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Added a comment about feature FIRST LOOK: Commencal Supreme V4 4/14/2015 10:35 PM
C50

Are you aware of any attempt to quantify losses for the Hammerschmidt? That would be interesting information to have. Also, there is the question of the overall rotated mass which you have emphasised - it is serious enough but on a Hammerschmidt style device perhaps less of a concern than for a full gearbox. Still, the overall picture isn't only about losses but also gains. If a rider can go quicker and safer in enough places because of the unique benefits of a certain suspension and drivetrain setup then that is the offset that justifies any new inefficiencies. Some inefficiencies are manageable rather than fatal. This kind of thing is best proved on the race track.

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Liked a comment on the item FIRST LOOK: Commencal Supreme V4 4/14/2015 9:13 AM

Why don't you think it would work as well for AM? Natural anti-squat and more sensitive suspension to small bumps and square edges sounds good to me. GT has employed medium height pivots with success. Mavericks simulated high pivot worked well.

Added a comment about feature FIRST LOOK: Commencal Supreme V4 4/14/2015 9:07 AM
C50

For the reasons already mentioned by @Primoz it is difficult to commit to a design like this for anything other than DH. That enduro bikes are being sold with 1x drivetrains does not mean that all designers or riders want to forgo the option to use 2x (or even 3x) drivetrains - multiple chainrings suit general trail riding better and are a good option for riders who never intend to take their enduro bike into competitive racing. But bikes designed with this kind of drivetrain - idlers and chain rerouting - are pretty much 1x only, and a lot of riders may balk at that. There is a solution though - the now almost forgotten internally geared crankset. If people really like this bike design they should call for greater effort from the manufacturers for something along the lines of the Hammerschmidt but revised and updated to be suitable for use in current enduro bike designs.

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Added a comment about feature FIRST LOOK: Commencal Supreme V4 4/14/2015 8:35 AM
C50

I certainly hope that happens. Unifying suspension bike design across all bikes in a future V5, as happened with the V3 range, would be great. But, even if something like that might happen down the line it is still years away. For now it looks like only this V4 bike will be truly outstanding.

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Added a comment about feature FIRST LOOK: Commencal Supreme V4 4/13/2015 12:34 PM
C50

Yes, a 100% Brake Squat (Anti-rise) is about as good as you can do to minimize unsettling chassis motion (rise at the rear that may also be accompanied by dive at the front) occasioned by braking but you should not assume that rear end traction is necessarily best served by a 'high' BS strategy. Different design strategies may be called for when optimizing rear braking for the sake of preserving bike geometry (i.e. a neutral or 100% BS strategy) as against optimizing rear braking for the sake of preserving traction. Transient forces at the contact patch under braking have a big impact on traction. As it happens braking configurations with relatively lower BS tend to have less sharp variations in these transient forces and gradual changes in load at the contact patch are less likely to cause loss of traction.

None of this implies that lower brake squat designs are free of problems. They are at a disadvantage compared to higher BS bikes from a geometry equilibrium point of view. Also, if a bike has brakes with poor modulation there is nothing that low BS can do about it. And there is a world of difference between having to slow the bike with the rear brakes on a relatively flat surface while heading into a sharp turn (low BS would in general be advantageous in this context) as against finding it necessary to use the rear brakes with the suspension already heavily compressed in a rock garden, say. BS of around 100% tends to interfere less with designed and intended suspension operation in a situation where it becomes necessary to brake while traversing rough ground.

Sadly, with braking, nothing is simple and not just the percentage of BS but also whether it is rising or falling also affects bike behaviour during deceleration. Some horst-links, split pivots and ABP bikes (Trek) have BS curves where the BS starts low and rises over the travel range. I suspect that is the best arrangement overall. The i-Track suspension designer seems to hold this view - see http://www.i-tracksuspension.com/suspensiontheory.html

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Added a comment about feature FIRST LOOK: Commencal Supreme V4 4/13/2015 10:53 AM
C50

While there are apparently a number of different drop-out options, the statement that, "the static chainstay length is 430 or 435-mm" does not sit well with the geometry chart that indicates the chainstay length is 425mm. And what is being referred to when the writer states, "it is still shorter on the SUPREME DH V4 (450mm rather than 457mm) to maintain a lively bike." Maybe these numbers actually mean something but the relevant explanations are missing.

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Added a comment about feature FIRST LOOK: Commencal Supreme V4 4/13/2015 10:23 AM
C50

A few of your critics have not grasped your point, apparently. That is not too gracious considering you acknowledge that the bike would, "eat steep, rocky stuff for breakfast." But that lengthening rear-centre that is the great advantage of high pivots in rocky stuff - it assists the quality of shock absorption and reduces the loss of bike momentum while ploughing through rough stuff - is also the bane of these bikes in high speed cornering especially riding berms. The suspension of all bikes packs down slowly in these situations and in this context a lengthening rear-centre is not optimal for the maintenance of momentum i.e. carrying speed. Quite the opposite, bikes with rearward axle paths will tend to slow down a bit more in this scenario than those with a more conventional design. That is not too serious but a lot of riders report a degree of sluggishness accelerating out of corners, which for racers at least, is quite important.

That said, Commencal seem to have done what they can with respect to LR escalation to provide support just at the points a design of this sort tends to exhibit its less endearing qualities, so that could go some way to mitigating any shortcomings.

Finally, there is no need to make guesses about the Anti-squat curve or wheel rate graphs etc. for this bike. linkagedesign.blogspot.com.es will normally have a full kinematic and dynamic analysis of a bike posted shortly after sound information on the bike appears. There is a translator included on the site that makes reading in English and other languages easy.

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Liked a comment on the item FIRST LOOK: Commencal Supreme V4 4/13/2015 9:24 AM

It feels awkward to say the least when you are railing a corner and the harder you push, the longer the bikes gets (a la zerode).
I am sure it eats steep, rocky stuff for breakfast though....

Hopefully it pedals better than Zerode....

Added a comment about photo WINNING BIKE: Gee Atherton's World Champs GT Fury 27.5 9/8/2014 5:05 AM
C138_nor14_26a8131

It will be very interesting to see precisely what the geometry of this bike is when the Atherton replicas emerge. Top level DH racers will generally want a bike they can win on. On the evidence, the changes GT have made during the season have resulted in a better race bike.

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Added a comment about feature First Look: Radical New 2015 Specialized S-Works Demo Carbon 8/30/2014 9:51 AM
C50

@boomslang Well, thank you for your informative comment. I'm sure that there is a lot there of general relevance for DH bike frame design and construction. You wouldn't be too shocked to learn that there are those of us who continue to consider the older frame design to be the better one overall. So, I welcome the news - widely reported and I hope reliable - that a 27.5in version of that bike will continue to be available in aluminium.

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Added a comment about feature First Look: Radical New 2015 Specialized S-Works Demo Carbon 8/29/2014 2:51 PM
C50

@boomslang I am very interested in what you have said. You seem to have an intimate knowledge of the new Demo. Are you connected with the Demo design group or are you researching this in some other capacity?

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Added a comment about feature First Look: Radical New 2015 Specialized S-Works Demo Carbon 8/29/2014 2:25 PM
C50

A good analysis by Antonio Osuna of the 2015 Demo kinematics has been published at http://linkagedesign.blogspot.com.es/2014/08/specialized-demo-2015.html.

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Added a comment about feature New Rocky Mountain Flatline Nearing Production? 8/19/2014 2:36 AM
C50

My explanation probably could have been better. The point is that a rising (or upward sloping) anti-rise curve (to see what a rising AR curve (or graph) looks like go to http://linkagedesign.blogspot.com.es/2014/08/transition-patrol-275-2015.html - the Transition bike, while it has less travel than the RM prototype uses a similar linkage design and would exhibit similar pedaling and braking characteristics) is considered by many able designers to result in good traction while braking. Almost all suspension bikes designed by Dave Weagle, Specialized and Trek use a rising AR curve. Go to http://www.i-tracksuspension.com/suspensiontheory.html for an account that sets out the supposed benefits of a rising AR curve.

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Added a comment about feature New Rocky Mountain Flatline Nearing Production? 8/18/2014 11:13 AM
C50

Recently, horst-link and split pivot designers have been implementing designs that allow for more heavily manipulated anti-rise curves that partially govern suspension behaviour while braking e.g. the new Ghost and Transition trail bikes as well as the new Salsa split pivots and the Devinci Spartan. This bike will have a lot in common with that design approach - the rearward slope of the rocker link is the clue. Expect RM to make lots of claims about braking traction. The traction benefits of this or that suspension parameter are hard to prove but many good designers seem to consider the rising AR curve that results from appropriately positioned linkage pivots to be good for braking performance.

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Added a comment about feature First Look: Radical New 2015 Specialized S-Works Demo Carbon 8/14/2014 8:32 AM
C50

Two articles, one on this site (http://www.vitalmtb.com/product/feature/Details-Unveiled-First-Look-2015-Specialiized-Demo-Carbon-650b,276) and one elsewhere (http://www.pinkbike.com/news/specialized-demo-2015-troy-brosnan-tech.html) confirm the substance of my earlier comments - things I supposedly couldn't know according to some. (note: I am not saying these writers share my opinions about the new Demo, they don't, only that they give the same account of the facts about the kinematics and structural features of the bike.)

This siite - http://linkagedesign.blogspot.com.es - helps give genuine information about how the linkages of real bikes work. You can know plenty about how a bike rides without riding it. The alternative is to believe the fields of design and engineering are a waste of time.

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Added a comment about feature First Look: Radical New 2015 Specialized S-Works Demo Carbon 7/30/2014 10:08 PM
C50

By the way, I didn't determine anything from watching the video. I used the geometric method of calculating anti-squat and anti-rise from the perfectly good photograph on this page. I had already looked at the dynamics of this sort of linkage from an emulation I tinkered with in the Linkage program quite some time ago. As it happens there is now a carefully developed emulation of the new Demo by Kryatof Jetmar that sits permanently in the public domain library of Linkage and it confirms the points I made about the new linkage function, although while the new bike is more pedaling neutral the improvement is modest rather than great. With the new details that are available our understanding of how the suspension functions will get more accurate but the general picture is already clear.

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Added a comment about feature First Look: Radical New 2015 Specialized S-Works Demo Carbon 7/30/2014 2:37 PM
C50

There is nothing arrogant in my comments. It has all been common design practice up until now. Look closely at the image you have made reference to. Imagine pulling the axle out and moving your arm forward in the open space between the two sides of the (multi-part) swingarm. You arm will go past two sets of pivots without cross bracing between the drive and non-drive sides before being obstructed by any sort of structure that joins the two sides of the swingarm. There would be very few bikes like that out there. That is because t is not a good idea to have too many pivots in the suspension linkage without proper cross bracing to create a stiff or flex free structure. Dual short link bikes commonly use full width pivot axles and Horst-links have always had a single piece seatstay that braces the seatstay/rocker pivot very effectively. Without much flex elsewhere and with the rear wheel axle also binding things together the unbraced chainstay pivot of the horst-link has worked well, without much flex, in practice. That you can move your arm around freely in this big void between the two sides of the swingarm of the new bike without finding any cross bracing near either of the mentioned pivots means that Specialized has thrown out the rulebook that everybody previously used. The point I have made is old school. From my standpoint (and I would say the standpoint of prevailing engineering practice) Specialized is violating a basic rule. No doubt, they would say, carbon changes everything.

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Added a comment about feature First Look: Radical New 2015 Specialized S-Works Demo Carbon 7/30/2014 12:37 PM
C50

The Yeti DH9 has been thoroughly analysed by Antonio Osuna (see http://linkagedesign.blogspot.com.es/2013/02/yeti-dh-9-2004-old-school.html) who notes the big difference that the little floating carrier makes. You are completely right about the carrier being crucial to the good braking performance of the Yeti and other similar bikes.

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Added a comment about feature First Look: Radical New 2015 Specialized S-Works Demo Carbon 7/30/2014 12:11 PM
C50

Sorry, my post was a bit of a moving target - ill considered expression, my bad. You were posting as I was editing. I was very interested to read your post though.

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Added a comment about feature First Look: Radical New 2015 Specialized S-Works Demo Carbon 7/30/2014 11:51 AM
C50

Yes, the suspension linkage on this bike has more in common with the Lawwill link than it does with Specialized's own expired Horst-link patent. "FSR" is by now little more than a marketing term.

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