This article originally appeared on Velo News
Have a question for Lennard? Please email us veloqna@comcast.net to be included in Technical FAQ.
Dear Lennard, I’d like to follow-up on this discussion that you so graciously published on the website. So, my follow-up questions are:
Besides the larger rollers of the AXS chain, is the gear/chain pitch different?
Why are the rollers larger? Is it to get more “grip” on the 10-tooth cog?
Ultimately, what matters to me is this (related to question 1): Is the roll-out/gear inches of a 12-speed SRAM the same as a Shimano 12-speed in, say, a 50-11 gear combination?
Dear Nigel, No, the chain pitch is the same.
Here's the skinny on the Flattop chain roller diameter from SRAM's road PR technical communications specialist, Brook Fowler:
"Our road drivetrain squeezes 12 cogs in slightly less space than our MTB drivetrain; we found that space by thinning the plates on the Flattop chain slightly while almost maintaining inner width dimensions (which helps maintain cog thickness and contact stresses on the teeth). The takeaway is the Flattop chain is narrower on the outer dimension and pretty much the same on the inner dimension -- this is achieved with thinner plates that were made slightly taller to maintain cross-section area. The taller link dimension is what actually drives the larger roller diameter of the Flattop chain."
Yes, rollout is the same.
Also read: Technical FAQ: Steel wires in tires, thru-axles, 10/11-speed upgrade, cleat fore-aft
Long time reader and learner from Kansas but who is eager to tackle some of Colorado’s climbs. As such, I’m looking for every opportunity to lower my gearing. I currently have Sram Red eTap 11-speed with the short cage rear derailleur (28T max cassette).
In addition to downsizing my chainrings to a 50/34, is it possible to swap my rear derailleur for the newer Force or Rival AXS eTap with 33T max? Will my older 11-speed shifters communicate with the new stuff?
Dear Joey, Again, SRAM's road PR technical communications specialist, Brook Fowler has been kind enough to answer this question as well, saying: "The 11-speed eTap shifters will not work with the 12-speed AXS derailleurs. Additionally, the first generation of RED eTap front and rear derailleurs are mechanically designed for 11-speed gearing and are not compatible with 12-speed chains, cassettes, and cranksets. Mixing and matching 11-speed and 12-speed drivetrain components (derailleurs, cassettes, chains, chainrings) are not mechanically compatible.
However, some of the 12-speed AXS shifters are backwards compatible with 11-speed eTap derailleurs. SRAM RED and Force eTap AXS shift levers or the eTap AXS BlipBox with firmware version 2.29.4 or later can be paired with RED eTap 11-speed front and rear derailleurs using the eTap pairing process. Rival eTap AXS shift-brake levers are not compatible with 11-speed eTap derailleurs due to differences in their electronic hardware and do not support this firmware feature."
If your foray westward into our Colorado mountains proves too much with a 34 X 28 low gear, then you might consider using a Road Link to get more gear capacity. You will need a longer chain, of course, along with the Road Link and the larger cassette.
Dear Lennard, I have a follow up question on the letter about thin steel wires in tires. I've had many flats caused by these also. My question is how can these tiny thin wires be strong and stiff enough to penetrate a tire and a tube to cause a flat? If somehow they were sticking straight up in the road it seems they would just be crushed. It seems more likely they would be lying flat which would make it nearly impossible to then penetrate the tire. Any thoughts?
Well, that's a good question. My guess is that you do regularly ride over thousands of these wires that are lying flat, and that it is a rare one that is somehow oriented in such a way that it pokes into one of your tires. It would be interesting to, with a magnet, go through the contents of what a street sweeper pulls up off of the road. I would be surprised if the magnet didn't get immediately furry with countless little pieces of steel wire, meaning that there are so many that you constantly ride over that even a low-probability occurrence like one standing up can still occur frequently due to the sheer number of them.
If that were to turn out to be true, then the question is, what would the conditions have to be for the occasional one to give you a flat? Perhaps every now and then one drops into a space alongside one of the gravel chunks in the asphalt and ends up sticking straight up. Where the car tires are rolling, I imagine you are correct that vertical wires would be crushed (or picked up by car tires). On the shoulders, though, they would tend to sit there for awhile. Around here, when we get a torrential downpour that creates rivers of sediment depositing sand and gravel on the road, the sand and gravel ridges quickly disappear from the car-tire paths, but they stay on the shoulders perhaps indefinitely until a street sweeper remove them. So those wires could sit on road shoulders a long time, un-crushed, awaiting your bike tires.
When I used to build steel, fillet-brazed frames, I would rough out the shape of the brass fillets with a flame-shaped carbide burr bit. I also used to shape the ends of the chainstays and seatstays where I had brazed them to the dropouts using the same tools. This produced millions of tiny, sharp slivers of brass and steel on the floor that sweeping was not 100% effective at removing. Even though the slivers were lying flat, you could not walk barefoot in the shop without getting some sticking straight up into your feet. And the floor was very smooth concrete, as opposed to the rough surface of an asphalt or concrete road.
I suppose the movement of the surface of the skin as it pushed off from the floor to take the next step might have stood some of the splinters up to the point that they stick into the foot. If that's the case, perhaps the flexing of the rubber tread as it rolls along could also pull the occasional wire into a vertical position, letting it stay standing up on the tire as that section of rubber leaves the road and goes around and back to contacting the road again, pushing that wire straight in each time it hits bottom. Interesting to think about; all just conjecture.
Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder and purveyor of non-custom huge bikes, a former U.S. national team rider, co-author of “The Haywire Heart,” and author of many bicycle books including “Zinn and the Art of Road Bike Maintenance,” “DVD, 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 in physics from Colorado College.
For exclusive access to all of our fitness, gear, adventure, and travel stories, plus discounts on trips, events, and gear, sign up for Outside+ today.
This supersize set will give you a sun-kissed look without the UV damage.
Get in on the end-of-summer bounty with amazing deals on top brands — from just $16!
Have XL pores on your nose? This dermatologist-approved winner scoops out all that oil and dirt.
The model and actress explains her comfortable approach to fashion.
Save 55% on this popular lightweight bedding while you can.
Amazon's top-seller is quite the smooth operator: 'The wheels spin and move like butter on a hot pan!'
Coach, Dyson, Skechers and more: Save over 50% on items you'll love busting out this fall and beyond.
Have yourself a squeaky clean autumn with epic deals like a Dyson upright for nearly 40% off.
The Mophie Go Air Jump Starter is a lifesaver on the road and at home.
Forget changing out batteries all the time — these cameras are fueled by the sun.
Start your holiday shopping early and snap up epic gaming deals all September long (while supplies last).
The secret ingredient is goat milk — and it comes directly from a herd raised at the brand’s headquarters in upstate New York.
Give your back a break with Sleep Number, Casper, Bear and more.
The shopping event we waited for all summer is still going (but not for long)! Tons of appliances are massively discounted!
Score big on TVs, headphones, laptops, video games, tablets and so much more this holiday weekend.
Some products are open-box, some are pre-owned and all are guaranteed. What a way to save!
Soft Touch exfoliating tootsie treatments were designed by a skincare pro: 'Better than Baby Foot.'
Side sleeper? Back sleeper? No sweat — these top-rated bedfellows work in every position.
While the Big Mac could never be replaced, McDonald's locations in Florida are testing out a new twist on an old classic.
Gigi Hadid is opening up about motherhood. In a preview from Sunday, Sept. 11th’s episode of Sunday Today with Willie Geist, the model — who just launched her new fashion line Guest in Residence — gave an update on life with 2-year-old daughter Khai. The star shares her only child with her former partner, One Direction alum Zayn Malik.