casos la elección del amortiguador se convierte en algo extremadamente importante y aunque Yeti equipa a este modelo con un Fox Float-X EVOL de 200x57mm, creo que hay margen de mejora y lo ideal sería utilizar un amortiguador de aire tipo CCDB Air, FFX2, RS Vivid Air, o incluso un amortiguador de muelle de gama alta.
Un saludo.
13 comentarios:
Un saludo,
Siempre me gustaron las Yeti pero la extra-complejidad/encarecimiento del Switch Infinity me parece excesiva. Cuánto afecta realmente a la suspensión? Se puede incluir fácilmente su efecto en los cálculos que nos muestras?
Gracias Maestro.
JMK29
El sistema de railes es básicamente una bieleta con una longitud infinita, El programa Linkage no te permite incluir un rail, pero puedes colocar una bieleta de dos o tres metros con la misma orientación y al final el resultado es el mismo...
Un saludo.
please do Devinci Troy 2016 model!
Lástima, el concepto se les ha ido de las manos aunque pongan detrás 50 dientes... pienso como opinión muy personal, que un 29 exige siempre dos platos al menos. Pero al hacerlo así pierden uno de los puntos fuertes de esta cinemática, el pk tan agradecido de otros modelos en relación a un AS planito....Ganadora en este bautismo de 29s agresivas: la YT.
You always know what you are getting with Yeti. They have their preferred geometry, AS and AR curves, leverage ratios etc. And it is always pretty impressive.
Antonio, I would like to ask an oblique question. I note that there has been a small change in the graphs of the BMC Trailfox 29 comparison bike. You said long ago that your own analysis indicated that bike was shorter travel than advertised. The graphs are now showing 145mm of travel, not the advertised 150mm but a bit longer than your earlier analysis indicated. Would you be able to elaborate on the changed details in the graphs, please?
Un saludo
Chris
You could safely go to a 34T with the SB5.5C. Maybe, even a 36T could be made to work (assuming the gearing impacts are acceptable to the rider). It would be interesting to look at whether the AS numbers were a little bit more consistent irrespective of rear cog selection if the front cog used was a bit larger. Antonio, would it be too much to ask for you to add Excel data for the 36T?
Un saludo
Chris
Thank you Antonio. It looks like the 36T is the jackpot for this bike.
Un saludo
Chris
To L Train... Devinci Troy is finally done.
To Chris... I'll never be happy with the BMC model, I have done it a lot of times and I always get 140-145mm of travel but I still think that the difference is too big and Swiss people are very serious so it's a really weird situation. Last time I checked I got 145mm and that's what I'm using now in the graphs, but I would love to get the blueprints of that bike and build a 100% accurate model.
Best regards,
Tony.
Years ago, on this blog, I can't recall where exactly, I expressed a faith in the value of 2By chainring combinations. I set out an argument about certain possibilities - a narrowing of the gearing range between the two cogs of a 2By crankset complemented by an increased range (and probably number of cogs) across the rear cassette - that if implemented would bring big benefits for all MTB riders. I saw 1By as technically interesting and useful for racers but not as something with more general relevance for all riders. While my faith in 2By hasn't entirely waned, looking at the new Yeti bikes I now think I missed the richness of possibility opened up by the 1By drivetrain.
What is notable about the Yeti bikes is that they are using a 34 or 36T as the default chainring for the 1By setup (1By bikes normally ship with something smaller) and moreover using those chainrings optimal pedalling is achieved i.e. AS is around 100% at SAG. Too many 1By bikes would ship with a 32T chainring, say, but optimal pedalling would require a smaller cog, a 28T, perhaps. And, as it happens, racers would then toss the default chainring and put something larger on there, because they just didn't have the speed they needed for racing. As I see it, the results of all this weren't too good. Many MTB riders were feeling the loss of some of the lower and higher gears and racers were having to sacrifice low gears for the sake of outright speed. No riders at all were getting optimised pedalling on 1By bikes of this sort. Thanks goodness for LSC damping!
One of the things that makes these Yeti bikes so interesting is the significant difference in the preferred implementation of a 1By drivetrain compared to what most of the other manufacturers are doing - Santa Cruz are amongst the few others that appear to be leaning in a similar design direction to Yeti. Interestingly, if you add one of the newer 12 speed rear cassettes with a super-wide gearing range to a Yeti bike, e.g. SB6C, SB5.5C or SB4.5C, the result is a bike with good low and high range gearing, that pedals well, that has little need for LSC and that is suitable for common riders and racers alike. Besides being an exciting prospect for riders that appears to be proof of the value of the 1By design approach.
So, I guess I have become a supporter of 1By drivetains for MTBs. But that assumes i) use of a 34 or 36T chainring ii) optimisation of pedalling for the 34 or 36T and iii) use of a super-wide gearing range rear cassette. Without all of those elements, 2By remains viable and useful.
Un saludo
Chris
Okay, I have rather confused things - in a fit of excitement, I made false assertions about the drivetrain configuration of current Yeti bikes. The Yeti bikes (all of them it appears) currently ship with a 30T chainring, not 34/36T. That makes sense from gearing point of view because those super-wide gearing range cassettes are not shipping yet. I would guess that such a cassette will be specced at some point because the Yeti bikes do cry out for a 34/36T chainring from a kinematic point of view, but use of the larger chainrings pretty much depends on the presence of a very wide gearing range cassette as a prerequisite.
So, if you can forgive the wobbly presentation I gave of the key points you will notice that the bike setup I described and advocated makes sense in many ways, even if only as a future possibility. The larger chainrings would improve the pedalling performance of the bike by trimming back on the elevated anti-squat produced by the 30T.
The Yeti bikes appear to be future proof - the existing design already anticipates the inclusion of parts with a new design that when used actually can improve the performance characteristics of the current bike, or that at least is how things look to me.
Un saludo
Chris
I don't think they are future-proof by design, it was all good luck. Nobody knew until a few months ago that the Sram Eagle was coming and this new bikes were designed one year ago, so they probably didn't knew. Yeti designers simply like this type of systems, and if 1x12 becomes the norm in the next years, they are probably going to design their next bikes around a 38T or something along those lines...
Best regards,
Tony.
Antonio, excuse my ignorance, is the ultimate goal to have a bike running near 100% anti-squat, when in the power climbing gears?
In the case of the Yeti 5.5, you have found that the larger the front chainring, the closer to this ideal 100% you can obtain? Even if this requires operating in a lower (physically larger) gear on the rear cassette?
So for instance:
1) My current set up,running a 30 tooth front, while climbing mostly in 3-4th gears on a TRSr rear cassette (33t & 28t respectively) will result in excessively high anti-squat numbers that are less than ideal?
2) Instead if I run a 32 tooth front, while climbing mostly in 3-4th gears on an Eagle rear cassette (36t & 32t respectively) will result in improved anti-squat numbers being closer to ideal than option #1?
3) And the last option, running a 34 tooth front mostly utilizing 2-3rd gears on climbs will provide the most ideal anti-squat on this bicycle?
Running 30% rear sag. are the above assumptions all true?
Thank you
Here are a couple of my issues that I think are relevant:
Yeti's spec claims and/ or your analysis of what are probably pre-production or photoshopped images to reach your numbers, results in what I suspect our inaccurate results. Maybe slight, maybe not.
A couple of notes that I can leave, but no real answers provided by me:
1) The ACTUAL HT angle of the L 5.5 is 66.1 as accurately measured not under sag.
2) The actual chainstay length of the L 5.5 is 430mm.
3) My size L frame won't clear anything larger than a 34 tooth front rotor, and that's using a 3mm offset. If you use the correct 6mm boost offset, it's going to be very close to clear even a 32.
Just an FYI.
I will swap to eagle, and increase front rotor size from 30 to 32, and report back if I feel less hanging up on edges and what not.
~ take care
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