Hack: Drop 6 Grams From New SRAM Red Cassette – And Why You Shouldn’t Do This
Here at Bikerumor, we like to make lemonade from lemons. And, in the process of testing things, we have more than our fair share of opportunities to quench our thirst.
Above is the main cluster of a new SRAM Red cassette broken down to it’s three components. Hopefully, you’ll never see your own cassette in such a state. But, as, um, “luck” would have it, certain things were stuck on a freehub body and before long hammers and flat head screwdrivers got involved. This is the result.
Here’s where we started squeezing lemons…
Before we get started, let me say this: What we did here is not recommended by SRAM and not something we recommend you do. Take it for what it’s worth, the real value here is knowing that should your own Red cassette explode, you can put it back together. It’s not a goner. That’s very comforting considering the street price for one of these is about $340!
The main cluster consists of a back plate that doubles as the largest cog, a one-piece machined cog cluster for the 2nd through 9th gears, and the inner sleeve. The back plate and cog cluster are pressed together with high pressure, but there’s no bonding agent. The sleeve rests between them and is captured by ridges to it won’t move out of center. It does slide laterally slightly, and we’ll explain why in a sec.
The cog cluster has evenly spaced tabs that slot into holes on the backplate (click image to see it larger). One hole/tab combo is larger, which keeps gears lined up properly. To press them together, I used an adjustable wrench and carefully yet strongly pressed the pieces back together, working around the perimeter evenly. However, I intentionally left the inner sleeve out…and saved 6 grams:
Then I put it back on the bike and went for a 27 mile ride. And it worked flawlessly. Shifting was as crisp and precise as usual, and there was no rattling around. The interface between the smallest cog and the cluster ensures that it sits in center line with the freehub body:
Note the little ridge on the inside edge of the small cog. The cluster rests on that for support. Once the lock ring is on and tight, the cassette has no play. All this begs the question: Is the sleeve like an appendix, there but unnecessary?
According to SRAM, no. It is in fact a functional and important part of the cassette. Here’s what Frank Schmidt, one of SRAM’s drivetrain engineers, had to say:
We need the ‘tube’ as we call it, because on the broken-up structure of the cassette there is no other good spot for a decent logo.
No, seriously it is an important part of the structural concept. Driver bodies of the various hub makers are not very consistent in regard to length and lockring thread depth. So tightening the lockring without the tube would uncontrollably compress the cassette cluster and aluminum cog until the lockring bottoms out. This would result in more or less dishing of the aluminum cog and also all steel cogs messing up the total stack height and also the distance between each of the cogs. Also it would create undesired axial stresses in the structure. And it would be likely that the lockring gets loose in use. With the tube the compression is 100% controlled and independent of hub variation.
So yes, it is necessary.
The cluster and the biggest cog are pressed together. This is being done with high pressure and precise distance control. It is definitely not recommended to open that connection for cleaning (or to take the tube out to save 5gr). Reassembly without proper equipment will likely cause wrong distances, wrong orientation and/or damage to the cog. Also the connection will be much weaker after disassembly. The tube is just put inside before pressing on the cog. There is actually a small gap between the parts, when the cassette is not mounted. This will disappear to achieve a controlled compression under lockring force.
So, should you do this? Honestly, no, and definitely not if it means trying to disassemble a perfectly good Red cassette just to do so. That said, here we are with a long term test bike with this cassette, so we’ll put some miles on it and see what happens. We always hope for the best, of course, but at the very least, it’s nice to know you could reassemble this fine piece of machined metal if things go south the next time you’re wrestling it off a chewed up freehub body.