Truth or hype: Zertz inserts?
 

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!

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.

[OT] 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? [/OT]

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.

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)

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.

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 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.

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.

Zert believer
 

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.

Bump.

Current thinking on Specialized Zerts?

I don't know whether mechanically, they make a big difference.

What I do know is: The only objective test I've seen so far is a Velonews test on endurance bikes. They claim the older Roubaix SL3 frame is cushier than the SL4 (by design), and that both the Trek Domane and Volagi Liscio provided more comfort. Specialized is now pushing the Roubaix in a racier direction, hence the change. And that's with the weird new seatpost, which has a bit of spring action.

I've only done test rides, and so far I'm still a bit skeptical. So I may be wrong, but I believe that maybe 25% of the comfort benefits compared to a standard road bike is wider tires at slightly lower PSI; 25% is geometry / longer wheelbase; 25% is frame material; 25% is rider expectations. ;)

The new Specialized CG-R (Coble Gobl-R) seatpost has nothing but very positive reviews. Expensive though and doesn't do anything to help with hand buzz. Carbon fork fixes that, though.

Right now demand is outstripping production, but they should have that fixed in a month or two.

I replaced the Zertz seatpost on my Roubaix with a cheap Felt CF seatpost, the ride didn't suffer...if anything it improved - but I did a saddle swap at the same time, so could well be the new saddle (Fizik Antares Wing Flex 00, the Specialized sp couldn't handle the braided carbon rails ). I saw some test somewhere where the Zertz seatpost came in behind the set-back Thomson for comfort, go figure.

Thanks guys. I'm all about the comfort; I like to do fairly big rides (53m today) and I'm not racing, so might as well enjoy the ride!

IMO tires are the overwhelming factor in comfort. The difference between a 23mm tire and a 25mm tire would totally mask any possible contribution from Zertz.

Maybe it's just me, but I actually haven't noticed a big difference in comfort based on tire width. To me, 100psi feels like 100psi.

Sure, but if your weight and road conditions require that you keep a 23mm wide tire inflated to 100psi to avoid pinch flats then you should be able to reduce the pressure to about 85psi with a 25mm tire. That'll still be enough to avoid pinching and should give you a more comfortable ride.

I agree with Clifton - if the frame had a piece of vibration-damping material inserted in the frame in such a way that vibrations would have to go through it I could see a significant comfort benefit, but the Zertz inserts are placed so the vibrations can just pass around them and therefore any damping will be negligible.

Would that be a laden or unladen LHT ?

If I could put 100 PSI in my beloved 42mm Hetres without them exploding, I imagine the ride would be jarring. But I wouldn't do that - and 42mm Hetres make Zertz seem like a pretty dumb idea.

Of course, when I'm trying to go fast, Hetres aren't my first choice. If I'm stuck with clinchers, I'll go with something like Challenge Paris-Roubaix. Thankfully, I'm not stuck with clinchers, so my "fast" bikes wear 27mm Dugast or FMB tubulars - which, again, will make a fellow wonder why Zertz even exist.

I wrote this for my blog when my wife got her Ruby:

Zertz, of course, is the new miracle elasto polymer made with meteorite dust and the molecular essence of hybrid rubber plants grown in secret silos miles beneath the surface of the Earth.

While Zertz has shown potential for curing both Attention Deficit Disorder and warts, it also has applications in underwater welding and bowling ball construction. But where it really shines is in vibration absorption on really pretty bicycles (RPB.) It apparently can work it's magic on any bike, but does best on women specific red and white varieties.

Naturally, being of such high scientific and artistic sensitivity, this appealed to Tricia. Or maybe it was that she had a Ruby Red Giro Helmet and matching Sidi shoes already. It gets a bit fuzzy here for me. Anyway, she saved up her allowance from the local middle school, did some extra chores there, and the next thing I knew I was standing there saying stuff like "Of course you should buy yourself a new bike. With Zertz. It's not just on the frame you know, it's in the seat post too. You'd be crazy, double crazy, to not get it." and "White bar tape! White seat! What could be more practical than that!"

She often listens to my experienced wisdom when it comes to important matters like this, and she did this time too.

So, here we are, announcing the latest addition to the Tricia stable: Ruby.

Photos here: http://ccorlew.blogspot.com/2009/06/zertz.html

From what I've heard, it's more the frame shape and composition around the Zertz and the fact that there is a hole through the tube that gives it the extra compliance. Whether that hole is filled with air or Zertz doesn't make as big of a difference as the fact that the hole is there.

Like the Trek Domane?

The Zerts seemed like a marketing ploy. Always interested in supple tires. Have settled on Continental 4000 Gran Prix 25c. What else is out there to try? Just noticed the date of quoted post!!

Not a structural engineer, but ... I've always seen those diesel engine and equipment mounts called, engine mounts or equipment mounts, or isolators. Lord is a well-known supplier. What's in common is that extra or undesired kinetic energy is converted to heat in an elastomer or (in old cars and motorcycles, probably pre-WW2 era) friction among a group of disks.

In electrical engineering, which is my area, we have problems that are mathematically similar to the damping problems the structures guys have just discussed, and we call it damping, not dampening. As a verb, it would be "to damp," rather than "to dampen."

Was kind of interesting to read the "arguments of opinion" from those who discounted it but never ridden one. I agreed and likely done the same myself but I would (based on a survey of one) been incorrect.

My friend, doctor and cycling buddy owns 11 bikes and has purchased half again that many that he has sold. He has only ridden road bikes for exercise and cycles about 4-5K miles each year. He bought a specialized bike with the Zertz inserts. We have tar and chip roads around here for much of our routes. They're generally pretty smooth but there's that constant rumble of road feedback. He says the difference is "amazing". On top of that, he's ridden solo TT's on one of our courses (19.6 miles) and broke his 10 year old record by roughly 1 minute. The bike has nothing special over his older ones (wheels basically same profile etc) EXCEPT energy losses to vertical displacement of unsprung mass. That is, of course, my opinion only but I'm a national TT medalist and cannot for the life of me see anything special about that bike except those inserts. They wouldn't help a bit if the course were silky smooth but it reminds me of my change from an aluminum to carbon fork. My smooth courses were the same speed but my rough courses got substantially faster (about 1 mph sustained over the rough surface).

Do have any idea about quality of Zerts ? is there any deformation, that depends on usage ?

regards

This is a really old thread, are there still bikes made with these inserts? It seems to me that the problem they were meant to solve, road vibration, has been solved by most carbon builders in other ways.

Another structural engineer chiming in and I just wanted to add that there is a "cancelling" effect at the split, and that is what does the job. It is not as significant as adding a shock (due to several factors, isolation being one, as in a motor mount) but there is a ride improvement via a simple concept.

At the end of the day (or ride), if it works for you then it is worth it. The Roubaix is a great bike and rides smooth, but so do other bikes without the Zertz.

BTW, I own a Roubaix, lol

I took an older roubaix out for a spin yesterday and it wasn't much different from my vintage steel roadie as far as road buzz, the roubaix had harsh 23mm tires though and I had supple 25mm open corsas on the road bike and the ride was pretty similar.