Technical FAQ: Carbon in cold conditions

Chilled Carbon

Dear Lennard,
I read your “Carbon in the Sun” article. In my “subjective” experience, cold cycling (leaving it in the garage over the winter) a carbon frame can cause damage. I noticed the stiffness decrease in my Trek carbon fiber frame after one year of use. I asked a composite expert at Ball Aerospace about this and he said that “micro-cracking” in the composite matrix can occur if you cold cycle the carbon fiber. Micro-cracking will decrease the stiffness properties of the matrix.
Kraig

Dear Kraig,
I checked with Neal Haas, an engineer at True Temper’s research facility in San Diego. He used to work in the aerospace industry before working for True Temper and is an engineering genius. He said:

“CF (carbon fiber) components are used extensively in launch/reentry vehicles and satellites where the temperatures range from superheated to near absolute zero. The ultra low CTE (Coefficient of Thermal Expansion) of carbon fiber make it ideal for these temperature extremes. I find it very hard to believe that a bicycle sustained damage during winter storage in a cold garage – regardless of the earthly location. I have seen “green” (not fully cured) paints and top coats crack in extreme temperature conditions but never a CF composite structure.

The expert at Ball Aerospace is correct regarding micro-cracking but failed to mention that only micro changes in stiffness would result. The modulus of resin is significantly smaller than the modulus of CF. Therefore, slight degradation of the resin, while real, would be difficult to measure on a test fixture and would probably be imperceptible to the rider. Additionally, the resin comprises only 20-33 percent of the structure while 65–80 percent is CF. At this point you’re starting to multiply a lot of small decimals together ─ and the drop in stiffness is going to be very, very small.

As far as safe operating limits ─ I would worry more about high temperatures than low temperatures as the resin commonly used in sporting goods will slowly start to break down over a long period of time at temperatures above 220 F. I wouldn’t recommend riding in active volcanoes, reactor containment buildings or too close to the sun.”
Lennard

Servicing the unserviceable

Dear Lennard,
Couple issues with my ’97 Santana Arriva tandem involve the component group. It came with Shimano 105 STI 8-speed mixed with XT/XTR derailleurs. We wore out the right shifter with all those extra gear changes one makes on a tandem. Santana recommended moving to a 9-speed group as an upgrade, because the shifters are not serviceable. I mixed Ultegra and XTR 9-speed and got things working at some expense, but the front derailleur adjustments are more touchy and a bit frustrating, while the old 8-speed was a bit simpler. Then I learned very recently that my LBS routinely repairs STI shifters. Are the mechanisms really serviceable? My understanding and recent experience is that Campagnolo is easily repairable (that little spring, so expensive yet so nice to have working again), while Shimano STI is not. And what is the simplest way to get the 9-speed Ultegra shifting and trimming just right?

Finally, a lengthy and involved dumpster salvage job on a ’70s Motobecane has me applying 28 percent aqueous ammonia in a little meniscus at the stem to steel interface at the top of the fork tube to free the stem. It’s really frozen. The stem bolt loosened with a couple of gentle taps. My colleague recommends replacing both stem and ‘bar when I get it free. What is your opinion on the chemistry approach and the replacement?
David

Dear David,
If your shop can overhaul a Shimano STI lever and make it work again, bring it to him and see how it works out. Shimano strictly recommends against it. Those levers are completely assembled by robots, and any mechanic who can duplicate that work is worth his weight in gold.

I took a broken Ultegra 9-speed STI lever apart once with the intention of fixing it. I believe it is still in pieces in a box in my attic. I remember having to make a number of tools to disassemble and reassemble it. I also remember encountering a lot of springs that were hard to wind up during assembly.

As for tips on tuning your front derailleur, I’d need to know whether you have a double or triple crank. But since every Santana Arriva tandem I’ve ever seen comes with a triple, I’m going to hazard a guess that you have one. And I’m going to hazard a further guess that you are a lot taller than your stoker.

Tandems that are built for a tall captain and short stoker often have a high bottom bracket for the stoker. This is to avoid either minimal seat post extension for the stoker or a steeply-sloping top tube, which would result in a lot of seat post extension for the captain. By raising the stoker’s bottom bracket (and making the captain’s bottom bracket as low as possible), the top tube can have a gentler slope to the back while keeping the seat post extension more within a normal range for both riders and raising the stoker up enough to be able to see over/past the captain more easily and not have her/his nose pressed against the captain’s butt.

So what does a high stoker bottom bracket have to do with front derailleur adjustment? Quite a bit, actually. Triple front derailleurs have a lot of shaping of the inner cage plate. There are different grooves pressed into the steel plate for the groove to ride in while it is on each of the three chainrings. These grooves are located quite precisely, and the sections between them that protrude toward the chain help lift the chain when shifting to a larger chainring. However, the higher the bottom bracket is, the more chain will be angled downward toward the cogs rather than up toward them as with a standard road bike bottom bracket height. So, if the bottom bracket is significantly higher than Shimano had planned on when designing that front derailleur, the chain, by angling downward more, will rub on the upper corner of the inward-protruding sections of the inner cage plate. It will be exceedingly difficult, maybe even impossible, to adjust the front derailleur to shift properly and not rub on the chain in the slightest of cross gears.

That’s just a guess about what may be going on with your bike, but if you have a triple, I’d check the bottom bracket height as well as look for exactly the kind of rub on the raised spots of the inner front derailleur cage plate that I described. If you do have that problem, there is a fix: an FSA front derailleur. FSA came out with its front derailleur when it first introduced compact double cranks, because standard double front derailleurs were not very effective at shifting on them. It has no bumps on the inner cage plate, and the tail comes down low enough to clear the chain coming off of the granny chainring (on a bike with a high bottom bracket). I’ve found it to be a great front derailleur for bikes with a triple and a high bottom bracket. At Zinn Cycles, we have a lot of experience with this problem, because we build so many frames for tall people using uncommonly long cranks – 200mm to 220mm – that have correspondingly high bottom brackets. We used to equip a very high percentage of these bikes with triple cranks (less often now that road double rear derailleurs have much greater gear capacity), and we could not find any triple front derailleurs that would work.

And regarding using ammonia to free your stem, that is a good solution. I wrote a column about freeing a stuck seatpost last October, and much of the mail I got on that was about recommending ammonia rather than penetrating oil (which dissolves steel rust but not aluminum oxide) as well as some other methods of rapidly cooling the part besides discharging a CO2 inflator cartridge as I had suggested. Here are some of those letters.
Lennard

Freeing the frozen

Dear Lennard,
Ammonia dissolves the corrosion between AL and steel very well. (Liquid Wrench does not work). I assume it works with Carbon and AL, but I’m not really sure.

I’ve freed a stuck stem using liquid Nitrogen. As you know it is much colder then Ice, and is easily available from any university physics department ─ one just needs to find a bored grad student or cyclist in the department. Since the coefficient of expansion of AL is much greater than Steel, the AL part will shrink significantly more than the Steel (I think it was over 0.002″, but may have been significantly more ─ should redo the calculation).

Dry Ice is also pretty cold and easy to get.
Greg

Dear Lennard,
Next time, try straight ammonia for stuck aluminum parts. The ammonia dissolves the aluminum oxide. I know it works for stuck aluminum quill stems in CroMoly forks, and I’d bet it will work for aluminum seatposts and/or carbon seatposts stuck in aluminum frames.
Larry

Dear Lennard,
Just thought I’d point out that I’ve seen several carbon frames damaged by sweat corrosion from wind-trainer use.

Seatposts have been stuck into frames, but also top-tube cable stops have oxidized and busted clean off, requiring re-gluing/riveting and leaving unsightly bubbling of the top coat of lacquer.

I can’t stress enough to my clients that any bike being used on a wind-trainer needs frequent cleaning with clean water, and it pays to whip the seat post out every now and then.
Oli Brooke-White
ROADWORKS /Jazz Apples Cycling Team

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