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Technical FAQ: Pedal threads and frame geometry

Lennard Zinn addresses questions about pedal thread direction, compact vs. standard framesets, and more.

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Pedal threads

Dear Lennard,
Why are the left and right pedal attachment thread directions not swapped?

My understanding is that the right pedal screws in clockwise and the left counter-clockwise so pedals will tend to tighten themselves in the normal forward pedaling direction.

My experience has been that bearing friction tends to increase over time and can really increase when they start to fail. So this would tend to unscrew the pedals as bearing friction increases.

What am I missing?
— Theo

Dear Theo,
Good question. Indeed, with the current pedal thread standard, the pedal unscrews if the bearings seize.

Think of it this way: if you have pedals with 15mm wrench flats, you can put a normal pedal wrench on them to unscrew them. Once you loosen them enough to break them free, if you lift the rear wheel, you can unscrew them completely by cranking them in a forward pedaling direction by means of the wrench on the spindle. This is true with both the left and right pedals.

Similarly, once you have gotten the pedal threads started, you can screw the pedals on by turning the cranks backward with the wrench on pedal-spindle wrench flats.

I have seen my daughter twice pedal one of her pedals right off her bike in cyclocross races when the needle bearings in the previous generation of Crank Brothers Eggbeater pedals rusted. She was left suddenly standing there with a pedal attached to the bottom of one foot. I am thankful that the pedal threads were oriented the way they were so that her pedals just unscrewed; she could have injured her feet and ankles if they had been threaded in the direction that you suggest.

Incidentally, Crank Brothers has recognized the potential for these needle bearings (I think they came in 2010-2013 pedals in a number of models) to seize up and offers a fix in the form of the Pedal Refresh Kit. The kit includes a drift punch to drive out the old needle bearings, a pair of Igus Iglide plastic bearings to replace them with, and an improved inboard pedal seal. The Igus bearings can never rust and thus seize up. This is better for pedaling.
― Lennard

Traditional vs. compact frames

Dear Lennard,
I’m looking at a new frameset, and the frame builder offers both traditional and compact frames in the same model. Given that everything else is equal — dimensions, frame angles, tubes, and the joining method — is a rider going to notice a significant difference between the two?

I’m guessing that the compact might feel a little stiffer in the rear because of the shorter seatstays and the fact that the triangle they’re part of is smaller due to the shorter seat tube. But I can’t imagine a significant weight loss, given that you have to use a longer (and heavier) seatpost.

So what’s the deal with the compacts?
— Steve

Dear Steve,
Unless you are very tall, you probably won’t notice much of a difference between the two versions of the same model that your frame builder offers for your custom bike.

The weight loss: the seatstays and seat tube are obviously shorter and hence lighter, and the top tube is shorter and lighter as well, since it is closer to perpendicular to the seat and head tubes (the shortest distance between two lines is perpendicular to both). Everything else weighs the same, and the seatpost is indeed heavier. Not much weight difference except perhaps in steel frames.

Compact geometry does stiffen the frames against torsion, and that can be a big deal for a big rider because it can make the difference between a bike that shimmies at high speed or with the hands off the handlebar, and one that doesn’t. Since deflection of a tube under a given load generally is proportional to the cube of its length, even a 10 percent increase in length results in a 33 percent increase in deflection. The seat tube alone in a compact frame can be 20-25 percent shorter than its counterpart in a traditional frame, so the shorter seat tube, top tube, and seatstays can make a significant stiffness difference. A tall frame can be torsionally so flexible that shortening up some major frame members, thus decreasing the area of those large open space between tubes, can tighten the frame up enough to reel it back in from the realm of being shimmy-prone.

Compact geometry started like many trends in the industry by bike manufacturers (mainly Giant, in this case) who thought they could sell more bikes by offering something different from what was generally available. Manufacturers also like to find ways to get away with offering fewer sizes, and thus lower their production costs, without damaging sales. By taking standover height and a minimal amount of exposed seatpost out of the equation, it is possible to fit a wider range of rider dimensions on a given bike size with compact geometry.

Compact geometry works, marketing-wise, since road consumers have been accepting designs carried over from mountain bikes that they never would have considered 20 or even 10 years ago. Other examples of this carryover are up-angled stems, threadless (and 1.125-inch-diameter and now, tapered) steering tubes, un-smoothed welds, vertical dropouts, disc brakes, and thru-axles. The sloping top tube from mountain bikes has been accepted by roadies, but it probably never could have made the jump from BMX to road bikes without first having gone via the mountain bike.
― Lennard

Feedback on Di2 indicator LEDs

Dear Lennard,
Great article on “Using Di2 Synchro Shift.” One point though. You wrote:

But if you have a Garmin 1000, 820, or 520, you can pair it with your Di2 system via an ANT+ connection, and it will not only show you what gear you are in but will also tell you if you’re in Synchro mode and when your next shift will be a double shift.

I believe you also need to have the SM-EWW01 ANT unit installed as well (or the combo ANT/Bluetooth unit).
— Ken

Dear Ken,
Thanks for pointing that out. I did mention the D-Fly transceiver in the second to last paragraph, and the link I included was to the SM-EWW01 (the ANT transceiver). However, I didn’t read the details of the link carefully. The SM-EWW01 looks just like the EW-WU101, and I had intended to link to the EW-WU101 and EW-WU111 Bluetooth/ANT D-Fly transceivers. It also wasn’t obvious in my text that a D-Fly unit was required for ANT connectivity as well as Bluetooth connectivity.

By the way, on a Di2 mountain bike, all you need for connectivity to both cycling computers and smartphones is a Bluetooth-enabled digital display installed (along with updated firmware); you don’t need a separate D-Fly transceiver.
― Lennard