Tuned Mass Damper for your steerer tube

Pretty interesting thing Rimpact is currently developing.

If you start here https://www.instagram.com/p/CrAlddStIjs/ and navigate left to newer posts, they’ve written some explanations and have more photos.

There’s a really big one of those in the Taipei 101 tower.

Lots of info https://bikerumor.com/rimpact-is-developing-a-tuned-mass-damper-for-mountain-bikes/

I’m initially skeptical that such a small thing could make a difference, but the Taipei one is only 660 tonnes.

Well it worked for Alonso when he drove for Renault, that wasn’t exactly big either.

Whether or not these are things are beneficial or make it into production, that folks are working on stuff like this is super cool

I woke up at 3:30am thinking about this!

Rimpact has increased the density of materials to tungsten, I couldn’t remember if it stated the weight of the dampener but have just checked the article again and it states 204grams. The steel version was 79g.

So it looks like a heavier dampener is better than lighter but is constrained by the dimensions of the steerer tube hence increased density of materials.

Is this not a case of the increase between unsprung Vs spring weight rather than the action of the dampener weight being suspended/sprung? Especially as the weight is being added in the same plane as the forks.

It would be interesting to see a 3rd set of data with the dampening weight fixed/static for comparison.

IIRC Mojo/Chris Porter experimented with lead weights at Fort William to change sprung Vs unsprung weights.

I’m waiting for the osmium version.

Would be interesting to see how it works on rigid fork – gravel application.

Would be interesting to see how it works on rigid fork – gravel application.

Its effectively making the suspension work ‘better’ (I’m guessing it would overcome the fork seal stiction) by momentarily resisting the movement of the steerer/unsprung mass. In a rigid fork it would cause the front tyre to deform more over the obstacle as the fork is momentarily less willing to move. I think?

Could this be combined with a steerer toolkit, whereby the tools are incorporated into the mass?

Same principal but different in application to the old Bontrager harmonic damper bar end plugs?

For a similar weight penalty you can have dual crown forks and have much better suspension.

To be honest I love their tyre inserts and I feel like you get the desired effect from them already. It’s like turning down the volume on trail chatter.

This looks like something you could throw together in the garage out of curiosity. I believe that you might be able to feel it doing ‘something’ but I’m very sceptical that this thing alone is going to make anyone faster.

Could this be combined with a steerer toolkit, whereby the tools are incorporated into the mass?

Imagine how reasonably priced that would be 😀

For a similar weight penalty you can have dual crown forks and have much better suspension.

An interesting point, re. what you could “buy” for the same weight gain. A coil conversion would be an interesting point of comparison too. My experience is that coil forks have always given me more comfort and control.

A coil conversion would be an interesting point of comparison too

Coils are betterer as they don’t require the sealing element of the air spring. That seal is forced against the shaft by the pressure of the air spring and needs a certain amount of force to overcome the stiction and get the fork moving. My fuzzy brain logic is thinking the mass damper is creating enough resistance / momentary sprung mass to overcome this oil seal stiction hence the improved feel/performance albeit at a 200g weight penalty.

Dual crowns don’t make any difference in this instance, they track better but the initial stiction is the same.

Dual crowns have far less chassis stiction.

I’m sure Vorsprung claim that 50% of air fork friction comes from the air side seals, so about the same as is achieved by the damper.

Coils are betterer as they don’t require the sealing element of the air spring. That seal is forced against the shaft by the pressure of the air spring and needs a certain amount of force to overcome the stiction and get the fork moving.

And that stiction doesn’t really get worse in between lowers services, in the way that air fork performance does.

Oooh, interesting. Dynastar and Rossignol had similar tech in their skis about 30 years ago. Dynastar had a free lead(?) mass suspended between some open cell elastomers and rossignol had heavy wibbly wobbly tips made of some rubbery material. I had one of the dynastar units for a project I was working on. If you shook it it felt really weird like it was actively trying to work against you.

I wonder if you included a nice powerful rare earth magnet in the mass, would you get it to induce eddy currents in the steerer and then self-damp?

Is this not a case of the increase between unsprung Vs spring weight rather than the action of the dampener weight being suspended/sprung? Especially as the weight is being added in the same plane as the forks.

The BikeRumour article does mention placebo comparisons.  I assume that must have been done with a static mass of the same weight?

I guess we’ll be seeing them at DH races before too long (assuming they’re not already being used).  The good thing about non-dropper posts is you can easily fit one in the seat tube as well…

I wonder if you included a nice powerful rare earth magnet in the mass, would you get it to induce eddy currents in the steerer and then self-damp?

Nah, but it would give you a boost like Mario Kart on an eBike…

IIRC Mojo/Chris Porter experimented with lead weights at Fort William to change sprung Vs unsprung weights.

Loads of people have weights strapped into the BB areas of their DH bikes. You can see them on all the bike spotting articles around world cup time.

It’s coming this summer https://www.instagram.com/p/C5_MRZbMFQ5/

I honestly have no idea of how this thing works.

Stem is bolted tight to the steerer. so what does having a springy thing inside the steerer do ?

I honestly have no idea of how this thing works.

Stem is bolted tight to the steerer. so what does having a springy thing inside the steerer do ?

Renault used them on their F1 car back when Alonso won two championships with them (but then they were banned on the grounds that they were a movable aerodynamic device). Basically it was a weight suspended between two springs placed in the nose of the car. When a front wheel hit a bump, it would compress the main suspension spring which would then try to force the front of the car upwards. The tuned mass damper opposed this because the weight would try to stay immobile due to inertia, so it would compress the lower spring, which opposed the force from the main suspension spring. This stabilized the car over bumps and improved the aerodynamic performance. F1 aerodynamics are extremely sensitive to ride height so all the teams had to pour money into researching tuned mass dampers. They were outlawed basically as a cost cutting measure, the “moveable aerodynamic device” was just a way to justify the ban.

I’m skeptical about how much benefit they will provide to a mountain bike but willing to be persuaded. The same as with an F1 car, the weight and springs would need to be tuned to the individual rider, bike, and course in order to get maximum benefit.

https://www.formula1-dictionary.net/mass_damper.html

From what I can see this is more about controlling vibrations than anything else. The springs on that vid are wound too tight to allow a lot of actual movement, and whilst there’s a benefit to weight in the stem area to improve the ratio of unsprung mass, a spring mass is less effective at doing this than a dead weight strapped to the frame. So think of it as having the same affect as vibracore bars, through a different mechanism

I’m skeptical about how much benefit they will provide to a mountain bike

Shouldn’t be too hard to determine.  Two identical bikes, one with, one without and a variety of testers, including some average riders not attuned to identifying subtle nuances of different riding performance.  I wonder if Rimpact would be brave enough to submit to such a test

If only there was a magazine…. 😜

Could this be combined with a steerer toolkit, whereby the tools are incorporated into the mass?

The tools would certainly have a nice heft to them, tungsten allen keys and chain tool…

These are very common in the automotive world, but usually held by an elastomer spring rather than a coil. See them on diffs, gearboxes, shifter linkages etc.

Vibration damper bar end plugs seem pretty common on motorbikes. Probably not common on on bikes since MTB bar vibrations aren’t likely to be as constant as they could be on road surfaces, plus weight weenieism in road cycling.

From what I can see this is more about controlling vibrations than anything else

This. The mass and spring rates would be tuned to target specific frequencies that they wish to reduce the amplitude of.

jameso
Full Member

Vibration damper bar end plugs seem pretty common on motorbikes.

Yep, but that’s usually just mass loading, static weights. Can make a surprising difference though, I (like everyone else with my era of subaru) took off the massive steel bar ends because they were bloody hideous, but I had to admit they were there for a reason. But if you asked me “can 50g of steel make much difference on a 160kg bike with like 12kg of wheel and tyre and however much suspension travel etc” I’d have probably said no. Especiall when literally the same parts turned up on multiple bikes, so I thought how can this be tuned?

“These are very common in the automotive world, but usually held by an elastomer spring rather than a coil. See them on diffs, gearboxes, shifter linkages etc”

2CVs suspension system, in the boot of Porsche convertibles, ends of crankshafts etc.

Can’t think what the price will be, with their simple but clever and nicely made in the UK BB stand being £130 https://www.rimpactmtb.com/stand

Some of the motorbike bar plugs use a mass with an elastomer between it and the bar so I’d assumed they were using a similar principle, and wondered if they’d make much difference on a bike.

2CVs suspension system, in the boot of Porsche convertibles, ends of crankshafts etc.

It’s also essentially what a DMF is as well.

4 part blog series up on the website now about the development

https://www.rimpactmtb.com/blog-1

Now Fox are in on TMDs, with a patent too

https://www.pinkbike.com/news/fox-are-developing-a-tuned-mass-damper-for-mountain-bikes.html

This type of device has been showing up on DH bikes in various locations.

Here’s a demo of the effect on a wheel https://www.instagram.com/p/C_wFh6QRTRR/