Friday, March 5

Composite Questions Answered

Y'all are certainly a curious lot. Rather that attempt to comment back at all the questions, I'll do this post where I deal with them all at once. Some of them will be treated further in future posts. One prompts an addition to the agenda. Anyway, here goes, from newest to oldest, grouped by post.

In "Aero Diversion," Rantwick opines "experts in complex topics" meaning someone other than himself.

REPLY: This from the only known human to capture a half-breed Yeti on video in the wild. It's like Tex Johnston passing himself off as an ol' country boy.

In the same post, Whareagle speculates that "Yeah, but if Kelly Johnson had had access to the composites that are now available, don't you think he would've made the thing 'Leak-Proof' by using composites throughout the infrastructure?"

REPLY: Whareagle, I don't think you are advocating that we make bike frames 'leak-proof' so that we can use them to go to the gas station in order to fill our frames up with gasoline for the lawn mower. Seriously, carbon is an attractive material not because it is inherently more "aero." A lead casting can be aero. It is not attractive because it has low density. Magnesium has low density. It is not attractive because it is strong, or stiff. There are alternates that provide either of these more than carbon. It is attractive because of the combination of ALL of these. If it was simple, all bikes would be the same!

In the same post, Anonymous wonders "Perhaps the real question is not Aero or anything else 'speed related' but longevity."

REPLY: I will treat this at more length in the "corrosion" and "sun" that are three and four posts away in the series. However, I will note that properly cared for, there is no reason that carbon composites cannot outlast your grandchildren if you are old enough to read this post. There are a LOT of 1953 Corvettes in prime condition around and carbon is much more durable than the fiberglass cloth used in those. Likewise, today's resins are better as well.

Anonymous also wonders in the same comment "do composites really represent the best value for the typical (non racing) cyclist?"

REPLY: This will also be explored in more detail in "Carbon Weight Myths, Legends, and the Truth." My personal opinion, however, in a nutshell, is "no." Bikes, however, are not entirely about the "best value." There is cachet to having carbon on a bike that goes beyond pure value. What's more, non racing cyclists represent a huge spectrum, and some carbon items represent much better values than others, and not always for the obvious reasons. My SRAM Rival brake levers are, for example, carbon. I am very glad they are carbon and not aluminum when I first touch the levers when it is 107F outside or below freezing. THAT has little to do with weight or raw performance. Plus they look REALLY cool!

Finally, polishing off the comments in THAT post, Big Oak looks forward "As carbon technology continues to develop, it'd be interesting to have a glimpse...into the future."

REPLY: Good Point, add "Today's Technologies on Bikes Your Kids Will Ride" after the Lance post. In truth, there are many existing composite technologies that have not yet found their way onto bikes, but they will. I will leave pure speculation to others, but bike designers have many untapped elements in composite technology still to explore.

In "How Composites Work," Ron inquires "Its interesting you state that that the hole will decrease strength by half but in what mode of loading? Was this stated in literature somewhere or you have this knowledge from experience? Is it any different from the behavior of metals? For example, the stress concentration of a .125" transverse hole in a 1" OD .5" ID tube for bending is about 3.11, so factor of safety decreases approx. 33%."

REPLY: Tension, Yes, Yes, Yes (profoundly so- look again at the last table in the post), Factor of Safety does not decrease. Factor of Safety is a design criterion. MARGIN OF SAFETY would decrease. I may need to add another post for techie types reading this, though some elements will be in the experimental stress and loads posts. That "techie candy" post will be an addendum after the last of the main series and ought to include some references for future study. Besides, Ron, why didn't you ask about "compression after impact?" THAT is the big bugaboo.

In "Carbon for the Rest of Us," Ron notes "So bike manufacturers could do a lot more to help bike mechanics in this area? Meaning they don't? Ha. I wouldn't be surprised. Check my blog out for failures from time to time."

REPLY: Yes, No, OF COURSE you aren't surprised. What's more, we're just getting to the parts of this series where bike mechanics and owners start to see stuff that they can potentially put to practical use. The history and "how they work" posts really are just setting the stage to address the CITIZEN RIDER challenge. I hope I'm not giving too much away to state that "squid magnetometers" are NOT going to make life wonderful for mechanics OR owners. But they really DO sound cool, eh?

HOMEWORK PROBLEM FOR RON
Calculate how many fatigue cycles a chain experiences in 1000 miles assuming you are in your favorite gear and are a spinner instead of a pure "big gear" guy. Ignore the minor cycles where the links change direction as they go around the rear derailleur pulleys. Hint, I would guess it's upward of 250,000 cycles. Now consider what happens to even a minor chain defect after those numbers of cycles. Mainly, why are you still messing with Shimano when there are at least two better choices around, one of them based in the USA? You get used to SRAM and Shimano will never be the same again. Even if you keep the levers and cassettes, SRAM makes chain that works well until you can spring for REAL drivetrain equipment.

4 comments:

Rantwick said...

Who's Tex Johnston? Also, making yourself an expert in something trivial is easy... I know, because I am an expert at it. Hard won knowledge gained through formal education informed by serious experience should not be mocked, even by the self-deprecating.

Ham said...

Actually, I hate to get in ahead of the article (which I'm looking forward to) there is an easy way to compare carbon and alloy bikes in the real world. I just decided not to take over your comments box, and post the story here http://cyclesafeandhappy.blogspot.com/2010/03/carbon-vs-alloy-bikes.html

Steve A said...

Ham is quite correct that at useful levels, carbon/metal comparisons can be made. Of course the question of "value" has a large individual component and that's part of the fun. I look forward to the twists and turns of this story as he blogs about it. As long as an Axiom carbon rear rack doesn't figure into it!

cafiend said...

I've used SRAM chains since they were Sedisport. I've disliked Shimano chains for just as long. Then the Hyperglide pin issue just sealed the deal.

Shimano uses the nicest-smelling packing grease, though. I love to smell a new Shimano chain as much as I hate to install it for the poor marketing victim who insists on having it.

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