Hack: Drop 6 Grams From New SRAM Red Cassette – And Why You Shouldn’t Do This

SRAM Red cassette hack and repair

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…

SRAM Red cassette hack and repair

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:

SRAM Red cassette hack and repair

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:

SRAM Red cassette hack and repair - or how to reassemble a SRAM Red cassette

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.

Comments

Topmounter - 12/07/12 - 11:18am

Does the XX cassette come apart in the same fashion? My 36t cog wears quicker than the rest and swapping in a fresh cog would save me some dough.

Hungry4Shht - 12/07/12 - 11:22am

What does SRAM do with all of the leftover metal after CNC’ing those tiny bits from a giant hunk of aluminum?

Does it become pART?

SRAM make, the world takes… does SRAM refuse get put back to use?

Steve - 12/07/12 - 11:23am

Does the cassette only touch the freehub body at the two outer edges? It seems like that wouldn’t be a good idea, so hopefully your long term test can shed some light on that.

g - 12/07/12 - 11:29am

wow! 6 grams! totally worth any risk of ruining your cassette. Good work gentlemen.

Nick - 12/07/12 - 11:40am

@Steve: Yes, the only places the cassette transfers power into the cassette body are via the back plate/cog and the smallest cog.

It’s not a problem, it’s not unlike any other cassette that’s made out of individual cogs with spacers in-between.

johnny - 12/07/12 - 12:00pm

Please put in a little more detail on these cassettes getting stuck on the freehub body!

I have had 2 XX cassettes get stuck on a Mavic body. Luckily, the the LBS and SRAM waranted the first, but now the replacement is stuck. The concept of these machined out cassettes is interesting but the interface is worthless. I am hoping that the interface of the XX1 is an improvement as I would like to switch to that group soon.

klarf - 12/07/12 - 12:01pm

You can remove the elastic like here:
http://veloptimal.com/forum/viewtopic.php?f=2&t=32427&p=762217&hilit=moots+compact#p761800

A other gain of 6g :)

Johnny Doe - 12/07/12 - 12:09pm

Next time y’all have a stuck cassette on an alloy freehub body, loosen the lockring enough that the small cog can wiggle just a hair, and use two opposing chain whips, one to turn the large cog counter clockwise to free it from the splines of the freehub body that it has dug into, the other pulling clockwise on the small cog to keep the freehub body from freewheeling. Like Colt 45, it works every time.

NoBodyMan - 12/07/12 - 12:25pm

@Hungry4Shht

Most machining captures the cut material and it is either sold for salvage or recast and used.

mudrock - 12/07/12 - 12:43pm

Not a good idea. removing the tube puts the cassette in compression between the small cog and alu large cog – not the strongest material. Sram did their homework; bikerumor did not.

Duder - 12/07/12 - 12:51pm

@Johnny: The XX1 cassette, while machined and pressed together in a similar fashion to the X-Dome cassette on Red and XX, attaches to the cassette in a totally different manner. It’s better to see it in person, but I’ll give it a shot:

The 42t aluminum cog has a “normal” splined interface similar to any shimano-compatible freehub that locks into the base of the new SRAM XD freehub body. The “tube” in the center of the cassette then rotates freely relative to the rest of the cassette and threads onto about 10mm of threads directly above those splines on the freehub. The rest of the freehub is smooth.

Steve - 12/07/12 - 12:55pm

@mudrock – Did you even read the article?

Barburuksi - 12/07/12 - 1:19pm

I think most people just look at the pictures and make comments off the cuff

Tyler (Editor) - 12/07/12 - 1:36pm

@Johnny Doe – Brilliant, thanks!

@Johnny – We put this on a freehub body that had already been pretty chewed up by a normal (in that case Shimano) cassette, which has grooves on every cog. It’s generally not an issue when you’re putting a Red cassette onto a fresh freehub body. We just got our parts in to mount up the XX1, so we’ll report back soon (new post) when we’ve had a few rides on it.

G.. - 12/07/12 - 3:23pm

“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.”

I think BR summed it up pretty well at the end of the article.

And honestly, 6 grams? C’mon folks, there must be more interesting things to do with one’s time rather than trying to save six grams….

g - 12/07/12 - 6:11pm

another? g imposter? this is getting out of hand guys

carl - 12/07/12 - 6:33pm

Of course, if you took the tube and drilled it out and then PUT IT BACK IN…. what? 2 or 3 grams? TRICK!

Dr. Strangebike - 12/07/12 - 6:57pm

you could probably lose a few grams by removing all the rubber bands from the cassette but that is a dumb idea as well

bin judgin' - 12/07/12 - 9:20pm

you could use the old SOLID red cassettes as good small flower transportation devices. don’t tell the cops!!

also drillium dude!! carl is on course!

Loyd flanders - 12/07/12 - 9:57pm

I can’t believe a discussion has been made about a total mass saving of 6 grams, that is like drinking 6mls from your bidon. Please, I read this article thinking you would get to a point that was a profound finding, not the case. SRAM spend a lot to engineer these parts I’ll opt to keep my 6 gram crush tube please. Another good article should be on getting a hair cut and nail trim to save a few grams!

MissedThePoint - 12/07/12 - 9:58pm

carl, yes, but don’t stop there. Drill your brake levers, your seat tube, your crank spindle, your stem, your fork steerer, your hub shells… gotta be at least 100 grams worth! TRICK!

Weight Watcher - 12/08/12 - 6:11am

@Hungry4Shht: I think the main body is made of steel ;-)
@Nick: You’re right, the interface for torque transmission is similar to that of single cog (or a cassette consisting of single cogs). But this single cog is made of ALUMINUM =.O

Here’s another idea to save weight: As the toothing in the middle of the freehub body isn’t needed, you can turn it down ;-)

g - 12/08/12 - 10:02am

Don’t stop there. Scrape the hideous Sunday Fred billboard paint of the frame and fork with a razor blade. That ought to save you at least the mass of nine fingernails.

Bananarama - 12/08/12 - 10:12am

Why was this article posted? Do you guys at BR seriously have nothing better to publish? “Hey, here’s something you can do, but don’t do it because it’s bad.” Sounds like G.I. José.

G.. - 12/08/12 - 4:44pm

Imposter? IMPOSTER! The hide of some people I say. I Sir, am an uppercase G followed by several periods, usually three, sometimes two.

I have been this uppercase G (followed by two or three periods) for many a year. It is you, who undoubtably has some questions to answer ;)

G..(.)

g - 12/08/12 - 10:42pm

fair enough, sorry ’bout that. -g

Steve - 12/10/12 - 7:39am

Street Price of $340? You can get these for $239 on the bay..

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