Thursday, March 18, 2010

Jobst Brandt : Part V

Continued from Part IV

The following correspondence completed my interview of Jobst Brandt. In this final section, I asked him what his opinions were behind being famously anti-helmet. I also dug a little deep into the criticisms of his book by experts in the bicycling field and asked him what he thought about some of them.

In the end, I must say it was a pleasure chatting with him. Certainly, a few rapid fire Q&A's will not do justice in coming to understand the kaleidoscope of his bicycling philosophy. So I'm grateful to him for being the patient customer he was for this small period of time and co-operating with me in this wonderful idea.

31. What is your stance on one of the longest running debates in cycling? Pro helmet or anti helmet and why? For sometime now, people have been saying that helmets are inadequate because they do not protect against twisting forces. These days, helmet manufacturers are actively pursuing the design of "anti-rotational helmets". For instance, LAZER helmet has an interesting video and the host is Dr. Ken Phillips who gives an overview of the research he has been doing in helmet safety. Can this appease the complainers?

JB : That is a classic of missing the point, to just look at motorcycle helmets and see what is needed and useful, something that is not applicable to bicycling for the size, weight and lack of cooling. If you look at current helmets, they are a thin mesh of Styrofoam with no structural integrity. The LAZER project is barking up more religious belief trees. The video is a great sham.

I avoid helmet discussions because they are a religious belief. There are no realistic tests and all the people I know who crashed with one received severe head injuries as bad as if they had no helmet - usually skull fractures in the face. In contrast, I and my fellow riders have crashed often and not gotten head injuries other than a scrape that drew a bit of blood.

As I pointed out, Muhammad Ali's glove has far more cushioning than a bicycle helmet, yet it was possible with a mass far less than a human skull for him to deliver knockout punches, protection against which the bicycle helmet is touted.

32. Interesting. You always have some strong reasons behind certain viewpoints, such as the one against helmets. My readers and I were also fascinated by your rationale for choosing yellow paint on your bicycles.

JB : I suppose I'm less fashionable than most people, but I think good fashion is also the most useful design, something we don't see much these days, primarily in the cars and houses we build. The boom-box in cars is a great example of this. Most cars have four exhaust pipes and a lot of other non functional features as it looks and sounds different. Bicycle helmets are a strong fashion statement with their blowing flame shapes like hot rod cars.

33. One of my final questions to you concerns your book The Bicycle Wheel. Can you briefly run us through why you had this work published? Was it out of a strong desire to fill, perhaps a void, in the understanding of the wheel? Or did someone solicit you to write it?

JB : No one solicited anything, with nothing being known about the subject and with the total faith in bicycle mechanics to be doing the build and repair the best way possible. As I mentioned, there was much doubt when the book came out, even from some stodgy engineering professors who felt passed over by a mere bicyclist.

34. The reviews of your book are varied. I believe there are quite a number of people who think that you've done a great service in writing this, others think you're plainly against modern bicycle wheels and expected something more in a book that is titled "The Bicycle Wheel".

JB : The reviews I read gave the impression that I explained about what people want to find... a justification of their expensive "modern" wheels. Meanwhile, the essence of how wheels work and how to build durable ones hasn't changed. It is the website folk who are testy and nasty as thy look for justification of their expensive, unreliable and non metallic wheels, something they don't find in my book. Their criticism is similar to the bicycle helmet advocates who attack anyone who doesn't wear a helmet when bicycling. If you watch you may have seen the videos and stories of collapsing and disintegrating "modern" wheels in racing and touring. I don't want to write a justification of these wheels and dilute the essence of what makes reliable wheels.

35. What about other, more notable critics? Did you ever have a chance to look over John S. Allen's review of your book on Amazon? Mr. Allen is a technical bicycling consultant with an engineering degree from MIT. He's an expert witness and has authored multiple books on bicycles, commuting and repair.

For your convenience, I'll bring that snippet to you. Mr. Allen wrote the following on Amazon back in June, 2005 :
"There is one serious error in Brandt's book, and I am astonished that it has not been corrected through 3 editions. A graph, on page 39 in the 3rd edition, shows the change in spoke tension with lateral loading of the rim. The left spokes are shown to go into compression. They can't, as they simply flex once they are slack. It might also be asked whether this graph reflects the influence of spokes that are differently stressed as the load is applied at the bottom of the wheel. To do so would require a more complicated mathematical model than I think Brandt was able to command.

I also disagree with Brandt's advice to tension spokes until the rim begins to deform. It can then deform further due to increased stresses during riding, and loosen the spokes. I have seen a new wheel which failed after a few miles for this reason. Spokes should be tight, but should leave a margin of safety. If the rim deforms before the spokes reach their optimum range of tension, then they are too thick for it, or it is too weak for them.

I would really like to see this book updated with today's more sophisticated finite-element analysis, including analysis of stresses in the novel low spoke-count wheels. But for people who are willing to build conventional wheels -- the better choice anyway for most cyclists -- this book is a valuable and fairly comprehensive reference. "

Your thoughts?

JB : I recall that item from years ago. I explained that the graph mentioned actually plotted spoke tension of left and right spokes independently and then superimposed the two graphs because they use the same axes, but both do not do what is shown. In fact, part of the continuous curves show spoke compression that does not occur. The purpose was to show the response of spokes to side loads rather than to follow them to the limits evaluated.

I explain clearly in the book that when deformation occurs, the wheel is too tight but that there is no permanent damage that cannot be recovered by reducing tension. It is a method of finding the upper limit without a having a tensiometer.

I found much of his criticism in the same vein as I have heard all along. No one ever wrote about this subject (hence the name of the book) and when some technically minded folk see the book, they feel cheated for not having had the first stone to throw in this forum. They don't say what they would have written or explain what their perception of the stress/strain graphs would have been. They just say what I wrote is mostly wrong and let it ride there. I don't feel compelled to respond to these complaints because they are largely baseless.

As you see, Allen believes the current wheels are "today's more sophisticated FEA" as though mathematics had changed. That's a shot in the dark because it doesn't explain what would be different and why. That is because there is no difference other than the software being more available than when I did the analysis. The results would not be any different.

The book has been reviewed by enough engineering experts to make me sure the analysis is correct. As I said, the critiques are sniping because the implied other solution, the "correct" one is not shown. The reader is left to wonder what the implied correct solution is.

I included reference to Prof. Karl Wiedemer's analysis (Cologne Tech, Germany) in the bibliography. He wrote his finite element work at the same time I wrote the book, and have a pre-print of his technical publication. I also visited him in his home in Siegen and gave him a copy of my book about which we talked at length.

The interview ended here.

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This graph on page 39 of the book The Bicycle Wheel was critiqued by John S. Allen, a consultant and expert witness in bicycle accident lawsuits. These curves show change in spoke tension and the force required to displace the rim and cause these tension changes. Courtesy : Jobst Brandt.

An excerpt from Page 37 of his book on bicycle wheel stiffness should leave some of you with something basic to think about.

"Stiffness, in its various forms, is a subject often discussed by bicyclists with a regard to components as well as frames. Stiff wheels are often mentioned with approval. However, it should be noted that a bicycle wheel is so rigid that its elasticity is not discernible because the tires, handlebar, stem, frame and saddle have a much greater combined elasticity. Therefore, the differences between well constructed wheels are imperceptible to a rider. The "liveliness" attributed to "stiff" wheels is an acoustic phenomenon caused largely by lightweight tires at high pressure and tight spokes with a high resonant frequency. This mechanical resonance can be heard, and possibly felt in the handlebars, but it is not related to the wheel stiffness.

Stiffness is a measure of how hard it is to deflect the wheel, or more precisely, the ratio of load to displacement. Stiffness is not strength. For example, Plaster of Paris is stiff, but not very strong. Since wheel stiffness is so often discussed, the various aspects of stiffness are treated here in more detail than they deserve. Wheel strength, and not stiffness, is the important consideration. If the wheel is strong enough for its intended use, then it is more than adequately stiff.

The terms "stiffness" and "rigidity" are often used when people talk about bicycles. Unless these terms are defined, they are just as vague as the even more popular catchall term "responsiveness". These technical-sounding words can be misleading. Stiffness alone is not the ultimate measure of a good wheel, but rather the balance of stiffness and strength that enables it to carry loads and withstand shocks. "


Jobst Brandt : Part I
Jobst Brandt : Part II
Jobst Brandt : Part III
Jobst Brandt : Part IV
Jobst Brandt : Part V

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