William Powers, a team member of a new start-up group called PumpTire LLC, informed me a few days ago of their self inflating tire idea. James of Bicycle Design had posted on his blog that he received the same email as well so I figure that this made the rounds to many bloggers in a mass email.
The idea appears to be the brainchild of Benjamin Krempel. The internet describes him as a CEO of Aqueduct Medical, a company that develops "safe, effective, user-friendly products that improve patient recovery from facial and cosmetic surgical procedures."
In the video below, he describes the idea (although somewhat vaguely) :
So its basically a pump that operates every time its squished by rolling motion. "The tire is a 26” x 1.5” tire with a set pressure valve", says the product website. Reportedly, the tire inflates from zero guage pressure. "The pumping mechanism will pump from a flat up to 65psi."
In a blog entry back in 2008, I listed some "new" cycling ideas that would be serve as cool thought experiments, without exploring any technical or economic aspects. An "on the go tire inflation/deflation system" was first on my list and it had an almost science fiction aspect to it - the idea that the tire would have a feedback system to it to monitor pressure while riding and adjust itself after sampling pressure.
One application where this would be attractive is in public bicycles used for bike share programs where a self inflating mechanism could possibly add to some convenience. It avoids the necessity of adding an extra infrastructure for pumping air by the sidewalk or the need for individuals to carry pumps. For utility cyclists, terms like "rolling resistance" or "wheel inertia" are usually unimportant. Most just want to get from point A to B.
Having said that, a safety feature in the system is a must. The tire shouldn't injest water along with air. It also shouldn't over-pressurize and lead to tire bursts. Things like that. In the end, an interesting thought experiment ends up consuming time being developed, tested, re-tested, re-designed, at the same time needing to raise funds for the development and meeting the demands of consumer standards and regulations. By the end of it all, the inventor will want to go for a serious ride to breathe some air.
The idea of a self-inflating tire doesn't appear to have sprung up now. A few others tried to do something on similar lines, one of them if I remember correctly was an entry for the Specialized : Innovate-or-die" contest that happened a few years ago.
Here's Sean Conley back in 2007 :
And here's Kevin Manning, also in 2007 :
Both appear to charge air into the tire through pedaling. A bunch of patents on "self-inflating" tires for cars and bicycles date back to 1800's. Those can be found by a Google Patent search. That's what happens when you give people too much leisure time.
Whether Krempel actually first came up with the idea or not is not the issue. The big picture as I see is perhaps that of the slow march of the bicycle towards fulfilling an intelligent, self correcting system. Automobiles, ships and airplanes are already there but the "control architectures" in these complex systems are the by-product of externally driven factors - federal laws or economic incentives. Will the bicycle really benefit from that kind of intelligence? Sounds like a philosophical question.
Do bicycle chains get stretch marks? Will smearing cocoa butter on them be a step in preventive maintenance for future? I don't know, but hold that thought for a moment.
I, like many, am a fan of chains. For bikes, they present a technology that is ubiquitous, economical, and proven to work almost seamlessly with external shifting systems. Belts are slowly staking their claim in the single speed road and mountain bike arena, however I have to be honest - show me a more simpler, self cleaning power transmission mechanism that doesn't load up shafts and bearings as much as a belt does, and I'll be sold on other ideas.
".. the less stretch, the more responsive the bike becomes.."
But in cycling, as we all know, equilibrium is rare. Everything has to get scrutinized more thoroughly than a coroner would do a murder victim, from the pimple on our skin that's disturbing laminar air flow to the secret ingredients used to make those mundane Presta valves and you know, that's what keeps our world a bit interesting (or not).
Now if you just may recall, Wipperman was getting fancy in the recent past by testing a host of chains in order to rate them according to their wear rates. You can read that blog post here which described the test protocol, the results they came out with and so on.
Recently, I was told that the company commissioned a different test on a similar selection of chains to test for elongation under load. Tom Petrie of Cantitoe Road - a chain test data center - passed along some literature that said the following :
"Wippermann recently tested a number of popular 10-speed chains for stretch under load. For a reference point, each chain’s length was measured under a nominal load of 10 kg. Then each chain was measured under 75kg and 150 kgloads, and the results recorded. Not surprisingly, chains with cut-out plates and hollow pins stretched more than those with solid plates and pins. And, the chains that stretched least were the Wippermann’s Connex 10 series with solid plates and pins!
How much a chain stretches under load affects how quickly the load is transferred to the driven cog. The less stretch, the more responsive the bike becomes. And, less stretch means less energy is lost to stretching the chain! Especially in sprint, time trial, or hill climb events, reducing these losses is critical.
Wippermann tested 31-link sections of chain. This is the average number of links under load between chain ring and cog. While the actual amount of stretch is small (from 1.10 to 2.15 mm) the differences are substantial. Among the various chains tested, the “stretchiest” stretched almost 100% more than Wippermann Connex!"
After testing, the data was cobbled up into a table to make sense of the results. They follow :
Summary of chain stretch test data
Elongation vs load plot
The document went on to make light of these :
"In addition to raw material and proprietary heat-treating processes, the shape of Wippermann Connex outer plate is largely responsible for its resistance to stretch. Note that chains featuring elaborate side-plate cut-outs and hollow pins are the “stretchiest” while chains with solid plates and solid pins stretch less. But even solid-plate solid-pin chainswith sculpted “figure 8” outer plates stretch more than Wippermann Connex. The extra-strong rectangular outer plates on Connex chains contribute significantly to their resistance to stretch."
This stretching they're talking about should be nowhere big enough to cause a yielding in the chain material. So the material attains its original shape after unloading like a spring, and the real question then becomes - how will a 100 thou inch change in chain length in the worst case scenario affects overall power transmission efficiency? Is it any more significant than the normal vibrations introduced into the chain due to tensile load changes and sprocket tooth effect? Does the stretching get better or worsen in weaker chains when the chain is misaligned/cross chained? Finally in the big scheme of things, how will cyclic stretching/unstretching react with notorious elements like salt water? Could it possibly accelerate the failure of cut-out chains in those circumstances?
What do you think? While you sip your coffee, you may also be interested in glancing at a"shifting performance" study done on chains through Wippermann, the hardly surprising conclusion of which was that there is no observable correlation between a worn chain and shifting performance compared to a new one. You just may not want to break your bank over a chain.
If you're the type who likes to gun it down the line in high gears, you may have wondered more than once - what is really better in terms of crankset chainring-rear sprocket size, would it be a 52T x 11T or a 52T x 12T?
At the same RPM, you get a slightly higher top end speed with the 11T at the sacrifice of some torque. But if you're asking this from an efficiency standpoint (ratio of input power over output power), its a slightly tougher nut to crack if you don't have actual measuring equipment.
I won't talk directly about efficiency but I'll talk about something else that you may want to start connecting, perhaps more with equipment durability than efficiency.
A bicycle chain has links, connected by a distance called pitch which is usually 1/2 inch in bicycles. When you're riding your bike at a cadence of 100 RPM, the chain has an average velocity called pitchline velocity. At the sprocket though, some interesting things happen with chain velocity.
For one link in your chain to engage a teeth in your sprocket, the link has to swing about an angle before the roller is seated between tooth. This is called Angle of Articulation, calculated by using the relation : 180/T, where T is the tooth count of the sprocket.
For a 11 tooth sprocket, the angle of articulation is 16.36 degrees, while for a 12 tooth sprocket, it is 15 degrees, a reduction of 8.3%.
Because the chain is turning at these sharp angles at the same time impacting the teeth, the velocity of the chain is not constant, but infact fluctuates between the maximum and a minimum each cycle. The maximum occurs before engagement, the minimum occurs after the link has swung in engagement. This change in velocity is called Chordal Action.
The point is that chordal action results in fluctuations in chain transmission and may be minimized by reducing the angle of articulation, which decreases with increasing sprocket size. For 11T and 12T sprockets, which are about the smallest standard sizes you can find in the bicycles, the angles are tight which results in uneven exit velocities.
But is it something you should worry about? The math is complicated to present here so I just did all the calculations myself elsewhere to look at chordal action. Perhaps you can decide whether it matters or not after looking at the following theoretical numbers.
Say you're riding hard at a cadence of 100 RPM with a 52 front chainring. The RPM at the rear sprocket is multiplied by the gear ratio, which results in 433 RPM with 12 T and 482 RPM 473 RPM with 11 T. With a 12T sprocket, one cycle of tooth engagement sees a 3.4% variation of chain linear speed, whereas an 11T sprocket sees 4.1% change in linear speed for the same because of the tighter angle the link has to swing.
Here are two graphs I generated :
Note : Chain velocity is a function of pitch circle diameter, RPM and articulation angle
What this does for transmission efficiency in bicycling is moot. What I wanted to present before you is the fact that chordal action is real in small sprocket sizes, and it has an effect on your tooth wear and pulsating motions at high RPMs. But it may not matter in low cadence (60 and below) and if you're using wear resistant, hardened sprockets. Feel free to discuss.
Now if you don't use the Campy recommended, "200 dollar" chain tool to hook up your 11 speed chain, it will break. If not now, at some point. Because of the smaller tolerances and a special peening procedure involved, your conventional tool will not be able to seat the union bushing into the links properly. It will bend out and take the paper thin link along with it.
Only the mighty Campy tool can properly do the following while crapping in your wallet :
a) Supportthe left end of the link by clamping it while pushing the union bushing in adequately with a conical pusher.
b) Splitthe protruding end by a special holeprovided in the tool.
c) Lock the bushing in the link ("locking the link").
Trust me, this is the Cadillac of chain tools. Your grandpa's tool just won't cut it.
Now I myself thought I could somehow get away without 'following the rules'. Oh no. Didn't work.
The following chain failure happened to me while climbing a long hill. I asked my local bike shop to equip themselves with the right tool and had them fix me a new chain. (I think its the right thing to do for them as now, it is likely that customers increasingly show up at their place with a 11 speed job)
Hey, just check out the width of this chain. This is technology right here.
Now start being amazed and see how a 11 speed chain is installed :
Recently, my 5 year old Park Tool floor pump started bleeding from its ears. The gauge hose ruptured and there was a major air leak, rendering the pump useless unless I replaced that hose (this is one of the most common failures that could happen to any pump, so if you don't want to be irritated, consider keeping a replacement hose with you for safe measure).
Since the pump was old anyway, I decided to get a new one instead.
Anyway, just for fun, I opened up the pressure gauge of the old one to show you what is contained inside of it. I'm sure some of you may have wondered...'hmm, how on earth does my pump detect the pressure inside my tube?'
So what is the pressure gauge anyway? It is a pressure sensor, right? And what does it do? It does the following 3 things :
1) It senses the pressure to be measured. 2) Part of the instrument responds physically to that pressure by stretching, bending or changing positions. 3) The instrument then converts this response to a pressure signal which, in our case, is in the form of the needle moving along the dials of the scale.
Park Tool's pressure gauge here is a dry instrument (no liquids), and looks to be a C-shaped Bourdon tube, named after Eugene Bourdon, a French scientist who invented it in the 1840's. This is basically a bent tube in the form of a C that actually straightens out as the pressure in it rises. So consider that it acts like a spring that stretches when pressure is applied.
One end of the tube is sealed shut, while the other is open to process pressure. This straightening out is converted to a signal the human can read through a geared linkage connected to the pointer or needle and a pressure scale. As the tip of the tube moves, it rotates a sector which turns a pinion attached to the dial pointer.
See the diagram below and you'll go : "Wow, that is clever!"
Now say that you use a pump for over 5 years. Think about the number of times this tube stretches and unstretches. Isn't it amazing that this elastic material can undergo so many cycles of flexing without fatigue or hysteresis? I'm not sure of what this metal is, but it maybe a phosphor bronze, or a beryllium copper. Maybe even monel?
More later. Take care now.
P.S : Say hi to my buddy's new puppy. Her name is Olive. Hey Olive, you're on the web!!!
Update : Before you read the following article, it may perhaps do you good knowledge wise to read a small analysis of the bicycle "endo", that I wrote recently on this blog. While it is physics driven, it will give you an appreciation for what happens when you apply brakes suddenly.
* * *
Front wheel lockup upon brake lever activation is something that often sends riders (beginners and experienced alike) to pitch-over the handlebars and get injured often seriously. We are all told to feather the front brakes, and apply more braking to the rear wheel especially in a downhill scenario. But what happens in a panic situation? We are all bound to get the shivers and haphazardly slam both levers with full might in the hope that it will stop us quicker. But that's when the front wheel locks up, the bike skids and off you go toppling over the bars.
Now, can a mechanical contraption be made to commit to such braking control automatically for you while you enjoy your ride?
Thats where this nifty little device comes in. I contacted Bud Nilsson from Lodi, CA to explain his patented invention to me and perhaps send me his last sample (incidentally, he had it installed on his bike) so I could take a look at it and see what it was for myself. I have previously introduced the brakes to readers. See here. I always welcome ideas to make cycling a safer experience.
The Budbrake is about the size of your cell phone and is installed close to the levers at the front. Brake cables are routed to this mystery black box before they are connected to both brakes. There is a level of much abstraction to it, so much so that it compels curiosity. With this installed, one immediately observes that no matter which brake lever is pressed (either one or both), the system ensures a safe stop by activating the rear brake slightly before the front.
Magic?
Budbrake : A brake modulator in a mystery black box
'Mystery black box' didn't come as an understatement. I didn't understand how it worked before I got the sample. The mechanic at The Bike Shop in East Aurora close to where I live had in fact no clue why it worked the way it did. And many others likewise, are confused, says Bud. He told me : "There have been many engineers, technicians and product managers testing my brakes and all are impressed with the performance and agrees that it does work but wonders how does it work and 'why'!"
Here's a small video I made. We had the device installed on my friend Dave's mountain bike.
SO HOW DOES IT WORK ANYWAY?
Instead of muddling readers with my own logic, I'll let Bud himself explain what his design philosophy behind this clever little device is. Why do the rear brakes activate first? What prompts it to do so? What on earth is in this black box?
"Ron. I will explain my reasons for this design. You are an engineer and I hope you will understand my theory. I will also welcome any comments on it.
See, the bicycle frames of today are designed in a way that places more of the rider's weight over the rear wheel for better traction when transferring the power for forward momentum. The saddle is behind the center point between the wheels and the bottom crank is forward of the seat post. You get more power when pushing the pedals around this way and you transfer more weight to the rear wheel. Consequently the rear wheel has more traction than the front.
In the first moments of decelerating speed control (applying brakes), the Budbrake automatically applies the rear brake first when it has most traction for braking. Due to the dynamic forces and forward momentum, the front wheel gets more traction and at that time, much of the momentum has decreased anyway due to the rear brake initiating the speed control.
Therefore, I designed the modulator as a mechanical means of proportional distribution of power to the brakes, just like the proportional valve (hydraulic) in the automotive braking systems to prevent front wheel skidding and maintain traction while turning.
Now do not confuse this with Antilock Brake Systems (in automobiles, there is only one brake pedal for front and rear brakes). The main objective of the Budbrake Modulator is to automatically brake the rear wheel since it has more traction, slightly before the front wheel and with more brake action compared to front, therefore eliminating unwanted skids and mishaps.
There have been a lot of bicycle engineers and technicians that can see that it works but do not understand why and how. The Modulator controls the brakes by changing the cable tensions via alternating the length of the casings, front and rear, not the length of the cable. Again, regardless of which brake handle is activated - front, rear or both simultaneously - the rear brake will apply first and then the front and automatically feather or modulate for balanced speed control. I guess the main difference from conventional braking is that the Budbrake alternate the length of the casings to achieve the goal.
If you take a look and think about the offset fulcrum point inside the Budbrake, that is what makes the rear brake apply first. When the rear brakes make contact, the system then applies the front brake. The offset pivot point, (fulcrum) and varying the length of the casings produces the automatic modulation action. This is the trick for safer speed control .
The Budbrake has been field tested and lab tested for 650.000 braking actions. It was also tested against the CPSC criteria for bicycle brakes and it resulted in superior performance against their criteria.
The product managers at Giant looked at this and told me that if one cable broke, the brakes would completely fail. I did not want to cut or brake the cables so I disconnected one at the time and tested. The stopping distance decreased (as it would without the Budbrake) but the brake, front and/or rear worked. It is a fail safe product as any other. Now if both cables snapped, then the system is trash of course.
I also took one unit and drove over it with my motor home front wheel. The unit broke somewhat but actually it still would work. The black plastic material I use in the injection molding is not ABS like most people are used to. I am using the toughest composition that I can find available and it has a Teflon in it for lubrication of the pivot. If I used ABS in production the price would be at least less than half, but I want to produce the "very best" product for cyclist's safety.
I am thinking that the reason I have a hard time to get the Budbrake accepted and on the market is that the bicycle engineers , product managers and marketing people do not understand " why" it works. I'm not much of a writer but I hope I explained this to you and your readers in a simple form. "
A big question in Bud's mind is how he can get his invention accepted. Having seen and tested it, I think it has potential for beginner riders and anyone who wants that extra margin of safety. So this is to you readers : Would you rather bike with the Budbrake or without it? What are your thoughts and feelings? Think about it and let us know by dropping your comments.
* * *
An example of a crash caused by excessive front wheel braking and moment about the same caused by high forward center of gravity. Notice that a rider's vertical fall drop is much more on downhill that if it were a flat section. Possible injury could be a wrist or collarbone fracture, or the possibility of planting your entire face into the rocks and dirt.
I wrote earlier about two recent incidents of Thomson Elite seatposts breaking during use, without any prior warning to the users (see here and here). I persisted in trying to extract as much information from Thomson about these happenings. Two phonecalls and an email to them never went through due to some obvious hindrances but just earlier this week, I was able to converse with David Parett, a manager and PR specialist at L.H Thomson Inc. Although they are a relatively small company, they seem to take pride in the fact that apart from the cycling side of the business, they're also a contract manufacturer designing and making parts for clients such as Boeing, Trane, Ford, Coors, Reliance Electric and so on. One can imagine that to gain the trust and business of such big name companies, you'd find it absolutely necessary to have sound manufacturing and quality control down on the floor.
One of the owners of the posts (with the broken head) sent it in to Thomson for analysis. When I talked to the user, he made the comment that he was 100% certain he used a torque wrench to tighten the bolts before use (documented here by 'Apacherider'. He reported he used a Park Tool torque wrench that only goes to 60 in-lbs which is the max torque recommended by Thomson for the bolts). However, the following is what Dave had to tell me from first impressions. Read it, and leave a comment if you would like to roundtable a discussion.
Dave : "There is no question that this failure was related to torque. This was easy to see as when I got the broken post, two divots caused by the bottom clamp had formed in the cradle of the post. We know how much torque that takes, and it is a big number. The user may feel they torqued it properly but there is ample evidence that is not true. I think most parts will fail if abused in such a manner. Imagine overtorqued handlebars, stripped pedal cleat bolts, etc. Or think of a car. If you torqued a sparkplug to 3 times the suggested value,what do you think would happen? We know from testing here at Thomson that there is no other way one could create those divots unless you overtightened the clamping bolts."
DISTORTED BOLT HEADS
Dave : "I also observed that the bolt heads are distorted. The bolts are grade 12.8. We know how much torque it requires to distort the bolt heads, and it is in excess of 125 inch pounds. Further, the metal shows no signs of material contamination, and the post is within spec as far as dimensions go. We have a lab here and we have examined the post. Moral of the story is, 2.5 to 3 times the recommended torque will break things."
ANODIZATION AND FATIGUE LIFE OF 7075-T6 AL
Dave : "I verified our anodic coating thickness. It is about .001" thick. Yes, anodizing cuts fatigue life, almost to 50% the original. But we engineer around that. Our post is heavier than it would otherwise have to be to deal with that. If you thinned it out, it would be susceptible to being crushed by clamping. Paint or powder coat cannot provide this kind of corrosion protection.The ridges may help with slipping, help keeps the finish from scratching and is also cosmetically appealing to some people. The finish changes near the radius at the seatpost head to help prevent stress riders."
Dave : "The other post has not come back here as far as I know, but all our testing indicates it takes in excess of 600 pounds of force to cause an ear to fail and it would not fail in the manner it did. A brittle failure like that is again related to torque. Testing here shows that the original design idea is still valid. A riding event or accident results in a bend. All components of the top of the post, bolts, clamps, barrel nuts, ears are stronger in relation to the tube. If there is a big hit, the post will bend and the clamping mechanism will not fail. You can negate this by putting the ears under severe tension with torque."
SOURCING, STANDARDS AND QUALITY CONTROL
Dave : "The anodizing is done in Reading, PA, The Al ore is from Quebec, CA and the extrusion is done in Minnesota. All the fasteners are from Chicago and Cleveland. All of them are certified and rechecked by us. There are barrel nuts and bolts in receiving inspection right now, placed under a heavy load. If we observe any failures in the entire shipment, it will be tested and possibly rejected. I don't think anyone does that but us.
From filming riding, we have a series of in-house tests that were used in design and are still used on every lot of material. Bolts, washers and everything are checked for ultimate strength, fatigue life and corrosion resistance using a 500 hour salt spray test. We also had a German lab check our posts to the CEN standard. We think the CEN is a poorly designed test, but we passed it as well. The 500 hour salt spray test is run on samples from each anodize lot to verify quality. Further, we have a fatigue tester. We can put a post in it, set the bolts at the level the customer had them and create that failure. There just is no question of what happened after that.
We expect our products to last for 10 years in the field under normal conditions. If a customer experiences an issue, we replace the part for goodwill. My frustration with all this is there is not a single company out there that does 10% of what we do to check incoming material quality, 100% checks at each machining operation, and certification and testing of all components. Our bike parts are built to the same standards, in some cases higher, than the airplane parts we make."
31.6mm OD, 410mm total length with 5/8 inch or 16mm of setback.
Used on a Cannondale 29'er (offroad XC bike).
Made in USA with 7075-T6 Al alloy and anodized black to a glazing finish.
Post is machined and the head and post body are integral units.
User owned the product for 10 months.
Approx 2000 miles of use, mostly on pavement, some on fireroad and some singletrack.
Never been dropped, wrecked, knock over or even clamped in a repair stand.
Cannondale saddlebag was velcro strapped around the rails and post with nothing sharp in it contacting the post.
Owner weight = 190-200lbs. No indication of a weight limit in the instruction sheet.
Owner followed Thomson instruction sheet for installation and use "to the letter".
Saddle was installed far back on the rails beyond neutral position and the result was that the post was clamped on the forward 1/3 of the usable rail portion.
Owner was immediately replaced with a new post by Thomson over the Easter weekend.
Macroscopic features of the fatigue and final static rupture are easy to observe in the broken sample. The fatigue crack originated on the front side of the post body, propagated with loading cycles thus smoothing out the surface as it progressed. The static failure happened at the back end of the post, and these areas have a rougher appearance.
In this picture that shows the underside of the head, it appears that there was one 'dominant' fatigue crack on the tension side of the post that initiated this process. Observe the darker 'slit' near the arrow.
What's bothering me at this point are the following :
1) Thomson's marketing materials online claim that at around 250 in-lbs of torque on the post, the product will start yield phase and bend at the seat tube clamp. There is no evidence of any bending, either on the rails, or on the clamping site, from the original photos.
2) An elliptical bore leaves more material on the front and back ends of the post, in order to withstand bending stresses. Material is removed from the inner sides of the bore to reportedly, save 30-40 grams of weight. This structural design did not prevent this failure.
3) Does anodization reduce the fatigue life of this seatpost? In other words, did Thomson test the seatpost in post-anodized state? Anodizing significantly reduces the fatigue strength of Al alloys. As Al bends elastically, the anodized surface cracks and the crack grows into the body of the Al. Anodized aluminum only worsens the fatigue limitations of Al. You can't bend anodized Al significantly without cracking it. The cracks that develop on the coating are stress risers and potential sources for fatigue failure in the substrate metal.
4) Additionally, if one closely inspects the outer surface of the seatpost, there are grooves all along the length of the post. This may not be seen at first glance but can be felt with the hand. I'm not sure what functional purpose this serves, other than aesthetics. Is this done to reduce seat post slippage while clamped and loaded? Whether these features have any role to play in the breakage is something to be further studied.
If you use an Elite or a Masterpiece seatpost, it won't hurt to periodically inspect what's going on with the post. This type of failure is very dangerous largely because it is hidden and away from the sight of the user, happening well below and under the saddle. I hope Thomson takes this seriously and undertakes a root cause analysis before any one gets hurt. While replacing the product for free addresses people's concerns to some extent, it still doesn't take care of the problem.
Readers will remember that a couple of days back, I ran a controversial story of a Thomson Elite seatpost that broke off at one of the bolting ears due to a "fall". I placed known marketing information about the product alongside the given failure situation. Why some readers were irked is hardly surprising, since the Elite is widely considered as one of the best designs in the market. For many, it has provided years of faithful service.
Did you know that the Elite seatpost has an elliptical bore?
So what has made this seat post so popular? It must be in the design, right? Please see the latest update to my previous post. I go through most of the design features of the seat post and comment on its attributes with the help of high resolution photos. I also run through the product manual and high light some of the factual installation warnings that Thomson has made clear pretty upfront. A seat post failure while riding can be absolutely dangerous, no question about that. Hence, installation directions and warnings cannot be taken for granted and ignored however mundane reading them maybe.
"The real question is, 'Does the design work really work?'. The short answer, “OH YA!” The wide stance and vise like look of the eebrake translates directly into outstanding braking performance. Optimized leverage and modulation is realized through our multiple lever system. Our efficient structure does this all with a minimum weight; less than 200 grams per complete brake set with pads."
With the economy in shambles, and people trying to be more conservative with their money, here's a party launching out another 500 dollar brake set to market. Whats wrong with cycling?
The new 5 pivot EE brake is sure to polarize. They are ornately crafted, and on the surface, there seems be be some real work that has been put into them. In this age of KISS (keep it simple, stupid), you may have to like steam locomotives or complicated medieval torture devices to comfortably find pleasure in this creature.
However, for their steep asking price, their website was choke full of marketing hoopla and devoid of useful information. A cautious/intelligent consumer wanting to know how on earth their 'multiple lever system' generates better modulation than what was previously realized is left with little but a colorful picture of an FEA screenshot that's too small and blurry to even understand.
That is a little substandard.
If you want someone to part with their precious coin in your favor, your first rule of thumb is to give them a good reason 'why'!! Words like "bigger", "super stiff", "beefy", "pure awesomeness" etc are a tad bit overdone these days to lure someone to purchase.
So in my honest opinion, you're missing the beat. Since your design is unique, it opens itself to serious scrutiny. I suggest you consider writing a white paper on the brakes and posting it on your website so as to back up bold claims. How do your brakes work and how is modulation enhanced compared to the best dual pivot offerings? I certainly cannot see how. Give us a free body diagram of multiple leverage action. Is the mechanical advantage constant? Is the brake behavior linear or non-linear? Explain briefly the FEA involved. Pictures don't make sense if you can't read them! And if you have testing done, show us some numbers from the setup runs. This is good, and proper engineering practice.
This way, we'll hope to arrive at a conclusion as to what those extra dollars/gram is doing. Are they :
A) Affording one comfort and peace of mind in installation/adjustments and superior performance exactly as promised at the brake end?
OR
B) Just a feeling of psychological advantage of possessing a lightweight product, which is then quickly canceled out by application inconvenience through over-complication?
EE Brake installation must be meticulous and doubles the time required for simpler designs. This reviewer showed a picture of sand and grime in the linkages, and reported a nasty-sounding “crunch” when the brakes were used in wet weather (5 pivot means 3 additional crunches than dual pivot).
FEA snapshot. Good looking but deliverables are zero.
A clipping of the sequence of steps involved in installation. A mechanically disinclined person might need a fair amount of coffee to get through this successfully.
Despite all the reputation that Thomson has in making reliable cycling components and giving the best cushions against catastrophic failures on impact, this person's Elite seatpost (in particular, one of the bolting ears that stick out sideways ) broke off like chalk piece after a fall. The bike was leaned on a wall when it tipped over and fell sideways. Hence, the owner was apparently not even seated on the bike at the time of impact. The seatpost ear broke as he straightened the bike and it dropped in his hand. You can read some back and forth question/answers between me and the owner of the post as you scroll down. That will give some background information into the incident.
Compare this to Thomson's marketing literature online. Among several other things, the company happens to generously regard itself as producing the only seatpost in the market incorporating a "bending fuse" against catastrophic failure.
Their website says :
"The Thomson seatpost design incorporates a bending fuse to prevent catastrophic failure. All brand-x seatposts we tested - every one of them - failed in catastrophic failure with the seat and clamp components - and sometimes pieces of the tube and head - flying off in all directions. This type of failure would dump the rider."
And something about impact absorbing clamps :
"Impact absorbing clamps - clamps, head, and assembly will spread and flex on impact to protect seat, rails, seatpost and rider. Easy on seats - allows seat to survive heavy impact loads without bending rails."
The owner of the seatpost, however, had a contrasting experience. He wrote on his blog after the incident :
"Forget the hype! Despite the claim that their seatposts are over "40% stronger" on ultimate strength test than the strongest production seatposts on the market, the Thomson Elite seatpost is not tough enough to withstand even a simple fall. And here's proof of that! This four-year-old post on my GT broke in the upper tube area, which is apparently 'strong enough to withstand 350 foot-lbs of torque', when the bike took a tumble sideways while it was stationary. It didn't "bend slightly" on impact like what the Thomson folks had you believe would happen but just crumbled like a cookie at the top. Actually, the OEM seatpost that I was using before I got the Thomson in a moment of weight-weenie lunacy seemed to take much harder knocks! And it looks like it could take plenty more! So, if you've got an Elite seatpost on your bike, watch out mate! It could be a disaster waiting to happen. "
I'm not sure what went wrong at Thomson's end to cause the seatpost to be brittle, but I'm just going to have to drop this one in the "Marketing Mishaps" section for now. This doesn't mean your Elite seatpost has the same problem. But it won't hurt to be informed. Out of 1000 apples, its likely that 2 end up being bad and that's the nature of manufacturing. When those bad apples that dont meet the standards turn into the customer's hands, that's where the issue reveals its uglier side. If Thomson stands by their word, they should delve into this incident and redress the issue (i.e If they are responsible. Corrosion, or user over tightening cannot be ruled out at this stage).
Take note that the lighter weight Masterpiece seatpost is essentially a machined out Elite. Also note that I suspect some of the brittleness MAY be caused due to anodizing, since the anodized Aluminum Oxide on the surface of the substrate is pretty brittle, even though hard. When the part elastically deforms, the oxide layers starts cracking and it propagates down into the substrate metal. This will only reduce the part's fatigue strength. [Source : Aluminum And Aluminum Alloys by J.R Davis & Associates (ASM)]
* * *
UPDATE March 19 12:00 pm
A CONVERSATION WITH THE USER OF THE SEAT POST
TO THE BLOGGER OF KHABAR BIKE (and user of the seat post) :
Due to the number of requests I'm getting to dig further into this issue, I have to put you in the spot light by flexing my Bee Muscles (crunnch). Please tell us the following if you don't mind :
1) Did you over tighten the seat clamp outside limiting values specified in the product sheet?
Khabar Bike : Not as far as I'm aware of. And it's been untouched since I last changed out the saddle about a year ago.
2) Did you wash the seat post a number of times without letting drying it out? Or have you used the bike a good number of times in the rain?
Khabar Bike : Definitely not. And I hate riding in the rain.
3) Is this the first time that the seatpost fell, taking a hit on the same area on the post in question?
Khabar Bike : Yes, as far as I can remember. And this is the first time I've ever had a broken seapost in the 12 years I've been a serious bike buff, with seven bikes including a lugged steel Pinarello, an old Trek bonded/carbon road bike and a 12-year-old Gary Fisher hardtail. They have a Syncros, ITM or OEM seatpost.
4) Did you buy the post from a recognized Thomson dealer? Brick and mortar shop? Online? Ebay? The possibility of a knock-off cannot be ruled out.
Khabar Bike : Yes. My LBS is one of the most reputable in the area. And the seatpost (paid about $70 for it) came with Thomson's unique but pretty useless bag and folded manual. I also have another Thomson seatpost (with layback), on my hardtail, which has been holding up fine for more than three years.
5) Pretty Useless Bag... the manual was in this useless bag. Did you read it?
Khabar Bike : Yes, I did and didn't find it useless at all.
6) Do you recall how the bike fell (orientation)?
Khabar Bike : It fell sideways. I picked it up by handlebar and the saddle and the back part broke off in my left hand.
7) Were you riding it when this happened (added weight) or did it free fall as it tipped over (just the bike weight)?
Khabar Bike : It was leaning against the wall when it tipped over.
8) Did the seatpost also have the saddle attached during that time?
Khabar Bike : Yes, the clamp was secure and undamaged, and still attached to the saddle.
Finally, I'd just like to say that I'm not as upset about the whole thing as I would've been a few years back when I was really into lightweight products. These days, anything that doesn't cost and arm and a leg and lasts is just fine with me.
Thank you.
* * *
UPDATE March 25
DESIGN FEATURES OF THOMSON ELITE SEATPOST.
THIS IS A WELL REGARDED SEAT POST AND MANY CONSIDER IT TO BE AMONG THE BEST DESIGNS.
KNOWN FACTS ARE GIVEN IN BLUE FONT. ANY EXTERNAL REFERENCES TO LINKS ARE IN RED.
This is the patent for the Thomson seatpost in question. The patent is titled "Lightweight High Strength Bicycle Seat Post And Associated Clamp Including Seat Angle Indicating Indicia". The main idea behind the intention was to provide a lightweight, strong seat post that has a wide range of adjustment and adequate cushion against catastophic failure.
The product is made from a 7000 series (Zn added) Al alloy and marketing materials claim that it is "40% stronger in ultimate strength tests, and has twice the fatigue life of 75 of the most strongest production seat posts on the market." The post also seems to have what is an obvious anodized black finish.
According to Thomson : "The head is not pressed or bonded in. This allows for superior strength and minimum weight, allowing higher strength at low weights."
When you first feel the seatpost in your hand, you'll come across the sharp features at the sides of the head. At the edges as shown, chamfer radii appear to be very small, hardly noticeable. See picture below.
This isn't a circular cross-section, as you can see. Thomson says : "Natural ellipse bore inside tube for optimum strength to weight ratio." The thickness is higher on the front and rear end of the seat post, corresponding with the directions of the bolt locations on the head above it.
Moment of Inertia (or Second Moment of Area) of a hollow elliptical section beam about a horizontal axis passing through the center of gravity. Practically, it is the measure of the capacity of a cross-section to resist bending. See The Design Of Structures By Samuel Anglin, C.E
The same for a circular hollow cross section
If you look carefully to the tube body section under the light close to the logo, you'll see some fine marks/grooves that extends throughout the length of the tube. Is this a deliberate feature to prevent slippage of the post when clamped at the seat tube? Its pretty nice.
Here's the top and bottom clamp together with the swivel nuts inside. This arrangement on the tube supposedly allows the claim : "Infinite tilt adjustment minus 5° and plus 29°."
The product sheet says : "All Thomson seatposts are designed with positive metal to metal stops. These positive stops and bolt lengths are designed to work together to allow a maximum 5 upto 29 degree down tilt. This means the tilt adjustment of the clamps will be stopped by the positive stop before the back bolt runs out of the nut. This prevents damage to bolts, nuts, ears, and clamps that may otherwise occur with over adjustment."
On the product sheet, Thomson mentions very clearly : "Never tighten the front bolt hard against the positive stop. Make sure that bolts are tightened against each other. Always tighten the back bolt to 60 inch lbs of torque. If the front bolt is tightened hard against the front ear, the force created by that tightening will be subtracted from the bolt's available force to withstand high impact loads. If the front bolt is tightened hard against the stop and not against the rear bolt, the rear bolt could loosen during the impact loads."
Recommended torque values have been set in the product sheet to 60 inch lbs for each bolt.
A warning in the product sheet cautioning that if the clamp lip touches the tube, the seatpost could dimple during clamp tightening.
Another warning that post is for use with 7mm seatrails only.
Thomson says : "The Thomson seatpost design incorporates a bending fuse to prevent catastrophic failure. All brand-x seatposts we tested - every one of them - failed in catastrophic failure with the seat and clamp components - and sometimes pieces of the tube and head - flying off in all directions. This type of failure would dump the ride."
What stumps me is that for all that marketing on their website, there is actually no bending fuse description on the instruction sheet. I'd actually like to see a description of this and how it works. Is this incorporated into the top and bottom clamp design somehow, and not mentioned? What say, Thomson?
Finally, the highlight of the Thomson marketing is this statement :
"The Thomson seatpost has a clamp, head, and upper tube strong enough to withstand 350 foot-lbs of torque. The tube will start to yield and bend at the seat tube clamp at about 250 foot-lbs of torque. Remember all brand-x posts we tested flew apart at less than 150 foot-lbs of torque. Under severe impact the Thomson seatpost would bend slightly and allows the rider to come to a safe stop or finish the ride. The ride could continue."
My thoughts on this statement are that putting this alongside with what was actually observed by the user who broke his seat post (see top picture of failure), the tube did not withstand the force and there was no observation of bending. It appears that the impact forces approached ultimate strength for the broken area in question and broke catastrophically. It looks like the rider was not injured in any serious fashion.
What remains to be researched is how the bike with the seat post and saddle fell, validate the claims of the user (see above) when he replied that he did not overtighten any of the two bolts, validate the claims of the presence of a bending fuse and the actual strength of the product from the manufacturer, do a small paper and pencil analysis of the forces and stresses encountered and compare this with known the known design limits of the seat post.
The owner has made it known to us that for about a year, he did not have to change the saddle on the seat post. It is likely that during this time, he may have lost notice of the critical areas of the seat post. A stress riser may have led to the formation and propogation of a tiny crack, which, upon the post striking the ground in this fall, led to the severing of one of the bolting spots from the tube due to the torsional shear stresses encountered.
What was nice from writing this post so far has been the fact that this issue has been exposed to the world. Users must remain careful of how they install and use cycling products. At the same time, competition in the cycling industry is cutthroat. Over the years, we've seen an increasing number of bad designs with bold marketing claims and promises. Few have stood the test of time.
UPDATE APRIL 12, 2009
A reader notified me of another Thomson seatpost failure incident, only this time it was a setback post and the failure occurred on the post body itself, very close the bolting ears. These pictures were shown on Mtbr.com Forums, by user Apacherider. Incidents like these are not safe and opens up a range of possibilities for injury. Since the above incident and this new one is not very far apart in occurence date, Thomson must really dig into the backgrounds of the causes. It seems to me as if these posts are in need of more reinforcing in the areas around the bolting ears, including the ears themselves.
