Technical FAQ: SRAM eTap battery fix, carbon bikes on trainers, wide pedaling angle, tire rolling resistance

Tech expert Lennard Zinn offers suggestions on how to fix shifters, if it's OK to ride a carbon bike on a trainer, and optimal tire setup.

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Dear Lennard,
All of a sudden, I have to change a coin battery in my SRAM eTap right shifter every two rides. Please let me know if there is a solution to this problem before I throw my eTap in a trash can. That’s too much.
— Miro

Dear Miro,
Yes, there is. It is quite easy, and you will be glad you did it. The same thing happened to me with my 12-speed eTap AXS road shifters, although it has never happened with my 11-speed eTap shifters that I have ridden for years.

The simple answer is this: download the eTap app to your phone and do the software update. That will fix it. Once you’re in there, you can customize your shifting the way you want it as well.

Here are the details. First, sync your AXS parts to the SRAM AXS app the tutorial also shows you how to vary the control settings for shift function.

To update the firmware, which you will do for each component in the system, you will need a WiFi or cellular connection. Do not close out of the app while the firmware is updating.

Once the parts are paired to the app, press the function button on the part to wake it. Select each individual part to see if there is a firmware version available for that part. It will look like:

SRAM AXS mobile app
SRAM AXS mobile app firmware update.

The firmware will confirm the successful update when it is completed. It is satisfyingly quick, the update instructions in the app are pretty clear, and setting up the shifting settings is nice. Mine is now set up to auto shift the front derailleur once I reach certain gear combinations, which I had grown to love on my Di2 gravel bike.
― Lennard

Dear Lennard,
In your experience, is using a carbon frame in a rear-wheel-off trainer harmful? What about one where the front fork is attached?
— Lee

Dear Lee,
As you can see in this post about using a carbon frame in a trainer, there is some cause for concern, especially where the trainer attaches to the frame or fork. If you can ascertain from your bike manufacturer that it is fine to do it, that’s the best-case scenario. The likelihood is that you can train indoors on your bike without creating significant damage.
― Lennard

Dear Lennard,
My physical challenge is the “unstraightness” of my right leg, which I am convinced has its origin in my hip (from birth). It causes my right foot to angle out to nearly 45 degrees when fully extended. I’ve been looking for an exceptionally wide platform peddle to enable me to more easily keep my right foot and leg at full power on the go. So, I’m looking for a pedal of about 130mm in width. (So far without success.) Would you have any suggestions?
— Jim

Dear Jim,
I don’t know of platform pedals that large. Do you want a platform rather than a clip-in pedal just to get the width? How about using Speedplay pedals with a super long spindle? For instance, the Speedplay Zero pedal spindle can be as long as 65mm of extension, which is a half-inch more than standard. While the outside of the pedal won’t be near the 130mm you’re looking for, your foot will be far beyond it; the pedal body sits a bit inboard of the middle of the forefoot, and the pedal and cleat allow a wide range of rotation of the heel to the inside. Even though the pedal is small, the interface with the foot is large relative to other clip-in pedals, and the long spindle would allow you to angle your foot out without clipping your ankle.

If that’s not enough length for your heel to clear, you can get a pedal extender that adds another 20mm of length to the spindle.
― Lennard

Dear Lennard,
Recently I finally, after 12 years, I was able to upgrade my road bike. I really liked the idea of getting a bike that could take a larger tire for comfort and durability. I test rode a bunch of bikes and settled on a bike that could take up to a 32c tire. My wheels are tubeless-ready, so I am ready to take the leap if the technology is worth it.

Riding to work this morning I was wondered if you or VeloNews ever did a test for the “optimal” tire size for comfort and speed, (tubed or tubeless), as well as PSI recommendations? I understand that everyone’s perception of “comfort” is subjective. I’m not talking a mix of gravel, dirt, or asphalt surfaces. Just good old fashion cracked up and smooth asphalt roads.
— Chad

Dear Chad,
There is a lot here in this podcast about tire performance on that.

This is a test we did on road tires eight years ago, from a time before road bikes were moving to tires wider than 27C.

This is the first of two gravel road tire tests we did two years ago with electronic timing. It’s not cracked or smooth asphalt; it’s a hard, dirt road with minimal gravel and some washboards with different tire pressures on 700 X 35c tires.

I also did a second magazine article on this subject, using the same electronic timing and stretch of road with a range of tire widths as well as pressures. It would have been in the September 2018 issue of VeloNews or thereabouts. In it, we tested tires from 700 X 25c to 700 X 36c (whose actual widths measured from 27.2mm to 35.9mm wide) at 30, 40, 50, and 60psi.
― Lennard

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.

Follow @lennardzinn

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