Ask a Mechanic | Converting 3×9 to 2×10

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Question: Loved the “Ask a Mechanic” article on the 2×10 XTR Budget Build. I have a question regarding my Cannondale Hollowgram SL cranks, setup for 3×9 spd. What are my options when changing over to 2×10 setup as described in the article post?  From: Derek

Answer: The world is your oyster Derek, as options abound for you. The best part of your situation is that you do not have to get a new 10speed shifter, rear derailleur, and cassette if you are on a tight budget. You can assemble and ride a 2×9 setup quite as I did for many years before switching over to 1×9 a year ago.

The rub is that most chainrings that are suitable for a 2x setup are made for a 10-speed chain. This is OK because 10-speed chains will work on 9-speed cassettes. 10-speed chains shift slightly slower moving up a 9-speed cassette but the difference is negligible to the senses of most riders, mine included.

Race Face Turbine 2x10 Chainring Set Black 26/38T

The rings of the Race Face Turbine chainring set are light, stiff and dependable.

Therefore, option number one is to get new chainrings for your crank, a new chain, and a 2×10 front derailleur (yes, they work with 9-speed triple front shifters they just need to be setup properly and no, you won’t have an extra click at the shifter if it’s done right). I recommend the XTR front derailleur as outlined in the article. For a chain I would choose the XTR M980 HG-X chain because in my experience Shimano chains pedal and shift smoother than anything out there. This is partly due to their new asymmetrical chain design that is engineered primarily to improve front shifting. Plus the XTR chains last a little bit longer than their lower-end counterparts.

With respect to chainrings, the most common 2x gearing setup is a 26t x 38t combo, which are available from Blackspire for your 104/64mm bcd (bolt circle diameter). While the shifting of the Blackspire rings is not on par with those of the big names, they are a decent option for a 104/64mm bcd. However, you could do a more climbing friendly 24t x 36t and get chainrings from every major player that would work with your current spider. Just keep in mind that you will probably need shorter “single speed” chainring bolts or chainring bolt spacers since you don’t have the extra ring to take up that space on the bolt anymore.

Option number two is to switch the replaceable spider on your Cannondale Hollowgram cranks to a 120/80mm bcd. This will allow you to go with some higher-end offerings for 26t x 38t and 28t x 40t chainring combos like these outstanding rings from Race Face. I have run the older Race Face RaceRings for nearly a decade and they always shifted with aplomb so I have no doubt these will too.

As far as selecting a cassette, rear derailleur, and shifter setup; should you go all the way with your 2×10 conversion, just follow my recommendations from the previous post. If you can swing it though, it is hard to beat a full XTR setup.

May your 2×10 conversion impart you with two times the fun on your next outing Derek.

Daniel Slusser is a professional bicycle mechanic with over ten years of experience. He holds a bachelor’s degree in business administration from HSU and a master’s degree in history from Cal Poly University. When he is not riding, wrenching, or writing he enjoys spending time with his wife and two children.