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DT Swiss Ratchet Chipping

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DT Swiss Ratchet Chipping

Old 02-15-19, 08:14 PM
  #26  
unikid
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Or just switch to an Onyx hub or similar
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Old 02-16-19, 05:00 AM
  #27  
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For those that have not read the link to the engineering paper, it is a good read. The paper dealt with exactly the same type failure.

Even after reading it, I have no plans to move away from DT drive ring style hubs. Even chipped, this hub could be easily disassembled without tools, any debris removed, and the remainder of the drive ring would easily finish the ride.

As was mentioned, very easy to carry spare drive rings. At ETOR another captain asked about the DT hub on our Ventana. At the end of the ride, as I loaded the bike, I demonstrated the ease in rebuilding the drive setup. Removed the wheel, slips off the freehub body without removing the cassette. Removed both springs, and both drive rings. Wiped them clean with a rag. Cleaned the hubs internal sliding splines by wiping with a rag. Lubricated and reassembled. Reinstalled the wheel assembly. Total time, explaining as I did the work, 10 minutes max. Replacing drive rings is less since no need to clean the used ones.

Last edited by PMK; 02-17-19 at 06:05 AM.
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Old 02-16-19, 03:29 PM
  #28  
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Originally Posted by PMK
For those that have not read the link to the engineering paper, it is a good read. The paper dealt with exactly the same type failure.

Even after reading it, I have no plans to move away from DT drive ring style hubs. Even chipped, this hub could be easily disassembled without tools, any debirs, removed, and the remainder of the drive ring would easily finish the ride.

As was mentioned, very easy to carry spare drive rings. At ETOR another captain asked about the DT hub on our Ventana. At the end of the ride, as I loaded the bike, I demonstrated the ease in rebuilding the drive setup. Removed the wheel, slips off the freehub body without removing the cassette. Removed both springs, and both drive rings. Wiped them clean with a rag. Cleaned the hubs internal sliding splines by wiping with a rag. Lubricated and reassembled. Reinstalled the wheel assembly. Total time, explaining as I did the work, 10 minutes max. Replacing drive rings is less since no need to clean the used ones.
Thanks for pointing out the link; I had glossed over the post and wasn't paying attention. Reading now.

Yes, the field serviceability of the DT makes the Phil Wood "Field Serviceable Cassette" pale by comparison. Pulling the freehub body off by hand and being able to do trailside maintenance, lubrication and replacement is a BIG plus for these hubs. Couldn't agree with you more on that point. Just having a spare pair of star ratchets would have "saved" the OPs bike tour - or at least improved performance and let him sleep better at night!

I find it interesting that so much of the discussion centered on fatigue stress issues. Now I'm not an engineer and haven't absorbed the entire report, but it seems that tensile and yield strength issues, influenced by metal alloy choice, heat-treating, hardening and material uniformity would be the heart of the matter.

And they took their data from a single bike (Santa Cruz Blur) and a recreational rider:
"A biomechanical evaluation of the pedaling loads typical of a mountain bike rider were used to determine the cyclic loads experienced by the SRG teeth in the freewheel mode. Failure of the SRG was experienced after 6 years of use by a 36 year old rider, 183 cm tall and weighing 86 kg. The rider is self-identified as a recreational rider, averaging one off-road ride every week. Since pedaling data was not available for this rider, we utilized data made freely available through Strava.com, which reports pedaling power for an enormous set of trail rides, including the trails traversed by our subject."

I would add that the forces generated by a single rider on a single bike come NOWHERE CLOSE to the forces encountered by two riders on a tandem applying power to a rear wheel FAR LESS PRONE to losing traction.

So I'd be curious what their findings would be if they conducted this study on a mountain tandem. Because I'd expect the Star Ratchet Gear (SRG) failure to occur on the very first ride! So in other words, I would not expect fatigue issues to be part of the discussion at all. I say this because I went through the DT/Swiss SRG in very short order, before hardly any miles were on the hub, and especially on the replacements. Two riders on steep terrain simply overwhelm the SRG system.

And it just occurred to me that this issue will be exacerbated by the use of larger mountain bike wheels (27.5 and 29"). Whereas the hubs were designed when 26" wheels were the norm. Torque loads at the hub increase as wheel diameter increases, due to less and less leverage the wheel has as radius increases, given the same chainring/cog gear ratios. So ultra-low off road tandem gearing on 29" wheels should lead to even more hub issues. DT/Swiss may want to redesign the star ratchets for their tandem hubs.

I met Willie Hügi at Interbike just as I was having issues with the DT hubs. He said when the Hügi design was obtained by DT (from Union Fröndenberg), they redesigned the ratchets to take rider complaints into account. The deeper ramps on the Union/Hügi hubs caused REALLY LOUD freewheel noise during coasting. This was a common complaint I heard from customers, many of whom were known to poach single track during night rides when stealth was desirable. Well, Willie just threw up his hands and said, "Oh well, they wanted a quieter hub!" And thereafter I began meeting more and more single bike riders who were having problems with the DT rear hub. (One guy in Moab, ironically, where I broke a DT and a Phil.) Then I KNEW it was not the hub for my mountain tandem. (Again, the Union/Hügi hub on my road tandem has never had any issue whatsoever, so I'm pretty confident in that earlier design.)

Perhaps DT should simply go back to the Union/Hügi design for tandems. Sure, they're loud, but better that than catastrophic failure on a ride! And with 29" wheels, torque loads on hub internals are only larger now. (I'll add that this was always a potential issue on road tandems with 700C wheels , but since road tandems don't have the ultra-low gearing, nor to road rides hit terrain as steep as off road, torque loads never get as high, so failures never became epidemic.)

Thanks again for the link to the report. Saved it in my "hub failure" folder!
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Old 02-16-19, 05:09 PM
  #29  
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That paper is an amazing find. One thing that jumped out at me was the discussion of the chrome plating. Variances in that 10 micron layer could very well explain why only some teeth on just one of the ratchet gears could chip off. The fact that it can still support the forces driving a tandem up steep hills even when many of the teeth are chipped speaks to the robustness of the basic design.
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Old 02-16-19, 07:20 PM
  #30  
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Originally Posted by unikid
Or just switch to an Onyx hub or similar
+1 the Onyx Hub is of the Sprag Clutch design. Its proven clutch technology is Aerospace approved. It's probably the most robust clutch on the market. Used commonly in helicopter rotor drives!
Also, its freewheel/coast parasitic drag is the lowest of any bicycle free-hub available according to a recent test by a team at Duke University.
For those of you with reliability concerns and or Tandem MTB applications, give this serious look.
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Old 02-16-19, 09:09 PM
  #31  
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Originally Posted by bogriver
+1 the Onyx Hub is of the Sprag Clutch design. Its proven clutch technology is Aerospace approved. It's probably the most robust clutch on the market. Used commonly in helicopter rotor drives!

Also, its freewheel/coast parasitic drag is the lowest of any bicycle free-hub available according to a recent test by a team at Duke University.

For those of you with reliability concerns and or Tandem MTB applications, give this serious look.

I can't believe anyone makes such a bid deal about freewheel drag. If you don't want (a very little bit of) coasting drag, keep pedaling!


Not to badmouth the Onyx, but the drag advantage is pretty silly. And this is a hub that weighs 120g more than the King, so you're gaining a minuscule amount on drag, but carrying more weight up every hill. I'm guessing the weight penalty has a much higher impact on overall effort over the course of a mountain bike ride than a little bit of drag. And don't forget, the most drag a bike experiences is wind resistance. You'd be better off working on you aero positioning, wearing a skinsuit and aero helmet than worrying about freehub drag. (And this is why ceramic bearings are a cost/benefit loser in my opinion. Nice, but over the top expense at very little gain.)


But the weight penalty is worth considering; if it prevents high torque load failures. I made this exact decision when choosing Phil Wood over King; I hoped the weight penalty would be worth the added durability. But I discovered this was not necessarily the case. And King appears to have addressed the issue and offers a durable hub that has an excellent track record among mountain tandem riders. The Rholoff Speedhub has also proven to be highly durable; but again, with a considerable weight (and cost) penalty.


Plus, the more seals a bearing possesses, the more drag it has. And grease viscosity adds drag as well. So if you REALLY want to reduce drag, remove your BB and hub seals, use lightweight oil instead of grease, and upgrade your derailleur pulley wheels with cartridge bearings. Those things gum up and add drivetrain drag like nothing I've seen before! Problem is, you'd be sacrificing durability and longevity to gain a little reduction in drag. Rather pointless pursuit when, again, most drag a rider encounters is air resistance.


Not to be too much of a stick in the mud, but that's how I see it.
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Old 03-23-19, 03:29 PM
  #32  
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Resurrecting this thread as I was just cleaning gunk out of my DT Swiss 540 tandem hubs from a 2015 Cannondale road tandem that were making a squealing noise. All fixed and was easy with DT's online resources, however, I stumbled on this question of 18T verses 32T verses 54T ratchet rings. I read this whole trail hoping to get an answer on whether they worked for tandems but didn't get it. I need to service my freehub, it has the 18T ratchet rings in it now, is anyone running the 54T in their DT Swiss tandem freehub? Any issues? I like the thought of quicker engagement but we are a heavy team 390lbs including bike (but we are fast). Any issue with the smaller but higher number teeth? Thank you!
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Old 03-25-19, 01:34 AM
  #33  
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I spoke with DT and they said to stick with 18 as it’s the strongest setup.
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Old 02-11-21, 01:20 PM
  #34  
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Excessively heavy grease?

One of the responses mentioned an engineer from DT recommending lighter, cold temperature grease and I think I understand why. If heavy grease gets caught between the faces of the ratchet they might not fully mesh and engage. Being spaced apart by a layer of grease, only the edges of the teeth will engage, and under peddling force they would be subject to friction which would prevent subsequent settling into a full engagement. This means for a particular peddling cycle the ratchets would be only partially engaged for the duration and only at the edges of the teeth. This could create excessive load at the edges and failure.

To prevent this scenario I would be sure that spring was strong (stretch it out a bit?) and use the lightest grease or what DT recommends (they make a special grease for the star ratchets). That grease or oil has to *get out of the way* very quickly. For that reason I would also avoid packing the star ratchet mechanism absolutely full with grease. Void area could be important.

Last edited by autonome; 02-11-21 at 01:26 PM.
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Old 02-11-21, 06:40 PM
  #35  
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The DT engineer I spoke with advised applying the grease about as thick as the glazing on a donut.
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