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Thread: Belt drive. Why not?
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11-16-2016, 12:37 PM #51
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11-16-2016, 12:40 PM #52
High torque (relatively) is quite correct.
I've ridden a few belts and I'm convinced. I have a very old bike that is very close to falling apart and needs to be replaced. I like the new bikes. And yet I wait. I don't want to buy another bike with a chain.
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11-16-2016, 12:55 PM #53
Belt plus IGH seems like a good thing for a fatbike. I've had my RD/cassette get all gunked up with snow/slush and start skipping.
Also this is pretty sweet:
http://www.raleighusa.com/rxs
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11-16-2016, 01:18 PM #54
Internal gear hub comes at the cost of significant energy loss in all but the direct drive gear (11th gear on a Rohloff hub). The question is whether the energy loss per planetary gear transmission is setoff by the superior protection from weather and dust.
IGH bikes can also be awkwardly heavy in the rear, can be an issue when carrying your bike.
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11-16-2016, 01:31 PM #55
Total efficiency for the Rohloff is reported (quite believably, given typical planetary gear efficiencies) as 95-99% depending on which gear you're in. Doubt the Shimanos or the dual-shaft style Pinion does nearly as well, but if a dirty chain falls to 85-90% as some claim they're probably all fine for filth duty.
Weight in the rear hub is noticeable when riding. I got on a Rohloff-equipped bike at Outerbike and followed it immediately with one with the Pinion and even in a hardtail the light rear wheel with the Pinion mounted at the BB is very noticeable. I'm surprised Rohloff hasn't offered their internals in a casing for frame-mounting yet, because that seems like the best answer so far. (Still a bit heavy, but I'd take it.)
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11-16-2016, 01:38 PM #56
A chain would need to get so dirty to the point of very stiff links to lose that kind of efficiency. Don't get me wrong: Rohloff hub is remarkable engineering and would be a great choice for many. Also note that a Rohloff hub requires maintenance, which can be a bit trickier than lubing a chain, although needs to be done much less often.
Non-Rohloff IG hubs are indeed less efficient, some more than others.Last edited by Big Steve; 11-16-2016 at 01:56 PM.
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11-16-2016, 01:44 PM #57
How do the belt-driven bikes deal with replacing the belt? Splicing?
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11-16-2016, 02:15 PM #58
You open up the notch on your frame, take the belt off, and install a new one.
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11-16-2016, 02:30 PM #59
Have you ever seen a dirty chain tested for efficiency? I'm assuming that the low end of the range includes a mud-filled jockey wheel or two and horrible chain line at both ends, but I've actually seen claims as low as 80% for a badly maintained drive train. It's been a long time though, and I don't recall the source so the veracity is totally questionable. I'd be very interested in seeing an actual worst-case (or even average-case) scenario tested.
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11-16-2016, 04:19 PM #60
No, I haven't. What does efficiency mean in that context? Is the chain isolated or is it a test of overall efficiency of the drive train? If the former, how does the chain efficiency number relate to the overall efficiency of the drive train?
As you know "efficiency" is an ambiguous term that gets thrown around alot but can be measured in many ways, even on the same systems. I have ridden Rolhoff-equipped bikes and I cannot recall ever "feeling" that a dirty chain approached the "feeling" of drag of a Rohloff hub in the gears with the most drag (ETA except when I've had a derailleur drive train gets fouled with snow and ice, and I don't know whether or not belt drive would have solved that problem). Yeah, I know that's not scientific. But neither is comparing apples efficiency vs. oranges efficiency. And I can tell you with reasonable certainty that a sorta clean and sorta lubricated derailleur-equipped drive train is more efficient than a Rohloff drive train in everything but 11th gear.
And so, again, the question is whether the constant additional drag (in all but 11th gear) of a Rohloff hub is offset by the effects of dirt and weather on a derailleur drive train. Surely there are some circumstances where that is so. FTR, I have little MTB experience although I have ridden thousands of miles of dirt roads, e.g., from Missoula MT to Anchorage AK in 34 days, 31 of which were rainy. It would have been nice to have had a Rohloff hub for a few of those 34 days.
ETA: I acknowledge other advantages of IG hubs, e.g., the ability to shift while sitting still at a traffic light.
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11-16-2016, 05:10 PM #61
In an engineering or scientific context efficiency is defined as the ratio of power coming out of a system divided by the power going in. So unless it'smeasured wrong it's actually well defined, but with that said, I don't know how you could reliably separate chain drag from all other losses in a standard drive train. So to answer your question, I believe the only good test is drive train vs. drive train.
With respect, I can't believe anyone can actually feel the difference between the efficiencies in different gears through your legs because your legs only feel torque and speed on the input side. It's easy, with training, to notice a lot about the input side, but feeling the resistance you're overcoming (wind, rolling, slope up/down) with adequate precision is a lot harder. Actually comparing efficiencies requires feeling both sides and comparing from gear to gear, so the machines tend to come out for that kind of stuff. Of course, with the machines come the question of whether the real world has been lost, too.
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11-16-2016, 05:19 PM #62
I had a Truvativ Hammerschmidt Crankset for a while - two internally shifted gears that used a planetary arrangement. Supposedly those things were between 90-95% efficient, but the extra drag was super noticeable. It was far worse than any dirty chain I've encountered (not counting old ones that were rusted solid). And that efficiency loss was only in the "big" chainring - the climbing gear was direct drive. I ended up selling it because the extra drag was so annoying.
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11-16-2016, 05:38 PM #63
A 10% drag I can see noticing, for sure (and those would have to be some seriously crappy gears compared to Rohloff's, but that definitely happens). And I'm speculating a bit about how bad a Rohloff might get--obviously if a bearing starts to drag a little that would change things. I'm just saying a 2% efficiency change from one gear to the next is less noticeable than the difference between a 13% upshift and a 13.5% step, for example.
Eta: point being: efficiency can get lost in step differences, especially since they're not quite even.
To walk that back yet a step further, I found a ratio in the Pinion that I was less pleased with than the others. I attributed that to shift performance and sound change, but it's possible that with more time on it I could hate that gear in earnest. Hard to say.
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11-16-2016, 06:50 PM #64
Belt drive. Why not?
Well maybe I'm the faggot America
I'm not a part of a redneck agenda
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11-16-2016, 07:01 PM #65
FTR, I rode Rohloff-equipped and derailleur-equipped bicycles back to back to back to back (2 x 2 laps) on the same (hilly) course and the latter was measurably faster for me and for the other guy participating in this rough experiment. (He owned both bikes.) We timed each other. The bicycles were not otherwise identical, although they were equipped similarly, e.g., tires, tire pressure, seat height, crank length. No, I wasn't wearing a HR monitor, so it wasn't scientific, but I'm pretty certain that the derailleur-equipped bicycles were indeed faster. FTR, we had a few beers.
As you know, drive train drag (and other drag, e.g., brake drag, binding wheel bearings) can be noticed with a bike in a repair stand. When I was a shop rat I diagnosed lots of problems by noting drag while the bike was on a bike stand. Anybody would notice the drag of a Rolhoff hub in the least efficient gears on a bicycle stand, just as they would notice the drag associated with a dirty chain. I am not suggesting that one could make any meaningful measurements that way.
I agree that one might not notice 2% drive train efficiency difference by feel while riding, but it sure seems that the difference in drag between a clean well-lubed derailleur transmission and the least efficient Rohloff gears is more than 2%. (ETA: The article I linked in ETA2 below confirms this.)
ETA: The final sentence above assumes a new Rohloff hub. I've read and heard that the seals loosen up after a few thousand miles and as a result a well-used hub might have less drag.
ETA2: IHPVA Journal: The mechanical efficiency of bicycle derailleur and hub-gear transmissionsLast edited by Big Steve; 11-16-2016 at 07:26 PM.
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11-16-2016, 11:49 PM #66
That article is interesting, and some of the observations look useful, but as they noted, it leaves more questions than answers. I don't trust their specific measurements very far, for several reasons, but I'm not sure anyone here is interested in diving into the weeds. Suffice it to say, the data they show in their final table does not show a greater than 2% difference between the Shimano 27-speed and the Rohloff, if the data is taken at face value. But they did use a very well-oiled chain, which is really the problem: how to compare a nice clean belt with a chain that started out wet and collected gunk? Also, how would a 1x11 (or 12) compare in its extreme gears--especially since 15 years on we're using 10 or 11 as the small cog instead of 12?
I guess I'm willing to assume that an IGH would be more efficient for a while if, like a derailleur system, it had no contact seals. But the seals are worth it so they seal these systems because they can.
This is the answer:
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11-17-2016, 12:49 PM #67
That's the answer to a different question. That plug has the belt on his W-side bike confirms my statement that the Rohloff hub -- in this case together with belt drive -- loss of efficiency via friction of many spinning gears is setoff by environmental factors, in this case muddy W-of-crest conditions.
Huh? 3rd gear: 92.8 - 87.8 = 5.0. 7th gear: 92.6 - 86.1 = 6.5. And, no, I'm not cherry picking because the issue is the loss of efficiency with Rohloff hub's least efficient gears (3, 5, 7, 12, 14), i.e., when the most IGH gears are spinning resulting in more loss of energy via friction.
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11-17-2016, 02:00 PM #68
I'm sure that feels like it's not cherry picking, but of course 3rd, 7th etc are not the same in a sequential 14 speed vs. a 3x9, so there's no reason to compare those. The relevant comparison is between least efficient gears on each system, since both systems will see use in those gears. The fact that they occur at different ratios isn't meaningful to any rider I know. As such, note the 89.5, 89.4 and 90.0--to say nothing of 86.9% in 24th (a currently common 32x12) on the Shimano. I will admit to shifting to the big ring for a sense of higher efficiency on a 3x9, but how many people would keep the big ring just for that purpose? (Although a 7% gain certainly starts to justify it.)
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10-11-2017, 09:22 PM #69
Another year of absolutely no maintenance on the belt. The bike is just so fun to ride hard and put away wet and not care about it.
Well maybe I'm the faggot America
I'm not a part of a redneck agenda
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10-12-2017, 09:23 AM #70
skibee is on 5+ years with her belt drive spot rocker SS. I have had to do exactly nothing to it
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10-12-2017, 11:10 AM #71
If belt drives were so great, they would be all over the racing circuit, because I can't actually see mechanical reasons in favor of them, unless these carbon fiber belts(?) have a much better transfer of energy, and I can't really see that as being the case. Less weight would be a plus, though.
Now belt drives for commuter bikes, that I would love to see more of. I'm sick and tired of ruining my good street pants with chain grease when I forget to wear a right leg band. Plus you have too tuck your pants just right, or it screws up the crease in slacks. Yes...if Iceman skis in jeans, I sometimes ride bikes in slacks!!
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10-12-2017, 01:05 PM #72
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10-12-2017, 02:26 PM #73
What mntlion said, plus, you really can only compare to other SS bikes, and igh bikes. In that case, the percentages are swinging in belt’s favor, (slowly). One cyclocross racer I follow says that if it’s a hilly course and it’s raining his belt drive is way faster.
Well maybe I'm the faggot America
I'm not a part of a redneck agenda
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10-12-2017, 03:25 PM #74
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10-12-2017, 09:40 PM #75
I think they would work great for a simple single speed stainless steel folding bike though. No rust! And no grease to muss up your sail covers. And yes, they actually make a stainless steel folding bike for boats. It folds into a leather monogrammed suitcase and costs about a gazillion dollars.....but STILL has a greasy chain.
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