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Technical FAQ: Retrofitting a fork for QR15

  • By Lennard Zinn
  • Published Aug. 18, 2009
  • Updated Nov. 6, 2009 at 8:27 PM EST

Originally published August 18, 2009

Question: I recently purchased a new XC race bike equipped with a 100 mm Rock Shox SID Team fork. Because the improved handling seems to be worth a small weight penalty, I’d like to set my bike up with either a QR15 or a Maxle Lite front axle; however, I don’t want to buy a new fork just yet.

Can I retrofit my SID to accommodate a through-axle by replacing the lower legs with the lower legs from a Reba? If so, do you have any idea what kind of weight penalty would I be looking at (for the fork alone)?-Eric

Answer from RockShox: The short answer is no, this conversion cannot be done.

Here’s the longer explanation why – While the forks have the same 32mm upper tube diameter, the geometry and design of each chassis is quite different. The SID upper tube is significantly shorter than the Reba upper tube. Bushing placement within the lower leg is determined by the length of the upper tube. Installation of the Reba lower leg on a SID crown/steerer/upper assembly would not provide the correct bushing overlap.

At bottom out, the upper tube is also designed to contact a bottom out bumper in the bottom of the lower leg. This wouldn’t happen if the lowers were switched. Additionally, while both forks share a similar offset of 39mm, each achieves the final offset in a different manner.

The SID chassis has most of its offset in the dropout, while the Reba chassis has more offset in the crown. Installation of the Reba lower leg on a SID would result in a fork that had less than our standard 39mm of offset, compromising steering and handling.

-Sander Rigney, 
RockShox R&D

FILED UNDER: Bikes and Tech / Technical FAQ TAGS: / / / / / /

Lennard Zinn

Lennard Zinn

Our longtime technical writer joined VeloNews in 1987. He is also a framebuilder, a former U.S. National Team rider, and author of many bicycle books, including Zinn and the Art of Mountain Bike Maintenance and Zinn and the Art of Road Bike Maintenance, 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 degree in physics from Colorado College. Readers can send brief technical questions to Ask LZ.

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