Rear shift performance of the new 2012 Red kit feels very similar to the 2011 Red group. SRAM kept their 1:1 cable pull-to-derailleur movement ratio. It still has that definite click and feeling of solid resistance, but the whirring, clanking and reverberating of last year’s Red kit is gone.
2011 Red shifts very precisely, but makes a lot of noise due in part to the hollow cassette and derailleur pulley tooth design. The hollow cassette design is gone, although most of the cogs are still constructed in a single unit. All cogs but the largest are machined from a single block of steel and connected to each other. The biggest ring is aluminum. Holes are drilled between the larger cogs to save weight and elastic rings are slotted between the cogs to help quietly guide the chain on to the cogs.
The idea behind these elastomers SRAM has dubbed “StealthRing” is to provide a soft surface to catch the chain as it is guided on to the lower segment of the cassette under minimal tension. A deeper trough is machined from the rear half of each grove and the elastomer protrudes slightly into this gap. As the chain links move from to the top of the cassette and gradually accept more of the load, the links are pulled off the elastomer and into contact with the metal tooth only. Durability of these rubber parts is the obvious question but SRAM’s initial ride and lab testing shows that the elastomers last a very long time, although not quite as long as a cassette in some cases. Should they degrade or break, SRAM offers replacement rings. The system should continue to work if one breaks.
The other change intended to quiet the rear part of the component group was made to the derailleur pulleys. The old pulleys have blunted teeth that make a whirring sound when the chain rolls onto them. The side of each tooth that first connects with the chain has been narrowed to smooth that transition.
Although we can’t say which change is responsible for the improvement, the rear of the bike is much, much quieter. Riding in a pack of bikes built with 2011 Red is cacophonous, but the group of bikes on our test ride was whisper quiet.
The standard derailleur can accommodate a cassette with a climbing gear up to 28 teeth and a version capable of fitting SRAM’s cassette with a 32-tooth cog will come later in the year.