122 gram rear derailleur


Lightweight Carbon Rear Derailleur ($1,200 with a claimed weight of 120g)

I’ll admit that I’ve got weight issues, and an intervention from my friends and family is probably in order, but until someone freezes my credit card in a block of ice I’ll probably keep spending money to shave grams from my bike. Now before I go much further, I have to give credit where credit is due. I didn’t come up with the idea of tuning my rear derailleur, rather I read about it on the Weight Weenie web site in their forum. A fellow Weight Weenie and friend of mine, Nathan (aka “coloclimber”), made a post about how he took his SRAM Red rear derailleur down to 128 grams. What was most interesting to me about his post was that his rear derailleur was almost as light as the Lightweight (that’s a brand) super-sexy, but crazy expensive carbon rear derailleur (pictured above). The yet-to-hit-the-real-world (read “vaporware”) Lightweight derailleur costs $1,200 at Competitive Cyclist, and is claimed to weigh 120 grams. You can buy quite a nice frame for $1,200 so buying just a rear derailleur for that amount is beyond what even I’m willing to do. But spending $265 for a 128 gram rear derailleur, which is what “coloclimber” claimed could be done (with a little help from eBay, dark_albert, and Microsoft Cash Back) sounded quite sane to me. That being said, I’m a bit lazy and didn’t have the energy to actually track down dark_albert and buy the necessary parts.

My stock SRAM Red rear derailleur

My stock SRAM Red Rear Derailleur (145g)

Then one sunny autumn day I got a call from Nathan. It turned out that Nathan decided that his next project bike would be an Italian aero beauty rather than a fragile featherweight. Nathan was replacing his SRAM Red with Campy 11-speed and offered me the derailleur parts he used to tune his SRAM Red derailleur. In addition to the dark_albert pulleys and back plate, Nathan had purchased an aluminum cable adjuster that he never got around to installing. He handed me a Ziploc bag with an assortment of carbon and aluminum parts and I transferred some money into his PayPal account. Nathan not only gave me a good deal, but he made the whole thing easy. I didn’t have to order parts from Germany, and he gave me some good advice on how to install everything.

I started off by removing the pulleys and rear plate from my SRAM derailleur, and I replaced them with the carbon pulleys and the carbon plate. This took all of about 10 minutes and was quite simple. The carbon rear plate is significantly thinner than the stock one and because of this you can’t use the stock SRAM pulley bolt for the top pulley because it will bottom out in the derailleur. Nathan included a shorter bolt in the Ziploc bag and I assume that it came with the carbon plate when he purchased it. The bottom stock SRAM pulley bolt can be used, however, because it threads into carbon plate rather than into the derailleur, and the extra length just means that it protrudes a tad beyond the back plate. I suppose if you wanted you could file or grind that bolt down a millimeter or two and drop a fraction of a gram, but I was lazy and left it sticking out.

SRAM Red with new pulleys and carbon plate (126g)

SRAM Red with new pulleys and carbon plate (126g)

At this point I had done the same as what Nathan had done and my rear derailleur was down to 126 grams. That’s a few grams lighter than Nathan’s was, but I’m pretty sure that my stock SRAM Red rear derailleur was just a tad lighter than his to begin with — just lucky I guess. (I’m fairly confident in the accuracy of my scale.)

The final step was to replace the stock barrel adjuster with the significantly lighter one Nathan gave me. I think that the light barrel adjuster he gave me was designed to be used on the frame up at the braze-on cable housing stops near the top of the downtube, and was not intended to be used on a rear derailleur. But it was about the right size, and it included a spring to prevent it from creeping, so it looked like it would serve well as a replacement for the tanky stock one. Nathan said that when he purchased the barrel adjuster that they only came in pairs, so he bought a set of them. He kept one and gave the other to me. Removing the stock SRAM barrel adjuster was perhaps the hardest part of this project. There is a little circlip under the barrel adjustment assembly and unless you are one of Santa’s elves with tiny fingers, or have a better arsenal of tools than I, removing it without gouging the aluminum body of your derailleur isn’t easy. I ended up using a little screwdriver, and I did put a few small scratches in the underside of my derailleur. Once the circlip was removed, I loosened the barrel adjuster all the way, wiggled, pulled, tugged, and wiggled again, but it wouldn’t budge. Just as I started to get frustrated it magically sprang apart. I probably didn’t have something aligned correctly when I was tugging, and I should have inspected it more once it came apart so I could understand what was making it so difficult to remove, but I was too excited to move on with the project so I put the miscellaneous parts on my workbench and started fitting the new adjuster. The adjuster I got from Nathan was a paltry 2 grams including the threaded sleeve, the adjuster and the spring. There are two ways to look at this. The first is that it’s crazy to waste any time trying to shave off 4 grams from your bike, and the second is that the new barrel adjuster is one third the weight of the original. I opted for the second, figuring I’d come this far and I already had the parts.

Stock SRAM Red Barrel Adjuster Assembly

Stock SRAM Red Barrel Adjuster Assembly

I slid the new adjuster into the derailleur and it fit fairly well with no modifications. You could probably just leave it like this as the cable tension would keep everything together. But I decided I would sleep better if I bonded the threaded sleeve into my derailleur body so nothing would rattle and so that the sleeve wouldn’t turn when I adjusted the cable tension. I had some JB Weld lying around (it came with an old AlphaQ fork of mine) and it looked like it would do the trick nicely. I’ll bet that epoxy would also work fine, too. I cleaned the threaded sleeve and the hole in my derailleur, and then glued the two together. I let it dry overnight and in the morning threaded in the adjuster with the spring.

Tuned SRAM Red Rear Derailleur (122 grams)

Tuned SRAM Red rear derailleur (122 grams)

Drum roll please… The result? 122 grams! I guess there’s not much suspense in that seeing as it’s the title of this blog post, but oh well. The scale did flicker between 123 grams and 122 grams, so it must have been somewhere right in the middle.

Who cares how much your derailleur weighs if it doesn’t work well. Nathan had told me already that he liked the way his tuned SRAM Red rear derailleur worked with the carbon pulleys and the carbon plate, so I wasn’t too worried. He described it as being a bit more mechanical, more like Campy than Dura Ace, but that’s how I’d describe my SRAM without any modifications anyway. I installed the derailleur with my bike in my work stand and started to try to adjust it. I couldn’t get the derailleur to go into my lowest gear (biggest cog) and loosening the limit screw didn’t seem to have any effect. I then realized that the derailleur body was hitting the threaded sleeve I had bonded in because the threaded sleeve stuck out too far on the under side of the derailleur. I started to file it down but it was in an awkward and tight spot and it wasn’t easy to get a file in there. I ended up using a hacksaw to cut the excess threaded sleeve down, and then a file to touch it up, and my derailleur was back to working normally. If I were to do this again I’d cut down the threaded sleeve before bonding it into the derailleur. The one good thing about cutting down the sleeve was that my scale no longer flickered between 122 and 123 grams — it was a sold 122!

Back view of final tuned SRAM Red rear derailleur

Back view of final tuned SRAM Red rear derailleur

We’ve had quite a bit of snow in the past week and I haven’t actually ridden the bike yet, so I can’t tell you if the derailleur works well or not. In the stand, however,  it seems to work exactly like it always did. The carbon pulleys don’t have “float” like the stock pulleys, so maybe it’s going to be more finikey. I’m also not sure if the spring on the cable tension adjuster will provide enough friction so that it doesn’t migrate and make the derailleur slowly come out of adjustment. It will take some miles on the road under real world conditions to find out for sure.

Next on my list is to find out if the tuning parts I got from Nathan are available to the public or not. “dark_albert” is a bit of a mystery to me and I don’t know how one goes about buying stuff from him. But if you check back soon, I’ll be sure to add information on how well this thing actually shifts, and how one can go about buying the necessary parts to do the same.

I’d love to actually play with, test ride, and weigh one of those $1,200 Lightweight rear derailleurs. If the company claims 120 grams, it might actually weigh more than 122 grams. They are indeed beautiful, however, and maybe, just maybe if you’re the type of person who has foundations and sporting arenas named after you, you should go buy one.

6 thoughts on “122 gram rear derailleur

  1. You need help. Go out and race and stop talking about it.

  2. It’s true, I do need help. But my friends tell me exactly the opposite — they tell me I should ride and race less…

  3. what did you use to file / sand the Red derailleur? got a scratch on mine i am looking to smooth out…

  4. Hi Nico,

    Great job! I’ve read your experiment a couple of times, and liked the way the job turned out.

    I’d just like to say a few words in favor of the Lightweight RD :)

    I’m not an Sram owner but understand that the Sram road derailleurs only have one pivot spring. I.e. the upper pivot spring, the one at the bolt for mounting the RD onto the hanger, is missing on the Red, and present on shimano and campy derailleurs. Not that there’s anything wrong with it, Red seems to work fine woithout one.

    Just saying you need to compare apples to apples.
    Is the Lightweight RD also a single spring one?
    I think not, judging by the pictures that show a “hanger stopping tab” (is it called like that?) at around 3 o’clock of the RD mounting bolt. (far too much forward for a RD with an unsprung upper pivot.) The Red one , for instance, has that tab at aorund 6 o’clock compared to the same bolt, if positioned the same way as the lightweight pictured above…

    I think some builders opt for such 2 spring construction for smoother shifting? not sure though. Anyway I guess the Lightwieght RD has some extra structural elements compared to the RED.
    Remove those and the Lightweight will drop some more weight.. and -might- still function properly maybe less smooth.. or not at all any more :P

  5. I have my red down to 117g with a fairly conservative tune and it still operates flawlessly. The lightweight rear mech is debateable for flawless operation even at it’s full mass so cutting bits off such an expensive piece of kit is dodgy at best. The red simply does not need the spring within the mounting (pivot) bolt to operate perfectly so it’s a redundant comparison. Perfect is perfect.

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