Kirk Pacenti Cycle Design polygon cassette freehub body open source standard for bicycle hubs

After selling his business recently, Kirk Pacenti has been busy working on new ideas. His latest? An improvement to the age old cassette freehub body. Arguably, this piece has seen little or no innovation other than materials in quite a while despite the common frustration of an expensive cassette wearing grooves into and getting stuck on a very expensive lightweight alloy freehub body.

Pacenti has a solution, and he’s putting it out there as an open source standard for anyone to use. We think it looks pretty solid. Here’s what he thinks:

I want to make clear that it doesn’t have to be my design. The real point is to get the industry talking and working together on a standard.

I look at it this way; 10/11 speed systems are “line in the sand” of sorts. Now that we’ve crossed it, we may as well optimize the system for that many cogs rather than stuffing them into an obsolete 7/8/9 speed standard.

Splines also have to go, as they were designed when cassette bodies were all made from steel. With a polygon shape you could conceivably make much lighter cassette bodies, possibly even made from composite materials.

Another pic and more info after the break…

Kirk Pacenti Cycle Design polygon cassette freehub body assembly open source standard for bicycle hubs

The polygon shaft design is used heavily in industrial and automotive arenas and is proven to handle much, much higher torques than you or I are ever going to put out. Pacenti says he’s been tinkering with this concept for about four years and thinks it could realistically move into production by 2014/15. Given that most high end hubs have easily replaceable freehub bodies, retrofitting this design should be no problem. Getting the cassette manufacturers on board is another story…but if someone (KCNC, Samson or even Pacenti himself) moves forward with a lightweight cassette and body combo that’ll work with a few popular hubs, we think the large manufacturers would follow suit if a market materializes.

What do you think? Would you be an early adopter if a retrofit/upgrade kit were available for your wheels/hubs?


  1. Another good idea from Pacenti. Who would be into it?

    Yes- Every independent hub/wheel manufacturer and SRAM

    Probably Not – Shimano and Campagnolo

  2. I think the threaded 68mm BB shell is more antiquated, outdated and problematic. And Shimano and Campy are pretty staunchly set there. There is much more to gain by revolutionizing (and unifying) BB technology than cassette splines.

  3. This is better than BB30, oversized headsets, BB386EVObullshit and Firecrest…combined. Here’s to hoping the industry can align and agree on something, especially before the UCI takes over we are forced to resort to single speed steel frames with U-pull brakes and toe straps.

  4. Wouldn’t it be nice to not have to shimmy the cassette off and on? And simply throw the thing on without having to take the time to install it like a puzzle?

  5. Excellent idea. Would also make it easier to get the 9t cassette cog movement off of the ground for those of us that want to use a single ring and ultra-wide range cassette – such functionality could be designed right in.

  6. @Jeff and Matt

    It simply looks like a ‘curve of constant width’, a kind of shape that’s been applied since well before e*thirteen. If that’s proprietary then someone better claim ownership of the square and circle too.

  7. I’ll start working on a cassette extractor tool! they can be different spline tools for each manufacturer.
    this is stupid

  8. I am glad to have someone with a voice for logical change like Kirk Pacenti. There are many of us that wish for improved standards for various parts in the bicycle industry, but unfortunately we don’t have a recognized name like Kirk does – so our ideas go unnoticed. By making it open-source, it would hopefully prevent all the arguments & litigation over patents & proprietary designs. Obviously, I’m for it!

  9. Thanks for the support. I think the idea has merit and some large companies are looking at it as we speak.

    The goal is to create a new standard for the 2014/2015 model year. Hopefully it would allow for a single 10/11 speed standard with room for more cogs down the road. (you know it will happen) I also want to be able to accommodate 9t cogs if possible.

    As for the shape, there is nothing proprietary about it. It has been in use since the 40’s in many different industries. This shape would likely make manufacture of free hub bodies and cogs less expensive because of the reduced complexity.

  10. Pacenti has been “tinkering with this concept for about four years and thinks it could realistically move into production by 2014/15.” Really? Is anyone as unimpressed by that as I am?

    Yes, you could replace splines with something else that you stole off a crank-maker’s website, but what are the reasons you should? Just what would this design offer that we don’t already have? It needs to be valuable enough to convert to an incompatible standard.

    It would seem like 4 years of tinkering should yield more than an idea that we could do something else, but Pacenti is more demagogue than engineer.

  11. It’d be great if this “standard” gained traction, but I don’t see that happening, at least not for a long time. SRAM, Shimano, and Campy all want to lock their customers into their brand as much as possible. The only possible downside might be in the expense to manufacture it. Some component manufacturers might have to invest in new, more expensive tools, and without knowing what current tolerances are on cassette hubs, it’s difficult to say what the tolerances will need to be for this freehub. Still, those things can always be overcome. Given a sufficient range of cassettes and compatibility with other hubs, I’d buy it.

  12. Not sure how removal of the cassette would be much easier. The Groovy cranks use a pinch bolt design, while the e13 cranks have a self-extracting crank bolt to remove the non-drive side crank arm. Would this design require a press fit, or would the machining tolerances have to be super precise? I’m just not entirely sure how this design functions compared to other Reuleaux triangle designs. Maybe we could get a follow-up explanation from Pacenti?

  13. Steve, if you’re having that much trouble installing a cassette onto a freehub body, you may want to drop cycling in favor of golf. golf is a sport you can do while smoking a cigar. and now the golf purists will howl. purists love to howl.

  14. I think Hope came out with a better solution IMO…Integrate everything with the hub..make it 1 piece.
    Of course, this couldn’t be a “standard” because almost every freehub system is different, but I think it’s the best idea I’ve seen in a long time!

    I don’t really see Shimano or SRAM taking this design and making it THEIR standard…probably Industry9, hope (50-50) or companies that machine In-House. Great idea though!

  15. @secondtimeuser
    you know if you just did sram with 11-36 cassette and a 53 tooth up front you can actually get a wider ratio than a standard 53-39 x 11-25. Also a 9 tooth cassette cog would put massive friction on the chain.
    If you really want to be a weight weenie you might as well just look at specialty/custom ultra low weight parts or a lighter something else instead.

  16. Er teh puzzle like cassette assembly from what I can tell is much to do with using multipiece designs that have to be assembled in the correct fashion to get shifting to work.

    SRAM road cassettes almost seem to have a missing tooth that’s in a spiral form around the cassette so that would have to be rectified.

    Really the only incompatibillity that exists is between Campagnol and Shimano, and that only relates to 11speed I think as you can run conversion cassettes for 10 speed.

    Surely the obvious way forward is the thing that Hope are doing with a cassette body and cassette in one pece certaily for high end stuff?

    It’s a nice idea though…

  17. @fleche1454
    The goal of a 9T cassette isn’t to use it with a 53-39 road crank as a weight weenie part. Interest in 9T cassettes is with mountain riders who want to switch to single chainring and get even wider range than 11-36. 400% is a lot more flexible than 327%. I agree with secondtimeuser, supporting 9T and 10T cogs would be a win, roadies don’t need to use small cogs if they don’t want to.

  18. @craigsj “you could replace splines with something else that you stole off a crank-maker’s website”

    See my earlier post. This kind of shape (which has infinite variants) is as old as dirt and used in all kinds of applications.

    @pdxley “Would this design require a press fit, or would the machining tolerances have to be super precise?”

    No more of either than current cassettes – if there is any play in current cassettes then it disappears under load, which is why the freehub splines get notched. With this design, any play would also disappear under load, but no splines to get dug into the same way.

  19. Just a quick note on the hive / e*thirteen polygon design: our BB interface is based on the DIN polygon standard, which is described in the machinery’s handbook, among other places. We don’t claim to have invented it. Our interface is proprietary because we started with the standard polygon shape and changed it to suit our application. We don’t claim to own anything to do with polygon couplings other than our own implementation of the concept.

    Using a polygon for the freehub body interface is an interesting idea – we’re looking forward to seeing what develops!

  20. i like the concept of lighter, strong…but as many have already commented it really depends on the implementation of the cassette body. if its easy on/off and doesn’t looses less power under load with no greater wear issues that the current spline design…i’d be interested.

  21. I need to see tangible benefits before making such a change. Otherwise, I would do something like this simply to show it off at the trailhead.

    It’s the same reason people ride Jones Bikes–no benefit whatsoever other than having a reason to strike up conversation at the trailhead. People with few friends usually get such bikes.

  22. I don’t think I would bother with the upgrade of an currently owned hub. But I wouldconsider it when replacing a wheel/hub.

    @Varaxis and dhbomber: what you’re basically looking at is a modern interpretation of the freewheel. But in the Hope design although it saves weight (their primary goal) it adds huge cost to the part.

    I like Pacenti’s vision, but it doesn’t do enough. What I do appreciate is his voice: “I want to make clear that it doesn’t have to be my design. The real point is to get the industry talking and working together on a standard.”

    IF anything this is a better, more forward thinking perspective on the issue:

    I just hope all this doesn’t lead to 20 ridiculous “standards” as is the case with BB’s and headsets

  23. Terra Forma Evolution hubs also have some inovative hub ideas. They use the space under sram powerdome cassette to place the bearings wider and use a much larger engagement system than a regular hub. I’ve never tried them but they look like an interesting cocept. Very spendy though.

  24. the amount and ferocity of responses of long-time riders & mechanics here should be a good indicator that there is a lot to be said for the re-think here. and you can count me among them. old gouged-out splines have to go. and i, for one, <3 open source. it made bb's better… maybe a trifling bit volatile as everyone tries to out-think one another and claim small bits of superiority, but ultimately we must hope that a reasonable new standard can be agreed upon–one that home mechanics can work with consistently for a reasonable length of time (3-10 years?), and that can provide dependable performance for committed/competitive riders and service professionals at a competitive price.

    kudos to kirk. the industry & culture could use more free-thinkers like him.

    Gillis makes some great points above, too.

  25. So Terra Firma evolution really just evolved the old shimano screw on freewheel using a sram cassette sticking more teeth in there and some cartridge bearings

    How about an innovative company engineers a product that takes the design of the whole bicycle into account and not just the bits company A B or C decided to bolt to it which now BTW contain so many compromises that they are just about survivable

    I hope the design of freehubs follows bottom brackets where the first the real evolution was putting a bigger axle and bearing in it it just goes to prove bicycle design is a joke and lead by marketing hype .

    The only downside is that pacenti seems to genuinely want to make a better bike maybe pull out your pens and pencils and just do the whole thing would be a step change the industry needs not incremental dilutuion of every standard going

  26. Pfft, in the end, I hope derailleur based shifting gets phased altogether. Have the cranks transfer power to a gearbox, which then runs a chain down to a singlespeed rear wheel.

    Miniaturize the gearbox enough for weight savings and to not bang up our legs on. Maybe narrow the rear end a bit. Maybe you can change the main pivot to be higher, aligned with the chain coming from the gearbox and enjoy a rearward arcing axle path for better response to square edge bumps, yet still maintain good pedaling characteristics.

    Next up, add speedometer/ and tachometer (cadence meter) and create automatic shifting. LOL. Getting closer and closer to just making a motorcycle with human power.

  27. Grove used the tri-lobe design for crank spindle in 1978 for their HOT Rod cranks, the first modern two crank piece design (pre dating bullseye). Groovy had recently licensed and re-vamped the design for the new Hot rod cranks, using the same spindle interface using a pinch bolt. E13 borrowed the idea from Groove & Groovy used a modified “press-fit” version of the same idea. While Grove was the first to use it in a crank spindle application, and E13 obviously borrowed and slightly changed the fastening design, neither claimed to have invented it. Both were based on an existing DIN torque shaft interface standard used in motor/drive applications. It is an excellent torque transmitting shape with much greater surface drive contact than splines or straight sided polygons. The design is just as sound for “slip-fit” applications like cassettes. Cassettes now use slip fit splines, analogous to presfit crank splines like Isis, or Octalink. A slip fit tri lobe design, held in place with the same lockring we use now would be just as sound.

    My only question woudl be how to handle the “timing” of the individual cogs. Current designs use a single larger spline to ensure all the cogs are aligned properly. would you use a notch, or single spline to “line-up” the cogs?

    If it works elsewhere on a bike, why not re-apply it to another bike part? Current design has a problem. It was fine when both cogs and carriers were all steel, the notching wear was minimal. Now with so may aluminum, or titanium carriers, combined with cogs made from similar softer/lighter materials, the notching and wear of the splines is a problem that could use some addressing. This would open up more material possibilities for carriers and cogs too.
    Obviously, a single piece cog/carrier (like current single speed BMX drivers) could be stronger/lighter but would be much more expensive (SRAM XO and RED casettes for example). If it does go forward, i’m sure the market will chime in with a few “better” new standards, which will just make for consumer’s, and mechanic’s frustration and marketing hype that will muddy the water, clouding the original good idea.
    Doing it as an open standard is a good way to help prevent this.

COMMENT HERE: (For best results, log in through Wordpress or your social media account. Anonymous/fake email comments may be unapproved or deleted. ALL first-time commenter's posts are held for moderation. Check our Comment Policy for full details.)

This site uses Akismet to reduce spam. Learn how your comment data is processed.