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Technical FAQ: Are bottom bracket threads backwards?

  • By Lennard Zinn
  • Published Mar. 4, 2014
  • Updated Oct. 30, 2014 at 5:34 PM EST
Yes, some Dura-Ace crankarms can work with Ultegra arms, and no, bottom bracket threads aren't backwards. Photo: Caley Fretz | VeloNews.com

We continue to receive compatibility questions related to 10- and 11-speed drivetrains, so we’ll address a few of those here, as well as one reader’s question about bottom bracket threading. We’ve also received some feedback on last week’s helmet cam column and we’ll run it here.

Are bottom bracket threads backwards?

Dear Lennard,
The way the bottom bracket thread standard is, it would cause a bottom bracket cup to loosen when pedaling if a bottom bracket bearing gets too tight. It seems that if the drive-side is right-hand thread and the non-drive-side is left-hand, then the pedaling motion will not cause the cups to loosen. Did someone got it wrong originally or is there a good reason for it? Luckily bottom brackets are becoming threadless.
— Ned

Dear Ned,
Actually, the English standard bottom bracket threads are set up correctly. When the bearings are functioning properly, pedaling tightens the cups in. When the bearings are seized up, pedaling would loosen the cups.

If that’s not clear, then think about it for a moment. The drive-side cup is left-hand threaded, so if the crank were affixed to the cup like a wrench (as would happen if the bearings were seized up), pedaling forward would turn the cup clockwise, which would unscrew the left-hand-threaded cup. But if the bearing turns freely, then the spindle turning clockwise rolls the ball bearings along with it, and the outboard side of each ball turns the opposite direction of the inboard side of the ball. So, the free-rolling balls are tightening the cup in further as the rider pedals forward.

The inverse is of course true for the non-drive-side cup. And pedal threads behave the same way, even though the drive-side pedal is right-hand thread and the non-drive-side pedal is left-hand threaded.
― Lennard

Will my 10-speed chain work on an 11-speed crankset?

Dear Lennard,
I am running a 10-speed drivetrain for next season. Might be either SRAM Red or Shimano Dura-Ace. I have both kits and am building up a new road bike.

I do need a new crank. The new Dura-Ace 9000 crankset looks great. I was looking at the 50×34 compact version.

How do you think it will work with a 10-speed chain? Does it require an 11-speed chain? If so, will my 10-speed rear derailleur, cassette, etc. work well with an 11-speed chain?
— Peter

Dear Peter,
You can use a 10-speed chain on that Dura-Ace 9000 crank without any problem.
― Lennard

Can I use one Dura-Ace crankarm and one Ultegra?

Dear Lennard,
Can I use the Stages Dura-Ace 9000 left crankarm on an Ultegra 6700 crankset (same 175mm length)? I would just swap the left crankarm from one bike, which has the full Dura-Ace, to the other bike, which is all Ultegra 6700.

My query is because I wanted to be sure there will be the same distance/offset between the bottom bracket and the pedals on both sides; it looks the same visually.

I believe this is the “Q” factor — I can find some figures for the older Shimano models but none for the 6700 and the 9000, and the older ones did differ. I just want to be sure both left crankarms have identical Q-factor?
— Grahame

Grahame,
According to Shimano, the FC-9000’s Q-factor is 114.8mm and that of the FC-6700 is 115.4mm. That’s essentially the same. It’s hard to imagine anyone could even feel a 0.6mm difference in Q-factor; that would be only 0.3mm per side! I also checked in with Stages and marketing manager Matt Pacocha’s answer is below.
― Lennard

Answer from Stages:

All of Shimano’s Hollowtech II road cranks (save for the triple configuration) use the same interface and stance-width (Q-factor), thus they’re interchangeable without rider repercussion. Of course, there is an aesthetic difference, but mechanically there is no issue … save for retrofitting the Dura-Ace 7800 crankset; the issue here is that the bottom bracket spindle is not drilled for the safety catch (little plastic hook found between the pinch bolts) used on the contemporary cranks.
— Matt Pacocha
Marketing manager, Stages Cycling

Can I use Dura-Ace rings on an Ultegra crankset?

Dear Lennard,
I have obtained some Dura-Ace 9000 compact rings to fit on my Ultegra 6800 cranks and although they fit ok, the “shoulders” of the large chainring and the crank are not quite the same; the DA is shallower. Does Shimano, or yourself, have views on using DA rings on Ultegra cranks? I wanted a 50×36 setup for three weeks climbing in Gran Canaria. I don’t want to damage the cranks or rings.
— Chris

Dear Chris,
The chainring relief not lining up with that of the crank spider arms is an aesthetic issue, not a functional one. The chainrings will work fine. Shimano’s four-arm asymmetrical 110mm BCD bolt pattern on Dura-Ace 9000 and Ultegra 6800 cranks is the same.

Interesting to substitute Dura-Ace chainrings on an Ultegra crank, since the Dura-Ace chainrings are more than double the price of the Ultegra rings. But I suppose that Ultegra 6800 rings have only recently become available in the aftermarket.
― Lennard

Feedback on helmet cams

Dear Lennard,
I saw your recent column on helmet cams, and I’ve always wondered how they might affect the performance of the helmet in a crash. To me, mounting anything on a safety device that is not proven to enhance safety is an inherently bad idea. I don’t need empirical data to tell me that there is at least some risk there with no upside payoff. On the other hand, folks have been mounting lights on helmets for a much longer time, and that would appear to create similar risks. However, at least there’s a safety trade-off of better lighting.

Sure, it’s cool to be able to post your race/ride on YouTube.com, but I think the only real benefit to cameras on bikes is for post-incident protection in court or in an insurance claim after a crash or being harassed. Whatever the reason, the camera works just as well (or better) mounted on the handlebars and/or under the seat and poses little/no safety concerns when mounted there.
— John

Dear Lennard,
I was disappointed in your article on the potential for helmet cams to cause catastrophic helmet failure and lead to serious head injury. I’m a neurosurgeon, so I have experience with head and neck injuries. I’m also a mountain biker and road cyclist, with personal experience with cycling injuries (both in myself and my friends). The capabilities and limitations of various types of helmets have been well established in scientific studies. We know they confer some protection, but there are limits to their protection. With a hard enough impact, any helmet will fail.

The possible association you mentioned between the use of helmet cams and serious crashes is just that: an association. By concluding that helmet cams are responsible you are suggesting to your readers that correlation equals causation. This is the same logic that says that umbrellas cause rain. Maybe riders with helmet cams take more risks and therefore crash more often? If someone’s shredding with a helmet cam running I think they’re going to go big; they’re not recording an easy spin.

Your writing has always been sensible and grounded in experience. I know you’re not a scientist, but please don’t discourage your readers from using a modicum of skeptical thinking.
— Richard

And, since the Polar Vortex seems to still be hanging around

Dear Lennard,
We’re having a brutal Arctic winter in Southern Ontario. On the plus side of being kept indoors, I’ve been giving my bikes a more thorough cleaning and tune-up. A couple of items overlooked in the past, I thought might be worth sharing with fellow Tech FAQ readers.

For a couple of seasons, I’ve heard a kind of creaking sound from my brakes and feeling slight but perceptible friction, particularly the rear. I first thought one of the housing sections had burrs. The “irritation” persisted after I removed, reamed, and reinstalled the housings. I finally isolated the noise/friction to the caliper itself (Shimano 7800). The culprit was the end of the return spring where it runs inside a plastic bushing. So now, in addition to lubing all the pivot points, I squirt a couple of drops of Finish Line Teflon Dry Lube in the bushings. My brakes have never been smoother!

My Cervélo RS has a replaceable rear derailleur hanger, as many bikes now do. I was surprised to find the two mounting bolts had loosened. The pressure of the skewer helps to keep things tight, but loose bolts could cause some loss of shifting precision. A couple of drops of Loctite should prevent recurrence.

So I’ve added these two items to my maintenance checklist. Hope this helps others.
— Bernard

FILED UNDER: Bikes and Tech / Technical FAQ TAGS: / / /

Lennard Zinn

Lennard Zinn

Our longtime technical writer joined VeloNews in 1987. He is also a framebuilder, a former U.S. National Team rider, and author of many bicycle books, including Zinn and the Art of Mountain Bike Maintenance 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. He holds a Bachelor’s degree in physics from Colorado College. Readers can send brief technical questions to Ask LZ.

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