After an incredible finish to 2015 in Andorra where Bruni earned the right to rainbow stripe his garments for the rest of his career, 2016 was looking spectacular for the 22-year-old French rider. He qualified 1st in Lourdes, only to crash out in the final with the green light well and truly on, this was remedied in Cairns where authority was stamped with his first World Cup win. Unfortunately Loic's hopes of domination this season are over after a multi-break collarbone injury in training this week that will put him out of Fort William, Leogang, and Crankworx in France. I'm definitely not counting him out of another gold medal on the legendary Italian hillside in September.
MENTIONS: @Specialized
But somebody crashing on a Demo comes as no big surprise considering the new Demo has the most unstable rear suspension design out there due to the much-to-low concentric BB pivot. I've already previously documented how having the wheels moving in exact opposite directions compromises traction and increases instability, and those facts have gone completely unchallenged even by the guy who actually designed the bike.
Before you cuss at me, call me a troll, or tell me I'm wrong, I have one simple request: Show me a current DH bike with a more unstable wheelbase than the new Demo. Good luck with that one, haters.
Heal up Bruni!
I noticed you didn't come up with another DH bike that is more unstable, thanks for the frustrated confirmation of my assertions about the new Demo.
I absolutely blame the injury on the Demo, it only stands to reason that if you are on an unstable bike you are more likely to go over the bars and become injured. Low c.o.g. but o.t.b.
Specialized: please kill the new Demo before it kills someone.
I noticed you also couldn't think of another current DH bike with a more unstable suspension design, thanks for the confirmation about the instability of the Demo.
You ask: "What are you trying to do with all this information Protour? why rabidly pursue this, what good can come of it?"
Safer bikes for all my two-wheeled brothers and sisters.
This is about Bruni's healing not your theories. This type of article is where we MTBers unite to wish someone a speedy recovery not start pointing fingers at equipment.
The logic of your statement presents the idea that regardless of how unstable a bike is, riders are going to crash sometimes anyways, so the stability of a design has no influence ever over whether somebody crashes or not.
And you said I was mental?
www.vitalmtb.com/forums/The-Hub,2/Loic-Bruni-Breaks-Collarbone-Will-Miss-Several-Races,9209
The fact-based evidence is that nobody in the world can point to a current DH bike with a more unstable wheelbase. That's pretty convincing.
I blame the crash on the Demo because it is an unstable design that increases the chances of crashing and injury. A DH bike with the most unstable wheelbase in the history of DH bikes deserves this negative attention.
I feel bad for Bruni's injury but I'm not going to let his sponsor off the hook. This is the best time to bring attention to this, similar to how some auto crashes reveal product defects that caused injury. I hope Bruni reads this and wonders why nobody can come up with another DH bike that is more unstable.
Oh come one, men, you just killed the demo class action boot camp...
Maybe should we go on with the Enduro conspiracy ?
Ok, just a hint : maybe Loïc crashed on the new Enduro prototype, the one with concentric bottom bracket pivot ?
He was on the Demo when he crashed in the first World Cup race of the season that he should have won.
As long as nobody can name a current DH bike that is more unstable than the new Demo, my efforts towards making the sport safer are justified. People telling me to shut up about the unsafe design of the Demo are essentially like people who think it's ok to ride without helmets and don't want anything said about it. Just because you ride a Demo and Specialized is your favorite brand doesn't excuse the company from criticism over what is very clearly an unsafe design.
Can you think of a bike with a more unstable wheelbase?
The position of the pivot around the BB, versus being above, below, behind or ahead will only slightly change the length of the lever, and therefore the path of the arc. The concentric BB simply allows for a lower center of gravity, something which nearly all manufacturers are trying to achieve with their bikes.
Again, I would be very interested to see the calculations you have performed in determining the Demo 8 to be "the most unstable rear suspension design" The Iron Horse Sunday, with its near vertical wheel path was controversial in its time, and called for a dramatically different riding style to master, yet Sam Hill managed to be quite successful aboard it, and I don't recall anyone ever saying it was "unstable" or unsafe!
looking forward to hearing your empirical evidence on this subject.
What makes the Demo unstable is that the wheels are moving in nearly opposite directions, when examining the axle paths.
At the very least it compromises traction when using your brakes and makes your front tire more likely to break loose. The radically changing wheelbase also makes the bike unstable through rocwheelbase, making an OTB more likely.
Decent theory, but the concentric bb pivot actually wouldn't have as of a negative effect on a trail bike because of the steeper headtube and reduced suspension travel.
I don't think that our sport is as the point where we can confidently say that any suspension is design is superior to another. The Pro's have shown that any number of different bikes can make it to the top step of the podium. I think Aaron Gwin has proven just that. He has won aboard Trek, Specialized and YT, all of which are bikes that exhibit an arcing forward wheel path, which, if I understand correctly, is the main reason you claim the Demo 8 is an unstable design?
Okay, I just ask to believe you.
But IMO, if I listen to you (I know I shouldn't ;-)), all bikes, including motorbikes, are unstable for the same reason, i.e., front axle moving rearward due to fork compression, rear axle moving frontward when becoming higher than main pivot level.
Can you provide us with a comparative study of wheelbase shortening between SAG and full travel (incl. fork effect i.e. function of head angle and fork travel) between different dh bikes, and then quantify how much more shortening the demo undertake in comparison to other bikes?
And in fine if there is a % difference, can you demonstrate a significative (quantifiable) effect of this % difference on bike handling vs. the benefit of a lower CG ?
Good luck, Mr Phelps.
There's no such as "perfect" bike in this world.
Oh wait a minute.....
It actually exist.
MAKE YOUR OWN "PERFECT" BIKE!!!!
You probably had a little crash when you OWNED A DEMO 8 YOURSELF at some point, and can't cope with the fact that it's your f*cking fault you crashed. Deal with it.
1) The concentric bb pivot on the demo is indeed very low. However so is the pivot near the dropout, meaning the axle path will actually be very similar to most other FSR or single pivot dh designs out there, barring those with particularly high main pivots. The Trek session for example, which is widely regarded as one of the best all round race bikes should (without actually looking at any real numbers) produce a similar axle path.
2) The axles moving in opposite directions isnt necessarily a bad thing. Yes the wheelbase shrinks, but at least the riders CoG will remain fairly central. On bikes with very rearward axle paths (high main pivots) the rear end grows while the front end shrinks. This causes the riders CoG to effectively move much further forward very quickly, leading to unweighting the rear while and applying all that weight to the front. In my head this is going to cause much more of a problem as the rider has to move their weight around to compensate rather than just staying central and dealing with a momentary shortening of the wheelbase..
@protour is a special one
Where does that say the Demo suspension is the most unstable?
Of course it does. But the rear wheel moving in nearly the exact opposite direction, as on the Demo, creates a wheelbase that changes more than any other bike.
Thanks for all the compliments, and nice to see all that nobody could come up with a DH bike with more wheelbase instability. Perhaps this wasn't the ideal time to bring up the criticism of suspension design, and I hope Loic's has an effective recovery.
None of us know why Loic crashed. But I have to say that the axle path on the Specialized bikes, or pretty much all low pivot bikes sucks. I have owned few Specialized bikes. Vertical to forward arcing axle paths suck at bump absorption and do create instability especially on a DH bike.
But since just about all the bikes on the WC are very close in axle paths, they are all riding on par as far as that goes, except for the Commencal DH V4.
Until you have ridden a higher pivot, you won't know what Protour is speaking of.
Couldn't help myself. Probablym are him all the more determined to hold onto the rainbow stripes.
Yes it is important to get a good leverage ratio. You can get the frame to swingarm plenty stiff. But once you have ridden a significantly higher pivot bike, you see the night and day difference. And it is probably safe to say most people on here have not ridden one.
You do have the lengthening of your wheelbase on a high pivot bike, which is a positive at giving you better stability, but is something in tight turns you may have to adjust too (and usually in tight turns you are not deep in the travel anyways). The positives far out weigh the negatives for this type of riding.
Depends what you define as a "normal" person. Any sane person with common sense will know what is publicly acceptable to say. Also I didn't "attack" anyone so calm down, everyone misreads stuff said over the interwebs. No need for everyone to get triggered over a guy thinking he knows something we dont.
I honestly dont know if protour is trolling everyone or not but either way I have my popcorn out because this is damn good bed time reading.
It's a family we have here, I love you guys :..(
I very rarely wade into Internet sh*tstorms like this but the laws of physics and geometry would like a word...
Your argument on a concentric pivot greatly shortening wheelbase works....if the chainstay is completely level with the BB, and the chainstay is directly attached to the rear axle. If that's the case the axle has no where to go but forward, creating instability. There's a problem with that argument with the current Demo, it has neither of those attributes.
The chainstay is sloped twords the ground on the demo significantly, AND there is a pivot at that low point. This in conjunction with the axle being a significant height above that pivot BEHIND that pivot may actually move that axle path reaward initially, or at bare minimum in a vertical manner. Because as that chainstay rises when the bike hits a bump, the seatstay linkage will acually rock the axle to the rear of the bike because of the dramatic negative slope of the chainstay becoming level as it goes through its travel.
I'm eyeballing it here, as I don't have a demo sitting in front of me with the shock off, but I can't see how it would work any other way.
However, someone did link a chart showing that despite the extremely low position of the Horst link, the new demo has less rearward travel than the demo that came before it by about a centimeter. The link had a graph showing chain growth against rear travel, and the new demo had the least reward movement of the major brands shown (I forget what they all were).
My conclusion is that yes, the new demo has rearward movement and chain growth but much less than other bikes. I would strongly prefer more, and while its not going to send everyone over the bars like Protour claims, it does probably get hung up incrementally more in the rough stuff than a higher pivot bike. Gwin and Bruni can can handle it because they run so much compression and very slow rebound, but us mere mortals would be better served by something with more rearward movement.
It does show a fairly vertical axle path.
I agree that it's not terrible, but that I would rather have a bike with a little more rearward path. Though according to Joe Graney from Santa Cruz, axle path isn't really important anymore: www.santacruzbicycles.com/en/us/news/344
www.google.ca/search?q=ccm+downhill+bikes&safe=strict&client=ms-android-bell-ca&source=android-browser&source=lnms&tbm=isch&sa=X&ved=0ahUKEwjs08We8vjMAhUP4GMKHZ9YDWMQ_AUIBw#imgrc=6S-Bzr7RO87s_M%3A
This what you're looking for?
Ride a Canfiel Jedi, Commencal DH V4, Zerode, or one of our bikes, and you will see a big difference in how axle path can effect the way your bike responds to bump absorption.
Even for a 4 inch travel bike with an axle path of a high pivot (like our bike, the old Balfa 9, Zerode), you would notice a big difference in bump absorption ability. Now would everyone care to have it, no. But if you are a rider who like to ride fast and hard even when you are on a smaller travel rig, you would proboably appreciate having that bump absorption. Besides the fact that it allows your rear rim to take less of a beating.
There is no current larger bike company offering anything of any significance in terms or rearward travel. To get the benefits, you have to have it high enough to where you have to run an idle gear. And maybe Joe was refering to that situation of trying to have some minute amount of rearward travel at the begining of the arc.
Commencal isn't small.
You are correct that there are tradeoffs between the two. I personally have not felt that the cornering ability of my high pivot set up is a glaring issue. Before i even rode a high pivot bike these were some of the negatives you hear people talk about. I have found I can rail a berm just as fast. You just learn to position your body weight maybe a little differently.
I do not claim that a high pivot bike is going to make you 10x faster. But it will improve your personal bests simply because they rollover terrain quicker with less resistance, easy proven physics. Isn't this the argument for bigger wheels? And there are tradeoffs to that too isn't there? Bigger wheel may roll over stuff quicker, but they are heavier, not as strong, less agile. So you as a rider pick what you want to deal with.
I would rather ride a 26" high pivot, than a 27.5 or 29" low pivot. The 26" high pivot rolls over hits better than a bigger well low pivot. I have experienced it.
Take your time and heal up properly Loic, your destiny will wait ☺️
Back in the day, all MX racers were sporting the latest in chest, arm, knee and shin protection. Like football padding but light, breathable and super high tech. I had a mesh suspended plastic shoulder pad absolutely save me from a broken collarbone. Because I almost broke it.. Almost every full contact sport is armored up mostly to protect them from another guy- that's completely armoured up.
We go cartwheeling down canyons at speed with nothing more than the latest jersey... I don't get it. At least for DH.
ExMxEr.
STILL GUTTED from losing Stevie.
can't wait to see you back at it!
@Protour:
with all due respect, your stability theory is extraordinarily simplified, and personally I believe a bit of a red herring.
nearly all bikes (with the exception of the canfield and similar, have forward sloping wheel paths. While true the demo is the most extreme of the common bikes (demo, v10, gambler, devinci). It is only some 8mm more, over 208-213mm of rear wheel travel. with this in mind, what specific reason do you say the demo is "unstable"? in what circumstances do you believe it would be unfavorable or "unstable"
I believe it would be more prudent to analyze the weight shift as a function of wheel travel. as to reduce weight transfer forward or backwards when compressed. with that in mind the rear wheel should move forward as a proportion to COM location, to the front wheel move moving backwards. forinstance: I personally ride a weight distribution of about 67% on the rear. the fork moves 112mm rearward. so to maintain that percentage when compressed, the rear wheel has to move forward about 55mm (where the demo moves 37.25mm). The demo would have a weight transfer of about 1% while a v10 would be 3%. a canfield would be 7.5%
the idea that the stability of a bicycle would be a function of any single parameter is obtuse even for extremely simplified vehicle stability analysis. when we are incorporate wheel path, IC, CC, anti-squat, anti-dive, brake forces, chain forces, damping, spring forces as well as human input we are looking at unsolvable nonlinear partial differential equations.
Prompt rétablissement.
Failed ,,repeat the year.
You sir.
Are a bag of floppy dicks.
goo.gl/Bb0hOV