Have you noticed that the inners of the hubs look very different than they used to look? You may have if your new wheels cost $2000 or more for the pair and if you had occasion to see the inside of the cassette assembly. In traditional hubs 3 or 4 spring loaded pawls engage a ratchet or drive ring. That ring looks like a gear, but the teeth are on the inside of the gear, facing inward. This new ratchet-style design features a pair of gears, called star ratchets, that engage with each other, as you can see from the images of a DT Swiss DICUT hub.
This design is called a “ratchet-style” hub and when this tech it’s deployed it replaces that “pawl-style” hub. The one confusing bit of terminology is that that inverted gear that you see on both pawl-and ratchet-style hubs is called by some a "ratchet ring." Oh well!
The function of either style hub is to allow your hub to coast when you’re not pedaling, and engage and drive the wheel when you are pedaling.
If you’ve ever heard of the Hügi hub these were the first ratchet-style hubs. The design sprung from the brain of Swiss inventor William Hügi and DT Swiss bought Hügi – the hub company – and with it the patents. The reason you’re seeing so many ratchet style hubs in wheels these days is those relevant patents recently expired. (When you see everybody jumping on a design bandwagon after a patent expires you realize the patent holder was right all along.)
Former pro triathlete – and now Road Market Manager for DT Swiss – Ralf Eggert wrote to me that the general function of the ratchet system found in certain of today’s DT Swiss road and gravel wheels remains almost unchanged from the DT Hügi hub. Here is a video from DT Swiss showing how the hub works.
As you see, there are two gears that interact in a ratchet style hub. This is the design so many of the wheel companies are now moving to. In all the hubs these companies are making today this is the case, except that DT Swiss has recently moved to a new design that has only one ratcheting gear. “In 2019 DT Swiss introduced the Ratchet EXP freehub technology with one threaded Ratchet firmly screwed into the hubshell,” Rolf wrote to me. “With Ratchet EXP only one Ratchet rotates, but the engagement is the same and quicker. Also, the bearing distance inside the hub was increased, as the bearing is located inside the threaded Ratchet. This means more stiffness for the axle.”
Whereas most wheel companies have kept the deployment of this hub style to its upper end wheels, DT Swiss has develop a ratchet style hub for much lesser expensive wheels. These wheels feature the RatchetLN freehub system, which replaces the 3-pawl-system even in DT Swiss hubs that'll go into entry level bikes. But currently, the Ratchet LN is available for MTB products (hubs and wheels) only. For Road products, this FH-technology will follow in late 2022.
Above is the style of hub you’re probably used to owning. What you see here are variously called cassette assemblies, or driver bodies, and they are generally interchangeable. They share the same inners, but the cassette body is either a Shimano style or perhaps a SRAM XDR style (if it’s for 12 speed), and it's SRAM XDR driver body you see used in the DT Swiss video above. These driver bodies above have 3 and 4 pawls respectively, or up to 6 pawls, and you can see both a 3 and a 4 pawl driver body above, made by different wheel brands. This is the design these new ratchet-style hubs are gradually replacing.
What companies are moving over to ratchet designs? ENVE uses the Mavic ID360 ratchet in its hub, and only for road and gravel applications. This system has a 40-tooth, 9-degree engagement. I just added a level of complication there, didn’t I? This is the state of where things are in ratchet style freehub systems. Engagement angle is a hot topic, but mostly in MTB. Road riders don’t need to worry about this much. Just as with pawl-and ratchet ring systems riders are always looking for a quicker engagement, likewise in this new hub style by increasing the number of teeth in the star ratchets.
DT Swiss uses, for road style hubs, anywhere from18 to 36 teeth. The 18-tooth ratchets have an engagement angle of 20 degrees (20° x 18 = 360°) and means that there will be up to 20° of pedal turn until the teeth engage. In the recent new releases DT Swiss has deployed star ratchets with 36 teeth, so, that’s a 10° engagement angle. If you look at what ENVE’s doing, 40 teeth times 9° equals 360°.
So, more teeth means quicker engagement. On the other hand more teeth mean more wear in the idle freewheeling position when descending or rolling towards a turn. To prevent premature wear companies use a special grease with low viscosity and which does not spread by centrifugal force. This is why wheel companies exhort you to not grease this system with just any grease.
Shimano calls its deployment of this style Direct Engagement, and you’ll see this deployed in the hub pictured just above. I wrote about this hub when I wrote about Shimano’s new Dura Ace wheels. I like Shimano’s expression of this design because it mixes is a little old style ball-and-cage bearing design, which allows users to choose the weight of the grease in the bearings, and to tighten the bearings (via a pair of cone wrenches) to a precise degree. You’ll find Direct Engagement only on the new Dura Ace hubs as well as XTR and XT mountain bike hubs.
Shimano didn’t simply move to this design without testing. It created prototype hubs that purposely had or lacked lateral rigidity, vertical rigidity, or driving rigidity. Almost all of the riders favored the prototype designed to enhance driving rigidity, from which Shimano gleaned that this was the design imperative to follow.
Zipp has a trio of hubs that you’ll find in its premium wheels. There are 3-pawl and 6-pawl designs, but at the top of the heap sits the Cognition hub, which features what Zipp calls its Axial Clutch system. This is a Zipp’s take on the ratchet-style design, and there’s a video here that shows it pretty clearly. The image just above is a screenshot from that video, which is pretty cool, and demonstrates how Zipp used magnets in place of springs. Zipp has been producing that hub for 5 years, and was one of the first non-DT Swiss companies (that I know of) to embrace tech like this. This is because Zipp's Cognition hub does not infringe on the DT Swiss patent. In recent years the magnets have migrated out of Cognition hubs, since replaced by a Sylomer wave spring. One other major difference in Cognition hubs is the diameter of the system is larger, with 54 teeth in the ratchets, or gears, versus the more typical 36 (or 40 as we see in ENVE's case).
CADEX and Reserve (this is the wheel brand most often on Cervelo and Santa Cruz bicycles) are also using this new hub style and the list of brands heading this way goes on. You won’t see this hub style in inexpensive wheels for a while (other than the version DT Swiss has planned) because it’s not simple to make star ratchets. For example, that single-star-ratchet design of DT Swiss, the Ratchet EXP, experienced some surface finish issues that lead to premature wear and grief for users of some hubs. The star ratchet had to be replaced in affected wheels. Live and learn.
Because some of these wheels feature end caps that just pop off – no tools needed – I’ve had wheels just kind of fall apart in my hands. The cassette just falls off, along with the hub inners. If this happens to you with a ratchet style hub, just look at the images and videos here. There’s a spring on each side, and in between the springs are star ratchets that engage with either other. Pick it all up off the floor and reassemble.