Truth or hype: Zertz inserts?

[alexedge]

Just bought a new aluminum frame, love the feel of aluminum the way it rides, accelerates, everything except the slight road buzz. In my experience, carbon or Ti seatpost typically transmit slightly less of this vibration to your backside than an aluminum post, so I'm in the market for a new seatpost.

My question is, do the Specialized seatposts with the Zertz 'vibration damping' inserts really make a difference? Not looking to start a "Specialized rocks!/Specialized is the Evil Empire" argument here - please only reply if you have personal experience with using both a standard (non-zertz) seatpost and a specialized post.

Thanks!

[Skeleton]

I recently bought a Cervelo R3, but was considering a Specialized Tarmac during my shopping. The Tarmac had those Zertz inserts on both the stays and the seat post. At first I was intrigued, but then brushed them off after considering their potential from an engineering perspective.

I am a structural engineer; as such I occasionally design building frames with dampening systems incorporated, when in a seismic region. The principles of dampening on a bike really aren't much different than dampening against seismic motion in a building. Anyway, as I see it, here is the gist of it:

Dampers work substantially to gradually absorb vibrational energy when the input energy is unsustained. Consider a shock briefly applied to a bike frame; a very resilient and stiff material like aluminum can allow the frame to continue its vibration for an extended period of time after the shock (riding over a bump) ends. When a dampener is introduced in the system, that device will gradually absorb the energy and cause the vibration to more quickly diminish. A good example would be to contrast how long a tuning fork can sustain its free vibration between the case of unbraced and braced ends (ie: touching the vibrating middle with your finger, which acts as the dampener - this is akin to the zerts inserts).

However, dampeners don't do much if the input energy is continuous. Well, such is the case of rough road surfaces and repeating road ripples. Frankly, I am not too concerned as a cyclist with infrequent unsustained shocks, such as from dips in the road - I just lift my seat and ride through or around them.

In short, I think the zertz inserts are a marketing ploy. Specialized has exploited a scientific principle that probably has little impact on the performance of the frame. In fact, their inclusion might do more harm by introducing a weak point in the strength of the frame, etc.

[LWaB]

Good to see another structural engineer (I was previously). Australian and British terminology tends to be that dampening involves water, damping involves vibration. Do the Americans not use damping?

[Vireo]

I recently bought a Cervelo R3, but was considering a Specialized Tarmac during my shopping. The Tarmac had those Zertz inserts on both the stays and the seat post. At first I was intrigued, but then brushed them off after considering their potential from an engineering perspective.

I am a structural engineer; as such I occasionally design building frames with dampening systems incorporated, when in a seismic region. The principles of dampening on a bike really aren't much different than dampening against seismic motion in a building. Anyway, as I see it, here is the gist of it:

Dampers work substantially to gradually absorb vibrational energy when the input energy is unsustained. Consider a shock briefly applied to a bike frame; a very resilient and stiff material like aluminum can allow the frame to continue its vibration for an extended period of time after the shock (riding over a bump) ends. When a dampener is introduced in the system, that device will gradually absorb the energy and cause the vibration to more quickly diminish. A good example would be to contrast how long a tuning fork can sustain its free vibration between the case of unbraced and braced ends (ie: touching the vibrating middle with your finger, which acts as the dampener - this is akin to the zerts inserts).

However, dampeners don't do much if the input energy is continuous. Well, such is the case of rough road surfaces and repeating road ripples. Frankly, I am not too concerned as a cyclist with infrequent unsustained shocks, such as from dips in the road - I just lift my seat and ride through or around them.

In short, I think the zertz inserts are a marketing ploy. Specialized has exploited a scientific principle that probably has little impact on the performance of the frame. In fact, their inclusion might do more harm by introducing a weak point in the strength of the frame, etc.

You are correct the Zerts inserts are bunk. You want a better ride buy better tires. If you care to you can ask me for a recommendation.

[Six jours]

Good to see another structural engineer (I was previously). Australian and British terminology tends to be that dampening involves water, damping involves vibration. Do the Americans not use damping?
Our dictionaries allow "dampening", but having grown up in an engineering family I still cringe when I see it used that way. This thread is the first time I've seen an engineer from any country use it. (And I cringed.:p)

[DasProfezzional]

That's very interesting Skeleton. I've always thought that (along with most of Specialized's voodoo cures,) the Zertz inserts were crap, but, well, an arts major doesn't really have much authority on the subject.

My only structural knowledge comes from bridges and bikes, and I'll second your opinion that the presence of the inserts in the frame is, from a structural longevity standpoint, a bit dubious-seeming.

[why2not]

However, dampeners don't do much if the input energy is continuous.

Huh. So you mean that all of those rubber vibration isolators that they use under deisel engines & motors & other various bits of vibrating machinery to prevent the vibrations from traveling to someplace they would be a nuscience, are just marketing ploys? I'm sure many companies can save big $ if they knew this.

[The Smokester]

If the Zerts were damping a lot of energy, that would be the same as saying they were absorbing significant energy (since it's gotta go somewhere). Thus, on a long, rough ride you would think that they would get warm or even hot (like elastic when you continually overstretch it into the plastic regime). I have not noticed these getting hot on my Specialized Roubaix.

I also think that the holes for the Zerts in the frame make the frame weaker than it would be without the Zerts so hopefully the Spec. engineers allowed for this in speccing the strength requirements (since I just bought a Roubaix :o). I haven't heard of specific problems with these production bikes although I did read that there were early problems with the prototype Roubaixs when they were first brought to their namesake Paris-Roubaix "Hell of the North" race over the cobblestones.

There certainly is a lot of hype surrounding the Zerts. I was at an LBS on Saturday and a technician there (who also owns a Roubaix) gave me a really detailed "explanation" on how these work. He said that " the vibrational waves come up through the stays and are split in two to go around the two side of the Zerts. Because the two paths are different, they reconverge at the other side of the Zerts and cancel each other out." He was very enthusiastic about this so I didn't have the heart to tell him that the wavelengths of the vibrations were many times the size of the bike and so this can't possibly be a good explanation. A standard damped-oscillator analysis would have a better chance at an estimation of their effect if one knew the appropriate parameters.

I am also interested in this question of Zerts effectiveness for the opposite reason to the OP. I would like to consider whether a metal seat post could be substituted for the carbon-Zerts post on my Roubaix without compromising the great ride. Then I could clamp a large seat bag to the metal post for ultra-long, unsupported rides. I guess the best way to find out is to substitute and try it. (OP: Wanna exchange and do the comparison?)

However, I will certainly say that the Roubaix absorbs sharp hits from the road and gives a smooth ride comparable to my Surly LHT...And that's saying something.

[CliftonGK1]

Huh. So you mean that all of those rubber vibration isolators that they use under deisel engines & motors & other various bits of vibrating machinery to prevent the vibrations from traveling to someplace they would be a nuscience, are just marketing ploys? I'm sure many companies can save big $ if they knew this.

If I'm seeing it correctly, the Zertz insert is an elastomer damper inside the frame/fork/post/bars or whatever other part they've put them inside. Any vibration damping effects will be through very slight transferrence from the stiff frame material these elastomers are butted against, however the majority of the vibration will still be transmitted directly through the frame/fork material.

A motor mount is a totally different concept. It's actually separating the machine from the surface/frame and significantly reducing the vibration that can be transferred to that surface. If the Zertz elastomer material was used as an isolation mount rather than an insert, you'd see the same damping effect (like a shock absorber.) You'd also see significant power loss due to frame flex at these damping points.

[Suburban Rider]

My Specialized has Zert inserts in the seat post, forks and seat stays. I can not testify as a structural engineer, but I know my shoulder notices the differnt. As one who severely damaged his shoulder, I found that riding my Specialized with Zert inserts in the front fork has left my right shoulder less fatigued over the course of 100 miles+ than it was on my Trek.