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It really depends on where the flex occurs, it could effectively be a 6-bar with the correct flex.
Yeah, it does show it, yeah, it's obvious where the links rotate (counter rotating), I was interested in seeing some more travel happen to maybe see any inflection points in the movement. If I understand it correctly, Yeti's Switch Infinity, Ghost's dual short link, system, modern DW link layouts (four-bar), Yeti's 6-bar layout and maybe some more achieve good antisquat by extending the chainstay around the sag area, then through the inflection (one of the links starts moving in the opposite direction) the chainstay starts shortening, lowering the pedal kickback.
This is something that can't be done with a horst link but is something that might be possible with DWLink6 with a very similar layout to a horst link. That's why I wished we could have seen the complete travel. In the video they appear to cycle it riiight up to where the inflection point is and the links should start co-rotating (top link moving downwards).
Pretty sure this has to be Vittoria with some skin in the DH game now..? What you guys think?
It definitely IS vittoria, they did a nice closeup of the branding when Hugo Frixtalon finished with a puncture.
Considering the state of the world post-covid, I would be surprised if there WASN'T production issues. It's going to be years before we see consistent "normal" production cycles. It wouldn't be a bad thing if they let more of their athletes get a few events under their belts and report back before doing a full launch
Hmmm, looks like a proto Rock Shox Sid flight attendant on Nino's Scott.
About time! The sooner we can abandon cable lockouts, the better
Quick overview and demonstration of Suntour's new electronically controlled suspension system. Looke pretty dialed.
Looks to be a standard Mazza as far as tread goes. Last summer there was a vittoria rep and a sponsored rider at some eastern states cup races running Mazzas that had the same red hot patches. Kinda got the run around when I asked about them but can assume it’s just some slightly stickier rubber and maybe a bit of extra flat protection (for what it’s worth their enduro casing was pretty bulletproof to begin with compared to doubledown or supergravity) looks like every tire brand was having trouble keeping air in every riders tires at Lenzerheide.
Its definitely not a four bar linkage.
The chainstay is attached via two links are therefore has a virtual pivot point for where the "main pivot" would be, the seat stay will flex, meaning if anything, you could argue its a linkage driven "single pivot" where the single pivot is actualy a floating virtual pivot point.
🤯
Making it a linkage driven four bar.
Yeah my mistake, I was confusing the terminology of Horst Link and four bar.
Correct, it could be considered a virtual four bar system.
The big red hot patch was debuted on their new Syerra 'down country' tire (that is actually what they call it) which is their newest MTB tread. They also started releasing multiple casing options for tires though I didn't hear much news about it. The old ones were all 'TNT' branded but now their is heavier TLR casings (only available on 'race' tires, I think they are a softer compound) and 2-ply tubeless (closer to TLR weights but I believe still harder compounds). I can't find any real world pictures of the 'race' branded tires so it may be that is just the way they will brand those. Hopefully it is all a return to DH/Enduro for them as their road and gravel tire offerings have been pretty solid for a while.
On a (vain) side note, it is a bit unfortunate that the hot patch is so big and so red, that would be hard to match with certain bike/kit colour combos.
Not sure if this has been posted about the new Pivot DH bike
https://flowmountainbike.com/features/pivots-prototype-downhill-bike-ch…
So yea the pivot for sure needs flex somewhere in the system to unlock it. I did a suuuper rough model and measured the angle between the seat and chain stays at roughly bottom out (dont know shock specs) increases by around 0.3°. Where they're getting this I'm not sure. rear end looks like it built like a brick sh*thouse. (model not to scale).
They get it all over. A wishbone structure like they have here is not particularly stiff when you try to open it or close it. Adding a vertical brace makes it stiff (that's why triangles are so stiff).
The thing is unless there is some magic going on with the layup, the chainstay and seatstay both curve all along the length to achieve this change in angle. Which is likely coupled with optimisations in the geometry of the links to require as little flexing as possible going through the travel.
Yea makes sense. The frame will be flexing all over the place so not hard to imagine a 0.3°ish flex in the rear end. Definitely looks like the have laid out the hardpoints to minimise this figure as much as possible. Maybe also why they got rid of the vertical race compared to the non jack shaft bike?
Cool design though, I really like what it does with the axle path.
Here’s a nice pic of the links under compression
so is this a newer or older prototype version in these pictures than that radical one that's been raced? didn't have time to read the article.
What the high pivot bike is compared to a DWLink6 bike (the Athertons) is like what a flex stay single pivot (XC/Stumpjumper) bike is compared to a horst link.
The normal pivot height bike is a standard DW Link and thus has a vertical brace. It needs it, it wouldn't work otherwise.
@Sonofbovril2 shows the linkage in about the samepart of the travel (and not any further) than what the video showed. And I'd really prefer a video/animation to see where it flips over (if it does of course).
@krabo83 it appears they are more or less parallel to each other and were tested back to back in NZ.
What are the chances Jordan Williams is on the Demo Prototype at the next race? Kinda crazy that he beat both his teammates (and everyone else) on the "old" Demo. It's still incredible that all 3 specialized riders were in the top 5.
The demo he’s on is a custom size for him, I can’t see him jumping on the new frame design this season, he clearly has something that works for him. and the next race is this weekend….. so unless he has already been testing the new bike in the background, then I can’t see it happening. I also heard that even the prototype of the new frames work costly, not that would be a problem to a company like specialized. But Loic stuck to the old frame last season when Finn was already on it, to me that indicates that it must feel like a different bike to ride…. and getting to that level of speed and composure that Jordan show last weekend would have to be done on something you feel 100% confident on. (Only my opinion, could be wrong)
thx primoz! so they decided to go with the more complex one i guess? i admit, would be disappointed if pivot would opt for the more generic one as final version
edit: read the article, the complex one is the newest one, got it
on a sidenote, i think it's getting a bit ridiculous what's going on with bruni's bikes with all those hard covers and exaggerated secrecy, looks like they're hiding a motor there... finn's bike just has a cloth shroud which is normal IMO.
Makes sense, comfort on a bike can sometimes outweigh other performance upgrades to a frame/bike. To make the cliche F1 reference, lots of times when one driver gets an "upgrade package" for a race and their teammate is on the "old" package the teammate on the "old" package actually does better because they are used to the car.
Going back a few pages, on the Bikes & Big Ideas podcast, Franco Fratton (EXT’s founder) hinted that a dual crown MTB fork was coming.
Is there a new sram DH drivetrain that’s coming soon? Anybody have news on that stuff that I missed?
All this flex stay talk has me thinking about the tuning opportunities of flex stays. If the rear end is flexing as it moves through the travel range, then the rear end will behave like a spring.* This means a bike with flex stays will have an inherent spring rate, even without a rear shock attached. That is really funky behavior when compared to non-flex-stay bikes (traditional bikes?), where the frame movement is supposed to be as effortless as possible, and the spring rate is entirely controlled by the shock setup.
This probably wouldn't feel that different from a traditional bike. Imagine you took the shock off of a flex stay bike. If you stand next to the bike, and push the seat to cycle through the travel, you would feel the inherent spring rate of the frame pushing back on you, making it harder to reach full compression. It would feel the same as a traditional bike with a rear shock attached, except without any damping.
Let's do a little bit of spring talk for a second. Imagine you're holding a coil spring in your hands. You can compress it, and it will resist you, and if you pull it apart, it will resist you. Regardless of whether you compress it or extend it, it will want to return to a resting position. At its resting position, no forces are acting on the spring. If you push or pull the spring away from its resting position, you will feel the spring force. A flex stay will behave the same way. It has a resting position at which it wants to remain, and if you push it away from that resting position in any direction, it will impart a force on you to try and return to its resting position.
In the 2nd paragraph, we assumed that the flex stays were at rest when the bike was sitting at 0mm travel, and would begin to flex as you push into the suspension, creating the spring effect. But the rear end's resting position does not necessarily have to correspond to 0mm travel. So, a maybe more interesting angle on inherent spring rates: What happens when we play with the resting position of the rear end?
Let's say we have a 200mm flex stay bike and the rear end resting position is at 200mm travel, i.e. full bottom out. At 0-199mm travel, the rear end is flexed away from its resting position, and it wants to return to full bottom out. With no shock on the bike, the bike will rest at full bottom out.** With a shock attached, some amount of spring force from the shock is required to push the rear end back to 0mm. This means the inherent spring rate of the frame will act like a negative spring through the entire suspension travel. We've already seen negative springs used extensively in suspension products as a method of reducing stiction and creating a more plush feeling.
Another scenario is the rear end resting position corresponding to the sag point. Let's say our 200mm flex stay bike has a 65mm sag point, and the rear end resting position is also at 65mm. At 0-64mm in the travel, the inherent spring rate will try to suck the frame back up to the resting position. At 66-200mm in the travel, the inherent spring rate will try to push the frame back down to the resting position. This is where it gets really, really funky. Say our bike has a 500 lb/in coil spring on the shock, and the frame has a 50 lb/in inherent spring rate. At 0-64mm, the total spring rate will be 450 lb/in, and at 66-200mm travel, the total spring rate will be 550 lb/in. Theoretically, you can then achieve both a supple, low-spring-rate feeling off the top and a supportive, high-spring-rate feeling through the mid and end stroke without compromising one end of the travel for the other. For comparison, a traditional bike with a 500lb/in spring will have a 500 lb/in spring rate everywhere in its travel. If you want the traditional bike to be more supportive, it might be harsher off the top, and if you want it to be more supple, it might blow through the travel easier.***
All of these scenarios come with the caveat that I have no way of testing these theories or knowing whether or not they matter- if inherent spring rates are negligibly small, then all this becomes sorta moot. I just like speculatin'.
*Some people balk at the idea of a rigid body behaving like a spring. After all, springs are springs and rigid bodies are rigid, right? Well, yes, but actually, no. Intuitively, we understand that if you push anything hard enough, it will bend. If you're designing critical structures that encounter high forces like buildings or bridges, you need to be able to account for this sort of behavior. So, we can actually calculate rigid body stiffness. Its measured in force per unit distance (F/x) and denoted by the variable k. With the F/x relationship, we can know how far something will bend (x) if we put some force into it (F). Spring rate, the dominant characteristic of a spring's behavior, uses the same units of measurement and is denoted by the same variable. This is no accident- both rigid body stiffness and spring rate are measurements of the same exact behavior. The reason springs are springs is that rigid bodies will break if you push them too hard. Coil springs can be pushed really, really hard before they'll break, so they're more reliable. Plus, you can design a coil spring to have a really wide range of spring rates for a desired diameter and length, so they're more adaptable.
**This would actually be a huge pain in the butt, because the frame pushing on the shock all the time would make it really hard to get the shock on and off. To get around this, you could fully deflate an air shock, or use a coil compressor to squeeze a coil shock. probably not something you'd sell to consumers, but it's not out of the question for a World Cup mechanic to work on.
*** This gets complicated real fast, because we're not talking about leverage curves yet. Your ability to compress the shock by moving the rear wheel is dependent on both leverage ratio and spring rate. Usually, leverage ratios change with travel (hence leverage ratio being expressed as a curve, not a constant value) and spring rates are constant. Designers can use leverage curves to try and make the bike feel supple off the top and supportive deeper into the travel. On our flex stay bike, both leverage ratios and spring rates will change depending on travel. This could make it easier to achieve a magic feel, or way harder to separate the variables, making it difficult to tune and feel super weird.
All this flex stay talk has me wishing for some actual new product spy shots
doesnt the stumpjumper use a digressive damper tune to account for the spring rate of the flex stays?
On the DPS from Fox yes it does. Both comp and reb stacks