RideMonkey How To Series: Throwing a Tantrum in Public
That was my understanding as well, just like the frame of say a Transition Patrol is considered part of the 4 bar linkage.
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Right. I just would have labled the shorter bit attached to the chainstay since that dictates axle path more.
The other end and what you've got as #2 don't really from what I can tell. Those are just shock actuation.
I guess that top shock mount holds it all together though.
Nothing odd about that, just like a 4-bar is: 1, main-frame member; 2, shock linkage; 3 chainstay; 4, seatstay.
Standard convention.
Or more accurately, a specialized horst-link setup is an example of a 4-bar linkage, as there are 4 members. There are plenty of other examples.
wouldn't the point where the shock mounts to the downtube also be a pivot?
this is cool and all, but you've got a tough sell ahead of you. good luck, man.
this is cool and all, but you've got a tough sell ahead of you. good luck, man.
I think the "link" you are looking at that mounts to the top of the shock is actually two links, joined at the top of the shock, creating an actual pivot...
My head is spinning looking at this thing. Pinkbike should let Vernon Felton ride this. I feel like he is the most reliable bike reviewer going, besides maybe Kidwoo.
I'm still trying to grasp this claim
Because that's basically claiming two completely different leverage curves as it moves through its travel. So it behaves as red while pedaling, but as green/black while coasting? I thought it locked out then let loose, which was only at the top of the travel.....that would be one curve.
Shock needs to use the term 'floating shock actuation point' or I quit.
You can't have shit just attaching to nothing in space. That just makes no sense. It has to come from somewhere. God has a plan.
Thank you hmclay, you are correct. in classical physics and mechanisms, of which I claim to use the correct definitions for, it is a 6 bar linkage. In my haste to make it clear to the layman, I made the rookie mistake of not including the ground link (the frame), in my count. My humble apologies, consider crow eaten. I will correct this mistake in other forums.
The rest of your post is mostly accurate as well. The relative location of all the pivots is critical. Best case, great tuning potential for varying amounts of travel. Worst case, issues with production tolerances. I had to laugh when I read another engineer stating he designed everything to 0.1 mm. A particular manufacturer in Taiwan told me they hold their eye to eye shock length to 2 mm per frame. They make a lot of bikes for a lot of brands. They won't be making Tantrum. But the 0.1 mm you mention is not visible. 3rd decimal place stuff. About 0.5 mm is statistically noticeable, but even then, impossible to feel.
One advantage I have is the bolt in lower shock mount. It is actually reverse-able to change the position by up to 3 mm. Not as big a change as you might expect looking at the numbers, but a useful tuning option. I used it on the Tantrum Race (which I raced at the Sea Otter Enduro), to lower the bb, slacken HT and lessen the stiffening effect under pedaling, ever so slightly. In reality, I could've gotten similar results on the pedaling effect by running slightly more sag, but more risk of bottoming.
Further off than 2-3 mm (depending heavily on which direction) and things start getting off in a variety of ways, not the least of which is increased chance of contact from the SS bridge or tire at full travel, true of any bike.
So, yes, the position of the pivots is pretty damn important, but within normal manufacturing tolerance. The factory I use does final pivot machining after welding and heat treat, which offers superior alignment.
As for posting my exact leverage ratio, I will not. I have stated before, the devil is indeed in the details. If, in fact, the bike does what I say it does (no matter how many links), every bike company will be trying to figure out exactly why, patent or not. I can guarantee you many are doing just that right now, especially considering the very complementary review online elsewhere. That review is merely the first salvo. There will be more, and they will basically report the same thing, except the fork will be better.
The exact LR works in combination with the rising rate of the air can, the input of the Missing Link into the shock and the interaction of the vertical input from the wheel, via the rocker linkage. As you know, it's not too hard to backward engineer something. They will eventually model it correctly (when they get a bike). Until then, they (and you) can all spend time guessing.
Is this arrogant paranoia? Probably just smart protection of proprietary information as it applies to complex relationships between mechanical systems. I will say this. I have seen a graph posted that somebody made (vrock?) that was horribly off. About 38% off his graph was off the charts. And as a general rule, I'm not inclined to have any suspension design, much less one that uses an air shock, to drift much over 3:1. It simple gets tough to put enough air in for a heavy rider.
For reference, I will mention that at a recent Big Bear shuttle session, with an ex DH pro MTB hall of famer aboard, we used 220 psi for his 260 lb weight. super plush, no bottoming. He's not super fast anymore, but rides hard and we had room to spare. I weigh about 185 and run 165-170 psi.
I have also stated publically, that it is a falling rate in the first 40 percent of travel before becoming linear for the remainder. Fell free to speculate the curve in between. This allows a more instant bump response, especially when at full extension, when the falling rate is at it's highest. The rising rate of the air spring starts to provide a linear spring rate, even before the LR does. This provides a nice progressive cushion to catch the bike and prevent wallowing.
Then you are not a customer for this bike. I have stated before, if you don't care about pedaling performance or climbing ability, that eliminates one important reason to consider this bike. However, you may be surprised that there are advantages in DH situations as well, as the bump absorption is improved due to the instantaneous compression effect form the Missing Link. Enough to warrant the extra bearings in light of your maintenance requirements? Judgement call. You'd probably have to ride one to make that call.
You can disagree with my assertion that going downhill is easy from a design perspective, but there are tons of DH races won with simple single pivots and plain old horst link designs. Really, this is one of the most developed aspects of mtb suspension. The money and the conundrum, are spent on pedaling performance, for all but DH bikes. Even there, plenty of attention is paid.
If you took all of the pedaling performance enhancements out of your bike, that were designed in, you'd have to spend some time getting used to it before you liked it again, as you accepted the compromises of lost pedaling performance.
Not quite. A falling rate refers to the leverage, or motion ratio, from the wheel to the shock.
If it is a linear rate, neither rising nor falling, then the wheel would take the same amount of force to compress the shock at every increment through the travel. For example, 100 pounds per inch linear rate would take 100 pounds to compress the first inch, another 100 to compress the second inch and 100 more pounds to compress every inch till the end of travel.
If it is a falling rate, it would take 100 pounds to compress the first inch, then 95 pounds to compress the 2nd inch, and 90 pounds to compress the 3rd inch.
Conversely, a rising rate (which an air spring naturally has), would look more like 100 pounds for the first inch, 105 pounds for the second inch, etc.
Obviously, it's not notchy like that, as motion(or leverage) ratio curves tend to be curves, not notches.
So, by having a falling rate at the beginning of the travel, from full extension to about 40-50 percent, means that the wheel will be able to move a little farther for a given impact, because less force will be required to compress the next inch of shock stroke.
If you had a rising rate in that portion of travel, the wheel would have less movement before the force ramped up, so it would be harsher.
Later on in the travel, I want the rising rate. But not from the linkage. The natural rate of an air spring, when using a linear motion ratio, provides a perfect way to keep the bike from being too far in it's travel and prevent bottoming.
By using the term floating actuation point, we can determine that there is a confluence of them all interacting in a mutually beneficial manner. Better?I'm still trying to grasp this claim
Because that's basically claiming two completely different leverage curves as it moves through its travel. So it behaves as red while pedaling, but as green/black while coasting? I thought it locked out then let loose, which was only at the top of the travel.....that would be one curve.
Shock needs to use the term 'floating shock actuation point' or I quit.
It's not 2 leverage curves, but it is a combination of all forces acting on the suspension for varying conditions. The includes the stiffening/softening effect of the horizontal forces translated thru the Missing Link to the shock, as well as AS forces and the rising rate of the air spring. The difference between the red and green lines is the difference that occurs between max power and max bump.
You are correct, the locked out/let loose is only at the top of the travel, after the suspension has extended due to high climbing effort. It's not possible to do this on level ground without the front brake or a wall.
On level ground, you cannot create enough force to extend the shock, but you can create enough to make it feel like a hardtail while sprinting, staying firmly at static sag level. Then, the Missing Link still encourages the shock to easily compress upon encountering a bump, just at the lower sag level of shock extension.
We only want full extension when climbing, to give us more climbing oriented geo. The stiffness, basically, we want whenever there are no bumps (as long as we are pedaling). Another way of putting it is that the only time we need suspension is over bumps.
Or, floating actuation point.
The thing is falling rate also means you start with very low leverage. The big factor in making suspension supple is overcoming friction due to seals. That is especially true for air shocks. By using a low leverage rate you make it harder for the bike to overcome that. It is one of the reason most modern bikes are rising rate in the initial travel.
I'm not sure this is quite right. This may be why you want relatively high leverage early in the travel, because that would minimize seal and bushing friction, but being "progressive" early in the travel will amplify the fact that air-springs are progressive early in the travel (then flatten out, then go progressive again at the end). Progressive and high-leverage are two different things. In fact, going to a "falling rate" means you are using very little shaft travel for a given amount of wheel travel, usually high leverage. The ultimate in "going progressive" is achieving a 1:1 ratio, where things like seal drag and bushing friction would be maximized.
Perhaps you mean moving from a falling rate to a progressive rate, then I'm tracking. Really though, it would have to do with the leverage ratio (relatively high or low), not so much the curve, unless the curve was drastic.
Yes, fortunately Real World Cycles makes something you can buy for this.
Fair enough, an like others have said, innovation is cool (I mean shit, Specialized claims you will actually die without it) and I hope it works out for you. That said, my comment about designing a really good performing DH bike was intended to describe many of the nuanced factors involved such as wheel path, geometry, proper kinematics to mitigate wallowing/blowing through travel, etc...I think if you rode 10 different modern DH bikes back to back, you'd find most of them go about their business in meaningfully different ways. As for Steve Peat winning WC's on a Orange 222, that was a long time ago, when basically all DH sucked a lot of donkey dong. And ultimately, it usually has a lot more to do with the rider than the bike at that level. Hell, Ratboy won a WC race on tiny little bitch wheels 2 years ago
But I do agree you can make a righteously performing single pivot DH bike, like the GG/DH or TR500 for instance. But even then, I'd wager there's more subtleties than one might initially assume, albeit certainly less complex than a trail bike that requires better pedaling characteristics.
I have used progresive wrongly. A bad habbit since when talking in Polish people don't understand faling/rising rate. Rising rate would be a better term and that is what I meant.. It's not used to make it harder for your bike to go into travel but to overcome initial friction as you say. You want high leverage at the begining of the travel but not later in it therefore you get a rising rate.
But in the early part of the travel, when you've done almost no compression of the shock, the leverage ratio of the linkage is really not that important. Case in point: Nomad vs Capra have almost identical leverage curves past the sag point, but the nomad is the usual regressive-progressive of VPP, while the Capra is straight progressive and starts out with a much higher leverage ratio than the Nomad (3.3 vs 2.5, IIRC). The difference in breakaway force between the two comes down to who serviced their shock seals last.
You don't notice the rear wheel hanging on things on the nomad? Never hear a gigantic clack that comes out of nowhere as you're trucking along through some chatter?
Not to mention the insanely loose midstroke caused by that whole range around sag where the inflection point of the curve is?
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Yes, and yessssss!
Bike is so much quieter with a coil and doesn't squat like a ride paddy harvester anymore.
You can design linkages till the cows come home, but the best way to deal with climbing is to ride your bike more.
I think the end game here is a throttle and paved trails?
This is true to some extent. Although negative springs on air shocks have made that less of a concern than in years past.
I use the low leverage ratio to my advantage in the are between full extension and sag. At the top of the stroke, you are at the beginning of the spring force curve. On a coil spring shock with no preload, you would actually have zero spring force at full extension. An air shock will always have a starting spring force, but, it is always much less then the rider's static weight (otherwise there would be no sag). So when the missing link is at the top of it's travel, it will always want to naturally fall down into sag (unless sufficient pedal force exists). When the wheel strikes a bump, the combination of effects from the Missing Link's "knee" action, the instantaneous falling late and the initial low spring force, all combine to make a very plush response to bumps.
One more, important fact is at play. Essentially, the falling rate also applies to compression damping, effectively yielding a digressive compression damping. You may recall trek (and others) working with Penske shocks to develop that for mountain bikes. An advantage to my approach is that, in the reverse direction, as the shock extends rapidly toward topout, the rebound damping is progressive, so the suspension will start to slow down as it reaches full extension. The helps avoid rear end kick on jumps, etc.
I am not trying to take away anything from DH design. You will see my efforts on that some time in the near future. I'm a DHer at heart (translation, too slow for XC racing) and of course, think I can design a better DH bike as well.Fair enough, an like others have said, innovation is cool (I mean shit, Specialized claims you will actually die without it) and I hope it works out for you. That said, my comment about designing a really good performing DH bike was intended to describe many of the nuanced factors involved such as wheel path, geometry, proper kinematics to mitigate wallowing/blowing through travel, etc...I think if you rode 10 different modern DH bikes back to back, you'd find most of them go about their business in meaningfully different ways. As for Steve Peat winning WC's on a Orange 222, that was a long time ago, when basically all DH sucked a lot of donkey dong. And ultimately, it usually has a lot more to do with the rider than the bike at that level. Hell, Ratboy won a WC race on tiny little bitch wheels 2 years ago
But I do agree you can make a righteously performing single pivot DH bike, like the GG/DH or TR500 for instance. But even then, I'd wager there's more subtleties than one might initially assume, albeit certainly less complex than a trail bike that requires better pedaling characteristics.
But first things first. And trail bikes sell in much higher numbers. Which is, of course, why all the aforementioned time and money is spent on the pedaling performance by all the big brands. It IS the conundrum. How do you make suspension work only when you need it.? I have figured that out.