Freehub pawl system vs star ratchet system

Question

If you were to choose between a Hope Pro 4 hub and a DT Swiss 350 or 240, purely based on their freehub types, ie Hope's pawl system or DT's ratchet system, which would you choose and why?

The main question is, which system is better, and why?

Just to be clear, these are the two types

Pawls System:

Ratchet System:

Nathan Knutson · Accepted Answer

Hope hubs are a very refined, reliable execution of the pawl design. They don't do much to illustrate the disadvantages of the concept that designs like the star ratchet are trying to address.

One potential downfall of pawl systems like Hope uses is that when things go wrong with them, either the pawls or the part inside the hub shell that the pawls engage, which I'll heretofore call the "drive ring" as it's named by some manufacturers, can become damaged. Typically the drive ring is a hardened steel piece threaded into the shell. Some potential scenarios:

If the pawl mechanism is underlubricated, contaminated, underpowered and/or imprecise, partial engagement between the pawls and the drive ring can occur. In this situation the pawls haven't sufficiently sprung up into the mating teeth of the drive ring at the moment the rider applies drive force. Instead the tips of pawls and the drive ring teeth ram into one another and may slip, potentially causing damage to either or both. Pawl-based drive systems can all do this under the right circumstances, it always has some destructive potential. It's also possible for issues with unequal spring tension, damaged or displaced springs, or other imprecisions to create a situation where some pawls get overloaded and become damaged or fail. Avoiding any such issue is one of the main goals of systems like the star ratchet.
There can be hardening problems with the pawls or drive ring. Sadly I've seen this on the drive ring once or twice on well-known, expensive, small production hubs, which were at least able to be warrantied. Issues of this sort are of course possible with other designs, but see below why it's painful with drive rings.

In either case, the teeth of either the pawls or drive ring can become chipped and deformed. At that point the problem can begin to build on itself. The teeth have to be sharp for the system to work as intended.

One thing about drive rings is that few manufacturers make them easy to replace if something does go wrong. When it is possible, either you need a new one plus a weird, expensive, proprietary tool that goes in and mates with the teeth, or in some cases you need to send your wheel in to the manufacturer. High-end aftermarket hubs and some wheelsets will typically give you one of those two options. Beyond that, neither option usually exists. You can find some high-dollar wheelsets where once the warranty period has elapsed, addressing a drive ring problem is difficult or impossible.

So while the drive ring is not technically a dynamic surface that's integral to the hub, in practice it might as well be in many cases, and my experience is they can be a little more damage-prone than people realize. Pawls and their hardware are typically more available, although sometimes they can only be replaced along with a new freehub body. And for older, lower end, or OEM hubs, they may be unobtainable.

More aggressive sealing and spring force are both design weapons against engagement issues on a pawl hub ever occurring. (Hope hubs take both pretty far). Reliability is increased at the expense of marginally increasing drag while coasting, the funny thing about coasting drag of course being that to a point, it's not a great concern in most riding disciplines where it's reasonable to split hairs about performance.

Systems like DT Star Ratchet and King Ring Drive, which I'm going to arbitrarily call "drive plate" designs, are trying to make partial engagement closer to being physically impossible, even with contamination and poor lubrication. Contact area is increased at every step of the torque transfer, and it's between two unified pieces, rather than separate pawls that are only as good at engaging all at once as their spring tensions are equal. Extant examples of drive plate hubs make all parts fairly easy to replace but very seldom need it, due to their efficacy at distributing load over more area. This quality is of heightened value in a hub one invests in with the intention of re-using indefinitely as rims wear out.

Pawl systems have an advantage at each approximate price point in the rate of engagement numbers they can obtain while still being reliable overall. At the high end, Industry 9 is a poster child, with ROE numbers down to 0.52°. Plate type systems have in contrast seemed to find their limit at 5-6° for a King or 240, presumably because their torque-transferring parts are smaller by necessity and so making the toothed/splined parts any smaller would sacrifice too much strength or otherwise become impractical.

Another way of looking at is that pawl and drive ring systems, and especially the highest performing ones, need to push everything to the limit in terms of materials, hardening, machining precision, matched spring tension, etc. The best ones are only the best because of how close they fly to the sun. Plate systems don't have that dynamic, but at least as far as what exists to date, they take a little hit on rate of engagement potential.

I personally feel that between the Pro 4 and 350 freehub, both are reliable but the star ratchet design gets there in a way that's more elegant and robust. But, the 8° ROE on the Pro 4 versus 18° for a stock 350 would be a reasonable deciding point. Different riders value ROE very differently, and for good reason.

ojs · Answer

Both work fine. Technical explanation would lead to endless debate between people who don't know what they are talking about, so I'll go for economical one instead.

The patent for DT style star ratchet expired in 2015 and Chris King ring drive in 2017. Unlike innovations such as cassette freehubs, threadless headsets or three piece cranksets, other manufacturers haven't rushed (1) to build these once patents expired or were worked around. This suggests that these mechanisms aren't a huge improvement over the common ratchet and pawl design. On the other hand, these designs have been manufactured and sold at premium prices profitably for 25 years, so they can't be significantly worse either.

(1) Zipp has introduced their own variant of star ratchet after the patents expired. They are the only one that I know of. This might point to the direction that some star ratchet benefits might be real but it is too expensive to manufacture for common use.

Criggie · Answer

Small considerations

1) which one will have spare parts available in the future, should you need them?  That's very hard to guess at this point.  You might need to buy a new freehub to support a different sized cassette someday.

2) sound - some riders are all about the sound of their freehub as it coasts.  It makes no difference to me cos I generally soft-pedal all the time, but some people like a loud clatter and some prefer a faster vizzz noise.  This has no effect on function, but can be used in racecraft when trying to psych out other riders.

bradly · Answer

I would consider ease of maintenance a factor in your decision regardless of ratchet style. Obviously from the vast supply of information above, you get the idea that it is primarily a matter of taste and budget that will inform your final choice, as both styles have their strong points and weaknesses, but consider that I have to do routine cleanings of my Chris King hub using proprietary tools that were pricey, I think I recall paying around $160. I use my DT Swiss 350 hub on all the same trails, ride styles, etc, and I clean it less frequently, and even still it never diminishes in performance as it gets gunked up like my CK hub, and it doesn't require any tools to clean other than an old tooth brush and degreaser. The DT Swiss design is mechanically simpler and less expensive. I actually like how it performs better than the Chris King Classic. Most good brands float solid, quality equipment that works great when well maintained, but how mush hassle it takes to do so is a giant factor for me.

Answered by bradly on January 26, 2021

Mark Visser · Answer

Star Ratchet is better for a number of reasons.

Synchronization / loading a single pawl - With a pawl based system (as others have pointed out), there is the potential for one of the pawls to engage out of sync with the others. When this happens, the freehub body gets pushed off-center, which loads up the freehub body bearings to the point where they can become damaged. If they're damaged, then they have more play, and the likelihood of a pawl to engage out of sync goes up further.
1b. Synchronization - because a star ratchet system has all the teeth on a single piece, the likelihood of them not engaging properly is much much lower than a pawl based system

Self centering - A star ratchet system, when engaged, will pull the two drive rings centered to each other (due to the geometry of the teeth / the fact that they're distributed radially out from a single center point). So the exact flaw that can destroy a pawl based system can not happen in a star ratchet.

Points of contact - A star ratchet has 18 / 24 / 36 / 54 teeth, of which ALL of them engage every time. A pawl based system will have up to 6 pawls. Even if the pawls are multi-teeth, each pawl still only has one point of contact in the pawl pocket (where they sit in the freehub body).
3b. Points of contact 2 - The outside diameter of the star ratchets have 26 splines on them. Again, much larger surface area to spread the load over.

If you want an interesting case study on this, look at fat bikes. The failure rate of pawl-based freehubs on fat bikes is insane.
This is due to two issues. The tires offer immense amounts of traction, so the torque being transmitted is higher than ever, and the axles are quite long, so they flex a lot more. This means that pawl based freehub bodies are suspect to synchronization issues, and if you ever load up a single pawl, it's likely game over for that freehub body.
Now a beef - the new Hydra from Industry Nine. It intentionally uses mis-synchronization to offer even more points of contact (690). It engages 1 of 6 pawls, and then as the system flexes, the 2nd pawl will engage, and then the 3rd and so-on. I imagine that they will chew through freehub body bearings at an alarming rate.
Now a second beef - everyone is chasing high points of contact or low degrees of engagement. That's fine on a hardtail. On a dual suspension bike where suspension action often has an impact on chain length, these high points of contact can cause a lot of kickback at the pedals, where it would be unnoticeable with a lower POE.

juhist · Answer

Let us revisit what the goals of a freehub are:

To transmit rotational forces reliably in one rotating direction only
To do so silently
To do so with minimal backlash (quick engagement)

The star ratchet isn't very good according to those criteria:

Reliable
Noisy as hell
Backlash the same as the tooth angle difference in the ratchet rings

The pawl system is much better:

Reliable, unlike what the star ratchet fans would like you to believe
Can be made silent
If there are 4 pawls, it is possible to offset them in such a manner that backlash is one fourth of the angle difference in the ratchet ring

Based on these, a good implementation of pawl system is the superior choice and
even the worst possible implementation of the pawl system is better than a star
ratchet.
Unfortunately, many pawl system implementers fail to see that elasticity of the
mechanism causes only one pawl and tooth to handle all of the load at a time.
Thus, for example a system of 4 pawls is often designed in such a manner that
all pawls engage at the same time, meaning the backlash is the same as the
angle difference in the ratchet ring. This symmetrical placement of the 4 pawls
achieves nothing (the intention is probably that all teeth would distribute the
load evenly but due to elasticity it won't happen) while at the same time
maximizing backlash.
Often times, star ratchet is much more expensive too. It is mainly made by DT
Swiss at a great expense. For example Shimano hubs have a much better silent
pawl freehub body and the right side bearing in Shimano hubs is very close to
the right end of the axle, minimizing axle failures. Furthermore, Shimano hubs
are far cheaper than DT Swiss. Of course this doesn't mean that all pawl hubs
are cheap: certainly there are pawl hubs ten times as expensive as Shimano but
not ten times as good.
Also, it is worth mentioning that no matter what freehub system you have, the
freehub body must be made of steel. An aluminum freehub body will have the
sprockets dig into the aluminum. So if you have a choice between star ratchet
with steel freehub body and pawl system with aluminum freehub body, you are
better of selecting the steel one.
Similarly, there are other considerations when selecting a hub too. One of them
is the material of the axle: it should be chromium molybdenum steel. Any hub with
aluminum axle will break in no time. Also hubs where the right side bearing is as
close to the axle end as possible should be preferred, and cup-and-cone bearings
should be preferred over industrial cartridge bearings because the cup-and-cone
bearings have a full complement of balls.

Freehub pawl system vs star ratchet system

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