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ASK RBA: ASK RC: COMPACT CRANK AND CASSETTE COMPATIBILITY
Richard Cunningham
August 31, 2009
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I am building up a Trek 1.2 and decided to go with SRAM Rival because of the weight and cost benefits. Since sometimes I still need to use my triples smallest chainring on certain climbs I thought it was a good idea to get a compact crank. I got a 50/34T Rival crankset. I thought all my issues were solved so I went out and got a Shimano Ultegra cassette and without even considering gearing, I got a 12 X 25. After reading a lot of "arguments" on bikeforums.net about people getting compact cranks and whether or not the cassette compliments their crank I have a few questions. As I understand from these conversations there are certain cassettes that could make the compact crank null and a complete waste. I am a strong rider and push very hard but I am no pro and my top speed on the flats is around 24 mph with the setup I have now. I climb a lot though, as San Diego has a few "hills".
Basically with the setup that I have now, did I lose a lot of my top end...so much so that I would actually notice it? Does my cassette compliment my crank for climbing? Will I have any issues with certain combinations such as big chainring and little chainring gear ratio overlap? Nobody can answer my questions on the forums, beside saying "put it on your bike and find out." Thank you for your time and patience in answering these questions.
– Jesse
Your choice of a 12 X 25 Shimano cassette will not kill your performance. SRAM designed its compact Rival, Force and Red ensembles to work with an 11-tooth cog. This is necessary to achieve top speeds that will match conventionally geared drivetrains which use 53 X 12 top gears. My favorite compact gearing is an 11 X 26 cassette because it offers a lower low and an equivalent high gear compared to a conventional setup. You will enjoy the versatility of a compact Rival crankset paired with a 12 X 25 cassette (especially when climbing), and you will easily be able to reach 24 miles an hour. We have a radar speed trap on my 45-mile training ride and my top speed through the trap is 43 miles an hour—and I have yet to approach my maximum RPM in the 11-tooth cog. Keep your cassette and concentrate on spinning a smooth 90 rpm cadence. When you wear out that cassette, then you will be able to make a more informed choice for your next gearing. I’ll bet you will stay with the 12 X 25. San Diego’s old 395 route and its adjoining canyons can test anyone’s legs. By the way; SRAM’s Rival group is a great performer—I know you’ll enjoy it.
Contact Richard Cunningham for questions or comments, or just to talk bikes at: askRC@roadbikeaction.com
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