Garmin Arm Mk II Improvements

Garmin Arm Mk II Improvements

Garmin Arm Mk II Improvements

Broken quarter-turn inserts and disconnected Varia lights are a challenge for all Garmin Varia mounting options. These inserts are designed to be sacrificial, but can also weaken and break during normal use as well. At Bup Labs, we have grappled with this problem for years. Our mounts secure the Varia and prevent twist out, but they are still subjected to heavy loading depending on the bike and riding conditions. Bup's latest revolutionary design secures the Varia, prevents twist out, and removes the load from the insert. No other mount on the market does this.

The Problem With Garmin Varia Mounting

The Varia RTL 510, 515, and the RVR315, all suffer from the same problem.  They all rely on the small, plastic quarter-turn insert to absorb all torsional loads on the connection during a ride.
Normal Varia mounting solution
Insert cup only with Varia
The quarter-turn insert was designed to handle horizontal loads, not vertical loads.  When the Varia is under load, the weight of the battery at the bottom causes it to torque on the insert which can lead to an insert failure. There is only 1 to 1.5 mm of plastic to support the entire load from the Varia.
Insert loading
Quarter turn insert cutaway
This load translates directly across the centerline of the insert, constantly pulling on the top ridge and torqueing the bottom of the center support at the screw holes.
Traditional quarter turn insert stress point

Bup's Solution

The first change involved moving to traditional OEM Garmin quarter-turn inserts. These inserts are thicker and harder to flex but unfortunately much more expensive to manufacture. This is why 99% of the 3rd party computer and Varia mounts on the market use traditional inserts secured with two flat head screws.  Below you can see the difference between the OEM insert (left) and the typical 3rd party insert (right):
New vs old quarter turn inserts
The second change was adding a tab at the bottom of the arm to brace the Varia and limit the torque on the quarter-turn insert.  This has a greater affect on the RTL 510 and 515 due to their length.
Mk II vs Mk I mount arms
The Garmin Mk II arms accommodate the RTL500, RTL510, RTL515 and RVR315 Varia models.  Please note that the rubber ring will not work with the original Review Radar light.
Mk II with RTL 510-515
Mk II with RVR 315

Upgrades and Support


At Bup Labs, we are constantly evolving our designs to make cycling safer and provide the best mounting solutions. This wouldn't be possible without the invaluable feedback from our customers and testers who are cyclists of all levels.

If you already have a Mk I Garmin arm, it is designed to help mitigate the load on the insert and hold the Varia without issue.  However, due to feedback from various users we identified that certain lots of specific quarter-turn inserts could possibly fail.  We created a program to replace the affected inserts for free. There are two options for affected customers:

  1. Get a free replacement quarter-turn insert kit that replaces the problem insert
  2. Upgrade to the Mk II arm at a heavily discounted price.

For details see the KB-00008 - Free Garmin Insert Replacement article.

If your Mk I arm does not meet the criteria in KB-00008, there is no need to upgrade to the Mk II for fear of failure.  We have thousands of units in the field that are working without issue.  Only a narrow band of customers that are affected by the problem above should contact us for a replacement or upgrade.

Last Updated Feb, 2023

Older post Newer post