[Nexus gear hub] Ratchet+pawls vs. roller clutch?
Hello,
The page on Nexus 8 gear hubs on Sheldon Browns's site says that low/high-end hubs differ on two points:
Thank you. https://cimg8.ibsrv.net/gimg/bikefor...df48d9280a.png -- Edit : After more reading, it looks like… 1. Only rather old Shimano Nexus hubs use pawls + ratchet on the left instead of a roller clutch 2. Roller clutches are what transmit the energy to the hub ultimately and, thus the wheel, so it's not a good idea to grease the surface of the rolllers — or only slightly — as they will then lose traction. https://cimg1.ibsrv.net/gimg/bikefor...8ec583153e.png |
Originally Posted by Winfried
(Post 22396626)
2. Roller clutches are what transmit the energy to the hub ultimately and, thus the wheel, so it's not a good idea to grease the surface of the rolllers — or only slightly — as they will then lose traction.
Roller brakes, also, run in a greased environment and function (reasonably) well. |
I agree, although in this article, the user complained of malfunction after applying too much grease (just on the rollers? Also the gears?).
Still, am I correct in understanding that the rollers are indeed how the force goes from the cog to the ground through the gears and the hub? I'm surprised it all works simply by having the rollers push against the walls of the hub. -- Edit: It appears that the Nexus 7 has no roller clutches, and relies on two sets of pawls to rotate the hub: https://cimg3.ibsrv.net/gimg/bikefor...2ee0c42971.png |
Originally Posted by Winfried
(Post 22398252)
I agree, although in this article, the user complained of malfunction after applying too much grease (just on the rollers? Also the gears?).
Still, am I correct in understanding that the rollers are indeed how the force goes from the cog to the ground through the gears and the hub? I'm surprised it all works simply by having the rollers push against the walls of the hub. -- Edit: It appears that the Nexus 7 has no roller clutches, and relies on two sets of pawls to rotate the hub: https://cimg3.ibsrv.net/gimg/bikefor...2ee0c42971.png If you use either Shimano Nexus grease, or oil, you should experience no such issues. |
Thanks for the feedback.
|
Roller clutches are an old idea and have been used in niche applications in bicycles for a long time. They're silent, but have a little more parasitic drag than ratcheting pawls and have a spongier take-up feel.
Shimano introduced a 'silent freehub' a quarter-century or so ago. It was met with a yawn by the derailleur crowd*. I believe it's still available as part of their parts groups for law enforcement bikes. *There are even boutique freehubs that use the amount of noise they make as an advertising feature. Go figure. |
Originally Posted by Winfried
(Post 22396626)
1. Only rather old Shimano Nexus hubs use pawls + ratchet on the left instead of a roller clutch
https://cimg6.ibsrv.net/gimg/bikefor...52b818d526.png |
The "silent free hub" did find a following in the IceBike groups for cold weather riding. Shattered pawls are no fun at -40!
|
Apparently, the amounf ot noise made by pawls can be lowered depending on the material used as well as the number of pawls involved, among other parameters.
I do like how silent Alfine/Nexus hubs are on my bikes. I find the SG-8R31 more draggy than the SG-C6001, possibly because of the use of plain bearings vs. needle-bearing pinions. |
Originally Posted by Winfried
(Post 22398371)
I find the SG-8R31 more draggy than the SG-C6001, possibly because of the use of plain bearings vs. needle-bearing pinions.
https://cimg2.ibsrv.net/gimg/bikefor...39f9dcc828.png |
|
Originally Posted by Dan Burkhart
(Post 22398314)
Roller clutches are sensitive to the film strength of the lubricant which is the reason Shimano formulates their own semi fluid grease. When someone experiences these issues, I suspect it is because they use a more viscous grease which will hinder the engagement and traction of the rollers.
If you use either Shimano Nexus grease, or oil, you should experience no such issues. The oil is Royal Purple 75W-140 Max Gear. Interesting explanations of roller clutch operation It would seem that it's not the function of the lubricant to actually transmit the force passing through the clutch. |
My SA XL-RD5w has easily done up to 46 mph. I can feel the woosh on any hill.
Rohloff14 has done 43 mph. Nexus 7i won't top 38.1 mph. But that's with a boat anchor roller brake. SA RD3 feels the same as the 5w and went 37.18 mph, mostly coasting because only 92.5 GI. The SA pawls show maybe 1/1000th wear after 9,000+ miles. I don't remember any of my 50/11T defaileur bikes going over 40. But 2 of them had a mechanical speedometer. My SA hubs use 10-30w non-detergent lawnmower oil thickened with 25% Wynn's old car oil conditioner. NOT dipped. SA hubs are easy to take apart fully. I haven't taken the Nexus apart, except for the left bearing. |
36 hole, 3 cross...on what? A 20 inch folder? Dang. That's some serious lacing on the OP's wheel. Edit: never mind. That pic is lifted from Aaron Goss's shop in West Seattle.
Roller vs pawls. Who cares? Neither is better or worse. Roller is how car starter motors are done now. It is clearly the better design for low maintenance reliability & longevity. Pawl are best for firm instantaneous engagement. Simply different design priorities. IME neither makes a hill of beans worth of difference beyond the margin of error. I like my Nexus 7 with roller brake. I like my Rohloff. When fully broken in, I guarantee you neither is distinguishable from the efficiency of a well lubricated derailleur system in terms of system efficiency in actual use. If you can not go fast, look to other factors beyond the IGH. The IGH is not the reason. 3% of 200 watts is 6 watts. It's the amount of aerodynamic drag caused by exposed cable housing at 40kph. IOW: Meaningless. What's the OP's question? How to rehash Harris Cyclery friends site pages (avdweb.nl) & Sheldons IGH observations? Lame. |
Originally Posted by sweeks
(Post 22399312)
The Nexus hub gets its innards dipped in a synthetic gear oil once a year.
So there's no significant difference between the Nexus/Alfine hubs in terms of efficiency, and the use of plain/needle bearings and pawls/roller clutches is just marketing? Once its new cog gets here (hello covid), I'll open up the SG-8R31, see how lubricated it still is, experiment with either fresh grease or oil, and see if it makes a difference. |
Originally Posted by Winfried
(Post 22399597)
What gear oil do you use?
If you want to separate the big (drive-side) bearing from the gear cluster, you have to disassemble the right side. This is not necessary, in my opinion, but does allow for a more thorough cleaning of the bearing. After the oil dip, I lubricate the bearings with Shimano Nexus Hub Grease, which looks like a molybdenum disulfide type of grease. It eventually bleeds into the gear cluster, probably helped along by the gear oil. I don't see any wear on the bearing surfaces, so things seem to be working. Also, the grease/oil combination has no adverse influence on the roller clutches' performance. One of the things I don't like about the Nexus hubs is that they aren't well-sealed against the oil leaking out, especially from the drive side. So if your bike spends any significant amount of time on its side, it should be the *non-drive side* or you may have a small pool of oil. Since these hubs are originally lubricated by grease, not oil, the hub design can't really be blamed for the oil leakage. The bottom line is that if the bike spends most of its time in the upright position, oil leakage is minimal. A longer draining time after the dip helps; there's still plenty of oil coating the gears.
Originally Posted by Winfried
(Post 22399597)
So there's no significant difference between the Nexus/Alfine hubs in terms of efficiency, and the use of plain/needle bearings and pawls/roller clutches is just marketing?
https://cimg5.ibsrv.net/gimg/bikefor...6c31d7c0f.jpeg There is a syringe epoxied to the bottom of a plastic ice cream jar. https://cimg9.ibsrv.net/gimg/bikefor...fe20d7b5f5.jpg The syringe accepts the axle of the gear cluster, greatly reducing the volume of oil required to submerge the cluster. https://cimg0.ibsrv.net/gimg/bikefor...5ccd5bff05.jpg This can makes a nice base for the modified jar. The level of oil is sufficient to completely cover the cluster. I re-use this oil, adding more as needed. |
Thanks mucho for the infos.
While I'm at it, I'm thinking of drilling an oil port on the hub, and make it a breeze to add oil later à la Alfine 11. |
Originally Posted by Winfried
(Post 22400003)
While I'm at it, I'm thinking of drilling an oil port on the hub, and make it a breeze to add oil later à la Alfine 11.
|
From what I read, recent models of the Nexus 8 don't leak much provided you don't use more than ~15ml of oil. The Alfine 11 uses 25ml.
As for resting the bike, especially a folding bike, it's not clear it should rest drive side up or down. I read both. https://www.astounding.org.uk/ian/hubgear/oilport.html |
Originally Posted by Winfried
(Post 22400523)
As for resting the bike, especially a folding bike, it's not clear it should rest drive side up or down. I read both.
I tried wrapping the drive-side seal in electrical tape after thoroughly degreasing the outside. The gear oil found its way through in a few days. What seems to work reasonably well is to fill the groove in the hub into which the plastic sealing cap fits with water-resistant wheel-bearing grease. |
Thanks for the tip. I'll grease up the cog-side.
Someone else tried the electrical tape: https://cimg9.ibsrv.net/gimg/bikefor...6f5c88cd8d.png |
Since the hubs are compatible, it was a snap swapping the 8R31 for the C6001.
Thanks to its needle bearings, I confirm the latter runs better, especially the previously crappy 4th gear, even while still running its original Shimano grease. https://www.sheldonbrown.com/nexus8.shtml https://www.2rad.nrw/project/shimano...abe-demontage/ https://wanderingdanny.com/oxford/20...-8r36-redline/ https://cimg0.ibsrv.net/gimg/bikefor...72f14592f9.png -- Edit: Stats: On average, after giving the crank a one turn spin by hand with the Brompton (ie. 16" wheel) on a stand… - the 8R31 with the original Shimano grease stopped after about 5s - the 8R31 after being bathed in ATF oil would stop after about 10s - the C6001 with the original Shimano grease stops after about 15s. I guess the C6001 will spin a bit more the day I give it an ATF job. |
All times are GMT -6. The time now is 04:48 AM. |
Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.