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Since tuned massed dampers are all the rage at World Champs this year, let's open up a forum topic dedicated to the subject. We'd seen a handful on the World Cup circuit prior to Worlds, but now they're everywhere. Some have hinted at them being used internally at the races for sometime, too.
Let's discuss what they do, how they work, where they could/should be used on a bike and if they're a viable product for gravity MTB applications.
Loris has one behind his BB, see it poking out below.
Im not even going to read the write up. Is this like adding a shake weight to the rear of my bike?
Ok, so after thinking about this a bit more (im not an engineer, my job is essentially playing with crayons) I would imagine that Loris's setup is much better than the mondraker one? Having something be on the complete back end of your bike would really mess with your rear shock.... right?
Ah crap read the other thread and I'm not even original. Lots of shake weight comments allready.
according to my 8 second long investigation (asking chat gpt...) the Mondraker approach is a bit unusual:
"Tuned mass dampers (TMDs) are more commonly used on the sprung mass of a vehicle. The sprung mass refers to the part of the vehicle that is supported by the suspension, which includes the body and any components attached to it. TMDs help to reduce vibrations and improve ride comfort by counteracting oscillations in the sprung mass, particularly at specific resonant frequencies.
While TMDs can theoretically be applied to the unsprung mass (such as wheels, tires, and suspension components), they are less commonly used in this context because the primary goal of suspension tuning is to control the behavior of the sprung mass to enhance ride quality and handling.
In summary, TMDs are more typically utilized on the sprung mass to address issues related to vibrations and resonance, improving overall vehicle dynamics."
Intuitively it doesn’t really make sense to me why you would want it on the unsprung part of your bike, when oscillations of the wheels is kinda the whole point of suspension. But fox does have a patent in the works that states the following: "by utilizing a TMD (tuned between 22-26 Hz) and mounted to the fork lower (e.g., an unsprung mass) the magnitude of the resonance peak is significantly decreased and the peak actually occurs at a lower frequency."
So Fox believes in its utility on the unsprung mass, and the top racers don’t seem to mind. Racers aren’t immune to the placebo effect, but fox does include some figures in their patent filing:
https://patents.google.com/patent/US20240229892A1/en
It depends on what vibrations you're trying to damp. If you're trying to damp the natural frequency of braking bumps, then I think mounting to the sprung mass is the clear pick. If you're trying to damp the natural frequency of the tires (tires are a largely undamped air spring), then mounting to the unsprung rear triangle would make sense. The seat tube is about 450 cm away from the rear axle, whereas the fork-mounted TMD is sitting almost directly inline with the front axle, so the front mount is in a much better position to damp suspension movement than a rear mount on the seat tube.
If you wanted to use a rear TMD to damp rear suspension movement and sprung mass, you'd almost want to construct an ugly triangular wheelie bar off the back of the bike to mount the TMD to, bolted onto the sprung mass of the main triangle. Obviously that's ugly as hell and no one's ever going to do it, so the Mondraker approach is an interesting alternative. Seems like Mondraker is damping front sprung mass and rear unsprung mass.
Springs in the Mondale rear have to be soooooo stiff. The wheel moves crazy fast.
So, just looking at the rear, this would be more used for counteracting large movements, right? Like when your rear hits a large square edge rock and it gets kicked up? Or do you think its more for small stuff like braking bump chatter? I couldn't imagine it working for small stuff? IDK.
Also do you think the one on the fox 40 has its own hsc and lsc clickers ;p
This is one thing I’ve been wondering about. To get say 1lb to have a natural frequency in the realm of braking bumps you need stupidly stiff springs. So stiff they are a little hard to find with meaningful amounts of deflection.
Interesting that they specify the range of 22-26Hz as that is right around the frequency I have measured myself as being relevant. The wheels natural frequency is close to, or just under that point but most suspension systems are effective up to about 15Hz then taper down to 20Hz, most stop responding around there but good ones appear to still work up to near 30Hz. This is mostly friction and a little bit of hysteresis in the damper preventing it from changing direction that quickly. So there is a narrow window just above 20Hz where the tyres will be bouncing and the suspension can't absorb it. This is one of the big reasons people need to run tyre pressures at the lower end of what you can get away with, or else you move that natural frequency further out of the range which the dampers can work. Once you get over that peak, the tyre will absorb most of the high frequency chatter but a mass damper soaking up those wheel vibrations could be very useful.
Using them on the sprung mass works in a different way, and could help with some vibration that makes its way through but typically they are used to damp out lower frequency oscillation. Ie an F1 car after it hits a kerb would bounce along for a while before settling so a TMD helps it return to normal much faster. On a push bike the rider can do this part themselves very well, as they are the bulk of the sprung mass but much more free to move than a car is.....a TMD on the frame or headtube would still have merit, I just guess that the optimum frequencies are probably more random and wider in range
I would think you could use some non-linear springs, like foam or a compressible fluid (air, oil, etc).
Also, just judging by the artwork on the Fox patent, that was an "oh crap, we need to patent something before everyone else"...
All the math involved is way over my head, but it sure seems like a lot of snake oil and extra weight for no reason. Maybe those who have ridden a bike with one can correct me...
What's the problem we're trying to solve here? Are the units designed to tune out vibration, or to allow the tires to touch dirt more often?
I've always wondered how/why the early 2000s Specialized Stumpjumper became the go-to bike in illustrations on patents like these.
Humans and bike suspension are both not so great at handling high frequency impacts. If you can reduce the amount of high frequency impacts that make it to your hands in particular, there’s some benefit. If I were to make an argument for buttercups it would revolve around this.
There is also some merit in making the sprung mass on your bike higher. Imagine a track where all impacts are 100 mm tall. If you make your bike VERY heavy, your ride height is set using preload on a lighter spring, and you’re running light damping, the wheels just move up and down under the sprung mass passing very little through to the rider. If you think this sounds like a car you wouldn’t be wrong haha. Obviously I’m not saying we should do this, but it’s an example taken to an extreme for the purpose of illustration.
On the note of patents, the drawings don’t really matter. It’s all in the claims. So not a ton of effort is put into the drawings sometimes.
This is a good point, the frequency of braking bumps and general rock chatter may be wildly different than say an extremely square edge but that’s liable to buck you forward. Depending on what the FMD is tuned to, it may have a big effect on kicky hits and minimal effect on everything else. It probably opens up a new way to optimize suspension tuning.
I’ve been running a CounterShox on my bike for a month or so. I’ve also tested in a motocross bike. On my DH bike I have one mounted to my seattube and fork. Heavier on the fork, lighter in the middle of the bike. Feels like a good balance from wheel to wheel.
The countershox is set up in a way that dampens square edge and braking bumps the most. Think sharp high frequency spikes.
Jumping the bike has less pop and is super stable off the lip. Really mellows out the kick.
There are negatives, on the fork it feels heavier side to side movement, on steep trails it can kind of “pull you down the hill”. Some suspension adjustments are needed. But overall for me it’s a positive addition to the bike, I enjoy the planted feel more than the bike deflecting on sharp bumps. Feels like much more tire contact and traction.
Allowing the tyre to stay in contact with the dirt. Thats the ultimate goal you always want....some comfort/reduced vibration is useful too for long runs/days but at any moment its mostly about consistent tyre grip as you only have as much grip as the lowest point of those fluctuations
As for extra weight - in everyone understands how increasing the sprung mass makes for a more comfortable/stable bike, and using a tuned mass damper should create a similar effect with a much lower weight penalty. Putting it at the axle is just moving it down a layer and closer to the contact patch, ie the wheel is its own spring/mass/damper system (just very little damping)
I imagine the TMD on the end of the chainstay is attempting to calm the additional small chatter from hits the suspension can't deal with. There's not much room inside of the damper to move so it's only going to be able to deal with movements inside the TMD's internal travel range.
I'm thinking like tires bouncing or the chatter of gripping/breaking grip during braking.
I think it could also help temper how much "overthrow" (an idea that I'm sure has a real word/phrase attached to it that I just don't know) the suspension has when hitting something that causes a large movement and the momentum carries the movement beyond where the suspension is attempting to hold the wheel (think hitting a square edge hard and the wheel bounces higher upwards off the edge losing some contact with the surface rather than staying in constant contact with the surface). If it could calm that stuff down we're looking at a lot more grip in a lot more critical "just after impact" moments.
So true! There must be some stock image site patent lawyers pull from. I could see that image being labeled "modern mountain bike" 😂
True, claims are what matter, but the images can be an decent indication if it's an actual product in the pipeline or some brainstorming ideas they are looking to protect until they have a project for them. This seems like the latter.
@carlinojoevideo do you notice any steering/lean weirdness with the fork mass offset from centerline?
Belleville spring stack?
all this voodoo is brand new to me, so here are some possibly dumb questions.
would there ever be a need/benefit to using them in a horizontal way? like inside a rear hub/axle to ease a rear end getting kicked out/deflection? could you use them like bar ends parallel to ground (or head angle?) as a steering damper? ignoring weight, would these things help an XC bike feel more stable down the hill with light tires?
those old bontrager buzzkill things mentioned in the tech forum are interesting too, but @NoahColorado has dibs on 'em.
Let’s get down to brass tacks. Fully rigid bike with TMDs vertically on the front and rear and in both hubs horizontally
Do you have any data, or knowledge, on how casing construction, rubber durometer, or inserts affects the tire frequency? I would imagine it could shift things a similar amount as air pressure on its own, but I really have no idea.
I do think that there likely is a measurable effect because some tires generally feel more “dead” than others and the same tire definitely feels more dead in colder winter temperatures.
@whitesq - offset left or right a few inches doesn’t change the feel for me. Just general lean weight is felt when transferring in berm to berm. But it’s something I got used to.
@Spomer. There could be use horizontal, but personally I don’t like it would have a big enough change to make it worth the weight. Not like on a motocross bike where the rear gets kicked left or right in ruts. I don’t think this happening on DH often.
I think it could help XC bike for sure, but can’t imagine them ever adding weights, the time they’d gain in descent they might lose on climbing
Surely the gyroscopic effect of two heavy wheels is enough to stabilize and resist tilting?
Or are we going hard and just putting a damper on everything
who makes them that you use? its an interesting concept and definitely new to ME. be cool to read up more
https://countershox.com/
Yeah thats a long term project I am slowly collecting data on....there is a huge difference between casing and compounds. Measuring the force vs displacement curves tells you the change in spring rate and damping from different rubber, and changing spring rate will have a proportional change to frequency
Blue line is a Conti Kryptotal DH tyre (note:29") at 23 and 25psi
Red line Maxxis DH maxx grip 2.4 x 27.5"@ 23psi
Yellow line Maxxis EXO Maxx Terra 2.4x27.5" @ 26psi
The gap between the lines is an indication of damping, the EXO has a softer rate and less damping, while the Conti is much stiffer for a given pressure.
@sspomer - rotational mass dampers/inertial dampers are a thing, can't remember the kinds of applications but they exist in different forms. Different to inerters which is another thing that will come up when you google TMD's!
This diagram (taken from Analysis techniques for racecar data acquisition by Jorge Segers) shows the level of vibration passed through when comparing 2 parts of the system (it is simplified for theoretical purposes). 1 on the y-axis means the size/displacement of the vibration output is equal to the input (ie rolling slowly over a large bump, the vehicle rises the same amount as the wheel). A value greater than one happens around the natural frequency where the input gets amplified (movement at the chassis is larger than the bump).
Red line = body of the vehicle bouncing on the suspension (your sprung mass natural frequency). This is the section the famous renault F1 cars were targeting
Blue line = how much the wheel moves relative the ground inputs, ie the suspenison movement
Black line = tyre movement between the rim and ground, the point which a hub mounted TMD would act
These follow very similar trends to what I described above in push bikes - the exact frequencies aren't the same but pretty similar. The peak of the tyre is around 20Hz as well, where the suspension is below one (not amplifying bumps) but hasn't dropped away completely, but if those lines were to shift away from each other you would have much more vibration transferred to the vehicle
Thank you!
Some more info I found when I was digging into what the mass dampers do.
https://countershox.com/elements/pages/blog/
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