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COST PER GEAR
Building a hardtail from scratch and need to pick a drivetrain. I have not seen any comparisons that show cost versus the number of gears. Can you help? Also, why do bike companies mix drivetrain components?
--Jeff, who saves his pennies
Mountain Bike Action:
You should run a 2x10 drivetrain if your hardtail will use 26-inch wheels and either a 3x10 or 2x10 drivetrain if you are going for 29-inch wheels. Cost per gear isn’t really a factor. Both Shimano and SRAM offer their drivetrains at a number of price levels, so there should be one to fit your budget.
Bike companies mix drivetrain components to save money so the bike they are offering hits an attractive retail price, or they do it to address compatibility issues with their frame designs. As a rule, we do not like mixing drivetrain components. The companies who make drivetrains go to great lengths to engineer their components to work together as an ensemble, and they certainly don’t share this information with each other.
MORE QUESTIONS ABOUT FEWER GEARS
Would like to switch to a 2x9 drivetrain. I want to go with SRAM and currently run a 3x10 with a 12-36 cassette and a 44/33/22 crank. I rarely face long climbs, but I do face short, steep climbs. I ride a carbon fiber, dual-suspension cross-country bike. What chainring combo from SRAM would you recommend?
--Dustin, who wants more than two front teeth
Mountain Bike Action
: Right now SRAM offers 39/26, 42/28, 36/22 and 38/24 chainring options for their X7 cranks. You can physically mix and match these chainrings (the mounting holes line up), but they won’t work as well as SRAM’s prescribed combinations because the rings have ramps and the teeth are shaped to help the chain move up and down. So if you mix, say, the 39-tooth big ring with the 28-tooth smaller ring, those ramps won’t line up properly. And, unless you totally luck out, shifting performance goes out the window.
With 26-inch wheels and your terrain, the 39/26 should be pretty good. The smaller chainrings are aimed at 29er guys. We think you are going to like the 2x9. We use it on our steep climbs and find we often clear stuff that we get hung up on in smaller gears.
POOR MAN'S 2X10
I would like run a 2x9 drivetrain described in your article ("Poor Man's 2x10" MBA August 2010) on my Pivot Mach 4 with an XTR press fit bottom bracket. I'm getting conflicting advice. I heard just throw the crankset in but I also heard I would have to replace the bottom bracket with an FSA Mega Exo and and some kind of adapter. How did you guys do it? -Rick M
Mountain Bike Action:
We explained in the "Poor Man" article to "Use only the FSA bottom bracket because it is engineered for the Afterburner 386 crank set, and this bottom bracket needs to be matched exactly to your bike." Some riders have tried to use a FSA bottom bracket with Shimano cranksets or visa-versa and while this looks like a fit, it puts too much pressure on the bearings and you will have problems. Shimano spindles are not true 24-millimeter diameter. We've heard riders bagging on FSA bottom brackets for not being durable when they mix and match components. That's just not fair. You just can't swap bottom brackets between these brands.
Okay, let's get the Afterburner on your Mach 4. This is going to sound a little complicated, but we've supplied a link to Park Tools that should help you.
Go to your friendly local bike shop and order the following:
FSA part number: 230-6022. It is a BB92 Steel Bearing BB Kit for the FSA Alloy MegaExo crank, BB-ALM92
This kit allows a standard FSA MegaExo threaded BB type crankset to fit into the FSA BB92 PFBB on Pivot frames. It requires a headset press to put it in. To remove the old Shimano plastic bearing cup, use Park Tool number BBT-90.3.
The Park Tool website has great step-by-step instructions on how to install the bottom bracket. Click here
to check it out.
We have added a lot of miles to our 2x9 project bike featured in the August issue and we are still loving it. You can order the August 2010 issue that includes the FSA Afterburner 386 crank installation and ride review by calling (800) 767-0345.