January 16th, 2012

The Perils of Progress

Bikes are getting lighter; but when we lose weight, we lose other things too.

By Joe Lindsey

Stay with me here this week; the Report is going all over the place.

Today I’d like to depart from talk of bike racing and talk about bikes. (If the Boulder Report is the primary place where you find my writing, you might not realize that I test gear for the magazine too.)

How long I’ve been doing it isn’t really a big deal, but if you’re curious, let’s just say that when I started, reviewing a lugged steel bike wasn’t a special occasion. But in the last three-odd years, most of the road bikes we review at Bicycling are carbon fiber, and an increasing number of mountain bikes are, too.

As carbon has come to dominate, we’ve seen an explosion of innovations that make bikes lighter, stiffer under pedaling, and generally more fun to ride. And we’ve seen a focus on bringing weights down to previously unimaginable levels.

Not so long ago, there was debate about whether frames could breach the 1,000-gram barrier. Now, that’s pretty common, and the bar is set lower. A Cervelo R5ca will set you back close to $10,000 before you put a single part on it, but it’s also 690 grams (video).

Framemakers have achieved this because of increased knowledge of how to work with carbon fiber, from molding simple tubes to complex shapes, like carbon dropouts, which reduce weight.

They do that not so much because the carbon dropout itself is lighter than the aluminum version it replaced, but because you no longer need a reinforced joint for the bond, the overlap of material between frame and dropout plug, and the bonding agent itself.

Carbon dropouts are not only lighter; they’re stiffer because there’s no joint, and they are stronger and less prone to failure than a bonded joint.

But there’s one failure exception—the carbon bike’s Achilles’ heel: damage in shipping, a crash, or from an improperly adjusted derailleur that goes into the spokes and takes the drive-side dropout with it.

If that happens, the frame is either toast or subject to an expensive repair. Damage like this is almost never covered under warranty because it’s not a manufacturing defect, but angry customers with trashed frames do not make for repeat sales, so bikemakers try to prevent it from happening.

They do that by engineering the failure into a part before it reaches the frame. That’s when you get this:

Soft derailleur hangers break easily.

“This” is a broken derailleur hanger. They’re quite a bit more common than they used to be. Said hanger was formerly on a test bike. Which company’s bike doesn’t really matter, because there’s not a lot of difference these days in how bikemakers approach the issue of how to protect possibly fragile carbon dropouts.

As carbon dropouts have proliferated, derailleur hangers have increasingly been made of very soft aluminum. How soft? Have a look:

Scalloped indentations from QR skewer.

Those indentations are from the quick-release skewer clamp. Like roughly a third of the carbon bikes I’ve tested in the last couple of years, this bike had a bent hanger when I pulled it from the shipping box. Because of that ratio, I actually now own a Park hanger-alignment tool—the sort of tool that consumers can buy but which is mostly found in shops.

After I gently straightened it, the hanger held for a couple of rides but I knew it had been weakened; aluminum doesn’t respond well to lots of bending. (Note that the break is right where the hanger thickness changes. It’s engineered to fail there, just below the dropout itself.) The bikemaker sent me a replacement hanger (normal dealer cost is $15), which was good, because this one broke as I was unscrewing the derailleur.

The advantage to this is what you see here: An inexpensive hanger functions as a circuit breaker, thus saving the rest of the system expensive damage. Shimano’s Shadow mountain bike derailleurs have a similar feature in the fixing bolt, which is handy when you’re discussing a $100-plus part that also usually gets trashed when you have a shifting failure.

The disadvantages of a weak hanger are both obvious and not. On the obvious level is the fragility of such beasts. If you have a bike with carbon dropouts, do yourself a favor and order at least one replacement hanger at your dealer. They’re inexpensive and a good item to have on hand.

But there’s a sneakier disadvantage that remains even if the hanger serves a long and faithful life: shifting quality.

Weak hangers flex minutely under load when downshifting, especially under power. If you ever wondered why your bike shifts OK on the stand but not on the road, or have been unable to dial in even a new system and alignment isn’t a question, your derailleur hanger could be part of the problem.

(Aside: Another trend among bikemakers—the return to the internal cable routing craze—can also be a culprit because of the increased friction. Dear bikemakers: Unless it’s an aero road or TT bike, rout cables outside the frame! Internal routing is a pain in the ass, and I hope this trend dies as fast as it did the last time around.)

There’s one very good solution for this: An aftermarket hanger from a company like Wheels Manufacturing. Wheels’ hangers are made of 6061 aluminum, substantially harder than the soft alloys used on OEM hangers. It’s hard to believe something so simple could change shifting performance, but it can. This is not an advertisement for Wheels; they’re simply the most prominent and easily found replacement hanger in the U.S.

Of course, since they’re harder, you want to think about the risk of damage you might incur. If you race criteriums, you’re more likely to crash than most and less likely to be downshifting under load. The 6061 alloy used on most replacement hangers isn’t the hardest aluminum (that’s 7075) so it may protect your dropout, but not as well as the stock hanger. If that’s a major concern, maybe you can get by with the stock hanger.

Whatever hanger you go with, If you fly with your bike I recommend unscrewing the hanger along with the derailleur. For cases that require you to remove the rear wheel, use a firmly attached rear dropout block spacer and liberally pad the dropouts themselves (and, of course, the derailleur).

(Second aside: The best dropout spacers I know can be made of a simple length of 10mm diameter threaded steel rod with four washers and four wingnuts. Probably $10 total at a hardware store. They stay put far better than the cheap plastic spacers used to ship many bikes.)

There’s no single answer here. Carbon dropouts require a bit of extra care. But how you handle it is a choice that requires some level of compromise: protecting your investment at some cost in parts damage (derailleurs aren’t cheap) or shifting quality; or get the best performance and risk potential frame damage. Or buy a metal bike. Progress is hell.

This has been an unscheduled Boulder Tech Report. Please stay tuned. There might be more.

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    Great post.

    One comment: if you’re racing crits, or just racing, consider a frame like a Specialized Allez E5 or a Cannondale CAADx (whatever # they’re up to).

    They ride great and they’re relatively cheap. Slap a decent rear mech hanger on ‘em and you’ve got a frame that shifts right.

    ANd . . . internal cable routing is evil–unless the cables are for electric . . .for itiarit

    Thanks Joe – I too hope the internally routed cable idea dies off as quickly as it has in the past. Some of the pro teams have had steel hangers made to improve shifting as shown here http://www.bikeradar.com/news/article/tour-de-france-tech-looking-through-the-magnifying-glass-30925/
    but of course if their bikes get wrecked replacements are free!
    My advice is get a spare hanger and make darn sure your low-gear limit screw is dialed in. For shipping a bike I find removing the rear mech to be enough while a piece of small diameter PVC pipe cut to 130 mm and secured between the rear dropouts using the rear wheel skewer works well to protect things in the back.

    [...] The Perils of Progress Weak hangers flex minutely under load when downshifting, especially under power. If you ever wondered why your bike shifts OK on the stand but not on the road, or have been unable to dial in even a new system and alignment isn’t a question, your derailleur hanger could be part of the problem. [...]

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    [...] here to see the original: Perils of Progress: Carbon Fiber and Other Challenges This entry was posted in Bicycling.com by Donald. Bookmark the [...]

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