Mountain Gear

Tech FAQ: Converting 3X to 2X

Can you convert your 3X9 drivetrain to a 2X9? LZ has the answer

Dear Lennard,
With converting a 2008 3×9 XTR 970 system to a 2×9, I’m thinking of going to the XTR M985 double crank, which is designed for a 10-speed set-up.  Will I have any issues running a 10-speed chain with the 9-speed XTR cassette and rear derailleur?

Should I be thinking of other crank options in going to a double?
-Thomas

Dear Thomas,
TechWidgetI have not tried that particular combination. I have however, tried all manner of combinations of 10-speed and 9-speed drivetrain components. From this experience, I would be willing to bet that you will have no problem with either of the following options:

1. Running a 9-speed chain on the new 10-speed double crank: With road doubles and triples of many different brands, I have often used a 9-speed chain on 10-speed cranks and had very good shifting and no thrown or jammed chains or any other unpleasant occurrences. And you of course know, since you have been using a 9-speed chain on your cogs and rear derailleur and with your shifters, that you will have no problems with a 9-speed chain in the rear, either.

2. Running a 10-speed chain on your 9-speed cogs and rear derailleur (as you asked): I have used 10-speed chains with 9-speed road and mountain rear derailleurs quite often – and I still do it currently to achieve wide gear ranges on road bikes. Just a couple of weeks ago, for a customer who wanted an extremely wide gear range, we set up one of our custom coupled titanium road frames with a 64/104mm BCD mountain crank with 20-36-48 9-speed mountain chainrings (the 20T was a titanium ActionTec ring), Ultegra STI 10-speed triple road levers and triple front derailleur, an XTR 9-speed rear derailleur, an 11-36 SRAM XX cogset, and a SRAM 10-speed chain. It’s working great, and the customer has already ridden in Europe and the Caribbean with it and is very happy with the shifting. It was sensitive to the chain selection, however. The shifting was sluggish with a Wippermann 10-speed chain, but it was just fine, front and rear, with the SRAM chain.
-Lennard

Readers can send brief technical questions directly to Lennard Zinn.

Technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of numerous books on bikes and bike maintenance including the pair of successful maintenance guides “Zinn and the Art of Mountain Bike Maintenance” – now available also on DVD, 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.”

Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn.

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