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Technical Q&A with Lennard Zinn – Recycling carbon and other follow-up

Dear Readers,I’m in the Denver airport about to fly to Italy for the Giro d’Italia. I have enjoyed a lot of the feedback from a few recent columns, and I thought you might as well. Next time you hear from me will be from the Giro, so look for some cool bikes for the team time trial soon. Lennard Feedback on April 29 column .On fixing carbon frames: Dear Lennard,

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By Lennard Zinn

Carbon is a versatile material, both recyclable and repairable.

Carbon is a versatile material, both recyclable and repairable.


Dear Readers,
I’m in the Denver airport about to fly to Italy for the Giro d’Italia. I have enjoyed a lot of the feedback from a few recent columns, and I thought you might as well. Next time you hear from me will be from the Giro, so look for some cool bikes for the team time trial soon.

Feedback on April 29 column .
On fixing carbon frames:

Dear Lennard,
Re: your Q&A on repairing carbon frames, I was hit by a car last year and my top tube was cracked. I sent the frame to Calfee and it was repaired in a few weeks. It looks nearly perfect. It cost me $300. The repair person also told me he could wrap the bottom bracket to stiffen the frame up for a bit more. Overall, Calfee was a God-send. They saved me money and gave me a solution for stiffer frames down the road. Good people.

Since then I have told people about the repair. It is interesting that people think that once carbon is cracked, it’s trashed. Not true.

Feedback on April 15 column .
On air compressors:

Dear Lennard,
Sears sells a dandy wall-current electric compressor that doesn’t have a tank, it just pumps air directly into its hose. It has a pressure gauge built in, I’m not sure how accurate, but it seems close enough. The fitting on the hose end is a clamp-on Schrader fixture, but you can get a brass Schrader-Presta adapter that screws onto the Presta valve stem. REI has them, and I suppose most any well-stocked bike shop. I wore out one of these compressors in about ten years and bought another, I love it. It’s listed at $55 on Sears’ web site. Click “Tools,” “Compressors and Air Tools,” “Air compressors and Inflators,” and it’s the Craftsman 120 volt Air Compressor Inflator.

Dear Lennard,
I saw the question about affordable compressors. I think you may have missed something. I am currently using a $15 compressor made by Bell in my car. It plugs in to my lighter socket, has a pressure gauge and quickly gets my tires up to the needed 110 psi. I think I got it at Wal-Mart. Am I doing some thing wrong? Now if I could only find one that plugs in to a wall. It makes a great yet slow emergency pump for when my truck flats.

Dear Lennard,
I have used the Campbell Hausfield Cordless Inflator for years to pump bike and car tires. It is rechargeable and at 11 X 9 X 4 and weighing in at 12 pounds, very portable. It contains a very accurate pressure gauge and has proven to very reliable. It’s available at an orange colored big box hardware store for $39.97.

On stationary trainers:
Dear Lennard,
Just a quick follow up on carbon bikes…people who are sweating buckets all over their bikes aren’t using a trainer properly, every trainer should be used in front of a huge fan.

Carbon fiber is the only frame material that can be fixed to strength equal to, or better than new. You can’t do this with any metal.

From an environmental perspective, it takes a tremendous amount of energy and pollution to mine, smelt and purify the alloys in any metal bike frame. Carbon fiber frames can be built with fibers originated from natural sources, such as flax, or even carrots (curran). Here’s an interesting news item on that topic.

Dear Lennard,
In your April 15 tech column you wrote:

“Furthermore, the danger of corrosion from sweating on a bike on a trainer is an issue with a steel, aluminum or magnesium frame, but it’s generally not with carbon.”

I have a 2001 Trek 5200. I’ve used it on a trainer many times. With the thought that carbon was corrosion proof, I never worried about protecting the frame from sweat. A few years ago I noticed that the brake cable housing braze-on (if that’s what it’s called on a carbon bike) at the front of the top tube was beginning to crumble. By the time I noticed, it became impossible to save. It came off, along with some of the clear coat where it was attached.

No it’s not the carbon material corroding, but it’s good to keep in mind that a carbon frame has non-carbon attachments that are susceptible to corrosion and should be wiped down and/or protected from sweat and the elements. I now run a full length of brake cable housing along the top tube held in place with zip ties. It’s time for a new bike, anyway.

P.S. Thanks for your always informative column…and your line of tall clothing. (I’m 6-4)

Dear Lennard,
I wanted to tell you about my experience with doing workouts on the trainer and the stresses that a bike goes through. Based on my experience I have to disagree with your comment that “While the stresses are different on a bike constrained to a trainer than on the road, they are nonetheless far smaller than the kinds of stresses commonly encountered when riding on the road.”

A bike being ridden on the road is free to sway back and forth unencumbered during sprint workouts. If you take the same sprint effort and apply it to a bike that is attached to a trainer that locks onto the rear skewer you are forcing the dropouts of the bike to handle all of the back and forth swaying of the bike that is generated during a sprint which usually is not a factor on the open road. This is just like using a lever to pry up a large rock. The lever in this case is the chain and seat stays with the rock being the attachment mechanism of the trainer. When the bike is forced into its flexing state from a sprint workout on the trainer the force generated has to go somewhere. This is the most typical cause of rear triangle fractures on road bikes.

I have a frame at the house that I can show you if you would like with this type of fracture on it.

Feedback on April 22 column .
On carbon recycling:

Dear Lennard,
I saw your tech column today about carbon fiber recycling. Eric Lombardi is mainly right that carbon fiber isn’t recycled today, but it can in fact be done. I’m actually writing a grad school paper about aircraft recycling right now, and there’s going to be a large demand for being able to recycle carbon fiber in a few decades (think the new A380 super-jumbo at the end of life). I’ve attached a recent paper on the state of CF recycling technology. There’s a few processes being studied right now, two of them being mechanical grinding and pyrolysis. Grinding basically just produces filler for stuff like new plastic park benches. Pyrolysis is a bit more interesting, you’re basically heating the material in an inert atmosphere, so it more “evaporates” than burns. You can actually extract the carbon fiber and an oil-like liquid that can be used as fuel or as a chemical feedstock.

We’ve found a firm in the UK recycling commercially already: . I thinks it’s going to be a while though until this makes it to consumer products though, but it won’t happen until people demand it. Or extended producer responsibility legislation makes producers deal with the products they manufacture. In the EU for example, car companies are responsible for the disposal of everything they build!
Alex Vaivars
Pedro’s Inc.

Dear Lennard,
Carbon composites are indeed being recycled. In fact these guys will take your scrap for free.
Richard McAinsh
Technical Director, 3T

Dear Lennard,
Regarding recycling carbon fiber, here is a “sustainable” race car. “sustainable” race car.

Dear Lennard,
I went ahead and did a little research and found there are in fact multiple companies who specialize in carbon fiber recycling. Of course the much larger aerospace industry remains the primary customer of such technology but I can only hope it’s a matter of time before the bicycle industry follows suit. This link might be of interest to some.

On tube butting:
Dear Lennard,
I read with interest your response to Todd’s question about the relative merits of butted vs. straight-gauge titanium tubing. Overall, you provided a lot of useful information, but one of your examples is flawed. Here’s the passage I’m referring to:

“A butted tube, however, is less stiff than a straight-gauge (continuous thickness) one.”

True enough.

“Grab a yardstick (or meter stick) at the ends and flex it. Notice that the majority of the bowing happens in the center of its length, not at the ends. That’s what happens in a tube as well.”

Here, you have ignored how the tube/yardstick is constrained. The yardstick in your example is simply supported?that is, it’s free to rotate at both ends. The very ends of the yardstick (where you’re holding it) have no bending moment applied to them. Rather, the bending moment increases linearly as you approach the center of the yardstick from the ends.

A bicycle tube is not free to rotate at either end. This is a critical distinction. The “majority of the bowing” does not happen in the center of a bicycle frame tube. If we agree to call maximum angular displacement “the majority of the bowing,” the majority of the bowing happens closest to the constraints?in the case of a bicycle frame, at the tube junctions. That’s where bending moment is the highest.

So you really can’t compare a yardstick to a bicycle frame tube with any degree of accuracy?it’s a flawed analogy.

The question of whether butting is worthwhile isn’t easily solved with thought experiments. It’s true that a butted frame will be more flexible than a straight-gauge frame (given the same tube diameters and max wall thicknesses) but how much more flexible is unclear. Finite element analysis is a great way to answer questions like these. I’ve modeled my steel Ritchey (though the model has straight-gauge tubes, not butted).

The maximum strain under a 1700N load is really quite small and happens mostly in what would be the butted parts of the tubes. I’m making the following numbers up, but I imagine most riders would accept a frame that’s more flexible by 1 percent in exchange for a 100 gram weight savings.

Feedback on 11-speed chains on 10-speed chainrings from November 25 and December 16:
Dear Lennard,
Maybe this is old news by now, but I took it upon myself to be a test monkey for you. I feel it was my duty after you, or more specifically your free custom size dealy thing on your website finally got me comfortable on my bike.

I read that some guy was having a problem with his chain jamming between the chain rings and was blaming it on you, and your advice that mixing and matching 10 speed rings with 11 speed chain was okay. Well I finally figured out how he did it. I’ll bet his front derailleur was poorly adjusted…specifically too high.

I was able to replicate the jamming when I left my front derailleur alone and I went from a 53 to a compact 50. After the jamming took place I looked at the front derailleur and presto it was no thin dime between the lower edge of the front derailleur and the big ring, but more like a .75 cm. Ha! I did it, and I’ll bet if you do that too you’ll get it to jam.

Technical writer Lennard Zinn is a frame builder (, a former U.S. national team rider and author of numerous books on bikes and bike maintenance including the pair of successful maintenance guides “Zinn and the Art of Mountain Bike Maintenance” – now available also on DVD, and “Zinn and the Art of Road Bike Maintenance,” as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.”

Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn. Zinn’s column appears here each Tuesday.