Gear

Technical FAQ: Fixing front-end shimmy, and SRAM battery woes

Lennard offers advice for solving fork vibrations, and troubleshooting SRAM battery drain.

Have technical questions? Send me an email to veloqna@comcast.net.

Dear Lennard,
I’m pretty sure this issue has come up more than enough, but I wanted to share my experience with you. My Calfee started shimmying badly, but only occasionally. Rich Sullivan said he was sure it was that the tips of forks were starting to flex and that a new one would solve the issue — and it sure seems to have done the trick. I’ve pushed my bike in the corners and on the straights downhill, hitting the little road imperfections that used to set the shimmy off, and I can’t get it to start the shimmying anymore. So, while all manner of frame design and physics properties may come into play, maybe a person’s carbon fiber forks are simply old (mine were ten years old, and had 40,000+ miles on them).
— Andrew

Dear Andrew,
I always like giving readers alternative methods for dealing with front end shimmy — since it can be such a scary and pervasive problem — and any solution that solves the problem is a good one. I checked with Rich Sullivan and Craig Calfee at Calfee Design, and they gave me a further explanation of how this might have come about and why a new fork solved it.

Calfee says:
“Carbon fiber doesn’t really age and get more flexible. Metals fatigue and start cracking and that can cause loss of stiffness. I would really like to inspect his fork. Probably either asymmetry or starting to crack at the crown. Both are known issues with older Alpha Q forks, and some others. Also, loose dropouts can be another cause.”
Craig Calfee, founder, Calfee Design, Inc.

And Sullivan says:
“Many fork manufacturers nowadays recommend replacing forks every 5 years. Whether or not we would agree with this protocol is beside the point. However, when you think about how many cycles of bumps, vibrations, braking and steering forces, and crashes that a fork undergoes, it makes sense that forks begin to flex and fatigue; especially when they start to reach the two-decade mark or so many thousands of miles. I occasionally receive calls from clients with older frames that start to complain of this shimmy in the front end. A new fork has always corrected the issue. Another solution we provide to our clients with older Calfee frames is to upgrade the head tube from 1″ to 1 1/8″, plus the purchase of a new fork. Customers are beyond stoked!”
Rich Sullivan, sales and marketing manager, Calfee Design, Inc.

While fatigue is not generally an issue with carbon fiber composites, cracking, delamination, impact damage, and de-bonding of glued-together sections can be. Replacing a fork that has been crashed is a no-brainer. So is replacing one that has been on the bike for many years, especially if now the bike has developed a shimmy it never had before.
― Lennard

SRAM’s eTap rear derailleur has a battery mounted to the rear. The battery is interchangeable with the front derailleur battery. Photo: Caley Fretz | VeloNews

Dear Lennard,
The battery in my rear derailleur will drain completely if I leave it in overnight (the front one is fine). I’ve swapped the batteries around, but I get the same result.

The SRAM 11-speed eTap groupset isn’t even a year old.
— Jim

Dear Jim,
This is SRAM’s response:

“If the battery is draining overnight, there are a few things he can do. Remove the battery overnight to save battery power (this is temporary: until there is a solution in place). Make sure the bike is not moving in overnight storage (we had a customer who had a bike hanging in a shed, the bike moved on a hook during strong breezes in the night. This is highly uncommon: he was on the Scottish seashore where the wind was strong enough to bounce his bike around at all hours through his drafty shed, keeping the accelerometer going and never letting the system sleep) If the bike is stationary overnight and the battery is still draining, please have him return to his original place of purchase for a warranty evaluation.”
Brooklyn Fowler, SRAM road technical marketing coordinator

― Lennard


Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder (www.zinncycles.com) and purveyor of non-custom huge bikes (bikeclydesdale.com), 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