SRAM Precision – Cassette, Lockring and Chainring Issues

by Sabinna on July 17, 2010

I have been using SRAM groupsets–mainly Rival and Force with the occasional Red–for some time now, both on the bikes I assemble for myself and those assembled for dealers, local and international. In this post I will briefly explore some issues that I have noticed, one only recently. It is part of my forming an overall opinion on SRAM components in comparison to Shimano both of which I have used in equal proportions in the past, although this year I have used many more Shimano groupsets compared with last year.

Lockring Problem

The first concerns a Rival cassette which my mechanic was assembling onto an Easton wheelset. With this particular assembly when exceeding a torque of 25 nM, wheel rotation begins to be retarded. When the full torque of 40 nM is applied, the wheel cannot spin freely at all. Removing the cassette and just mounting the lockring, it was soon clear that this was the culprit. One solution to this is to place a spacer (1.67mm width) on the far inside as is standard with most Mavic wheelsets (excluding Record 11sp–you don’t need a spacer for precise  shifting). But, of course, this will not do.

SRAM cassette lockrings

Two lockrings that are not quite the same.

SRAM lockrings, SRAM lock rings

The standard lockring that we usually use has a depth of 7.4mm, seen here on the right. The lockring that SRAM provided with this more recent production of cassettes measure 8.5mm, seen on the left.  It is this 1.1mm of extra length that puts excessive pressure on the hub, enough to prevent free rotation.

Pedaling Backwards

The second issue concerns a peculiar riding practice that some riders engage in. In Singapore and Taiwan at least. I’m talking about rotating the crank backwards when freewheeling. It’s an issue that gets coverage in Bike Forums and Cycling Forums. About the best advice is “don’t pedal backwards”. Absolutely. But this is to jump ahead.

Fortunately not many cyclists do this and only three or four end users have reported this problem. It occurs when using the extreme gear (!! hardly recommended) – the chain is on the (standard crank) big chainring and the largest sprocket, usually a 27T. It is was also reported as occurring on the smallest (11/12T) sprocket.

Rotating backwards in either of these ratios causes the chain to derail to the outside of the large chainring. It takes from one to three rotations to produce this effect. Once we learned of the issue, we investigated on all bikes subsequently assembled. Most drivetrains lined up perfectly. Still there were a few that although lining up perfectly and shifting flawlessly, did produce the effect that customers were complaining about.

Our investigations found that substituting the SRAM-supplied chain with a YBN 10 speed chain or a Shimano 105 or above 10 speed chain ended the problem in all but one or two instances.

Although my SRAM supplier insisted this was a faulty frame issue, following basic checks on frame alignment, we found this to be baseless.

Red Compact Crank

Last week I assembled a bike for myself with a Red groupset, compact 50T/34T, 12-27T cassette. I found that operating the crank normally on 34T/12T ratio resulted in the chain slightly rubbing the inside edge of the 50T large chainring. It did not interfere with shifting, but indicated imprecision.

Measuring the chain with digital calipers revealed a width of 6.15mm. I acknowledge that these are actually not accurate enough to perfectly measure such precise tolerances. But it does reveal a discrepancy weighted towards the upper limit of acceptable tolerance.

Replacing SRAM’s chain with Shimano Dura Ace 10 speed chain, measuring 5.8mm, fixed the issue. It is something I have noticed in some of the Red Gruppos that I’ve assembled in the past, but as it did not interfere with shifting, I did not pursue it.

I’d not call it a “problem”, although given enough time I would expect that there would be end-user complaints about this. Legitimate or not, that’s how a select group of consumers feel about the technology they spend their money on. And, I can understand that point of view. When you outlay the cash for top-tier products it’s not unreasonable to expect perfection. Whether or not its realistic or practical to expect this is another question.

Conclusions

I have been very happy with SRAM groupset performances (another slight issue is the tendency for shifter hoods to tear more easily than Shimano), and still am. I feel, however, that their precision is not to the standard of the industry leader. And I acknowledge the point made by JM in a recent post, an “open letter” to Campagnolo (I highly recommend a read of this), that SRAM have come a long way recently and make great products. In this post he actually berates Campagnolo’s poor approach to marketing and so commending SRAM’s. Whereas there can be little to berate Campagnolo for on the technical side, there are some questions that SRAM may need to address to  re-balance their technical excellence/marketing mix.

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