Author Topic: Four gears in hub.  (Read 22423 times)

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Offline Westinghouse

Re: Four gears in hub.
« Reply #15 on: March 01, 2009, 07:39:57 am »
That  tells me something about those cheap wheels I have always used on long loaded tours. Usually I would pay about $30.00-$35.00 for wheels. I have not had problems with spokes in front wheels. With these cheaper back wheels on a loaded tour I could go about 3,800 miles before breaking a rear spoke. I got only about 1,600 miles on another before breaking the first spoke. If I use a cheap back wheel for one long cross country tour, it might not break a spoke at all. Leave the wheel stored a while and start off on another long tour, it starts breaking spokes early in the trip, and may keep breaking in the same spoke position over and over again. You must be getting much better built wheels. I see if I want to eliminate the problem I will have to buy more expensive equipment.

As for those internally geared hubs, they can be extremely expensive and way more than I could see myself paying.
« Last Edit: March 01, 2009, 08:05:35 am by Westinghouse »

Offline whittierider

Re: Four gears in hub.
« Reply #16 on: March 01, 2009, 11:27:04 am »

Quote
You must be getting much better built wheels. I see if I want to eliminate the problem I will have to buy more expensive equipment.

More than $35, definitely; but not particularly more than other mid-range alloy wheels.  The wheels we've bought from Peter White with Ultegra hubs and the Velocity Aerohead rims (using O/C on the back) were about $400 per pair.

As for the tandem wheels, 145 and 160mm are the two rear dropout spacing standards now.  Our tandem has 145 and there's still some dish to the wheel, but it has been trouble-free for 10,000 miles.  Santana has some 16-spoke tandem wheels that have an excellent reliability record, so you can see there's a lot more to wheel strength and reliability than just the number of spokes.

Offline TCS

Re: Four gears in hub.
« Reply #17 on: March 02, 2009, 08:36:25 am »
Science on the efficiency of chain drives begins on page 3 of this publication:

http://www.ihpva.org/HParchive/PDF/hp50-2000.pdf

Measured efficiencies of several derailleur and hub gear drivetrains begins on page 3 of this publication:

http://www.ihpva.org/HParchive/PDF/hp52-2001.pdf

Human Power isn't just some bicycle magazine; it's a respected, peer reviewed scientific journal.  These researchers/writers are considered to be world leaders in the field.

tcs
"My name is Pither.  I am at present on a cycling tour of the North Cornwall area taking in Bude and..."

Offline TCS

Re: Four gears in hub.
« Reply #18 on: March 02, 2009, 08:39:40 am »
The range of 84% to 98% is huge.  It is not a trivial difference.

That is true, and it's amazing that those efficiencies can be exhibited by different gear ratios in a hub or in a derailleur drivetrain on a single bicycle.

tcs
"My name is Pither.  I am at present on a cycling tour of the North Cornwall area taking in Bude and..."

Offline TCS

Re: Four gears in hub.
« Reply #19 on: March 02, 2009, 09:02:49 am »
If I can actually feel that negative difference in efficiency, there is  difference enough to consider not using the wheel.

I'm of the opinion that while one might feel drivetrain vibration or hear drivetrain noise, a rider can not "feel" efficiency. 

A 39T chainwheel and an 11T cog give about the same ratio as a 52/15 - but the 52/15 is up to 10% more efficient!  The science of this was know even back in the 1890s, but because efficiency can't be "felt" by the rider, this knowlege remains rare among riders.  Indeed, reviewing nearly 50 years of popular cycling journals, I didn't find any recomendations to use larger, more efficient tooth counts - but I did find a number of recomendations to use smaller tooth counts to save a few ounces of weight!

For a practical application, consider cycle racer Lance Armstrong.  Many commentators noted his average crank rpm was higher than nearly all of his competitors.  If his competition were using, say 53/11 ratios and turning 90rpm, he would be in his 53/13 and turning 106rpm, operating a drivetrain that was more efficient by a few percent, and...winning.

Best,
tcs
"My name is Pither.  I am at present on a cycling tour of the North Cornwall area taking in Bude and..."

Offline biker_james

Re: Four gears in hub.
« Reply #20 on: March 03, 2009, 07:38:06 am »
The links do lead to some intersting reading on the subject of efficiency. I am a little skeptical about some of the numbers, but have to say that I am not a scientist to dispute them either. I would also suspect that with the redesigns done of cycling equipment, and gear tooth shapes that the numbers may no longer be totally correct. I am not certain that I am rushing out to change my drivetrain on my bike on the hopes of massive gains in efficiency. It does seem surprising that they are showing higher losses at lower power, which certainly seems rather backwards.
The Lance Armstrong scenario you propose is a little too simplifies though. Perhaps the biggest factor on cadence and gear choice has to do wtih the physiology and training of the cyclist. What may be an efficient cadence for one rider may not be as good for another rider due to their body design, musculature, and fitness. I also take it form their cahrts that perhaps the most efficient is a single speed, or maybe fixed gear bike, which have the added benefit of fewer moving parts and lower weight also. But they wouldn't be much use touring in the Rockies with 50 pounds of gear.
I will definitely be re-reading these articles though. Good food for thought.

Offline Westinghouse

Re: Four gears in hub.
« Reply #21 on: March 03, 2009, 08:03:56 am »
You all have much more knowledge on equipment, and on the technical aspects of cycling than I have. That is why my information to newbies on gear is always general. The most I ever got out of a $30.00 rear wheel before breaking a spoke was about 3,800 miles. After a spoke breaks, they keep breaking. However, I read Whittierider's suggestion on page one of this thread for the kind of wheels to buy. In fact, I did have a set of wheels just like that one time. I was living and working in Beijing, China. I went to a small, hole in the wall bike store. I saw the wheels on a bike but I didn't want the bike. I made a deal with the shop owner. He sold me both wheels for seven dollars each, but that was China. I also got two GoreTex jackets, one of which was top of the line, for a total of seventy dollars; like I said, that was China. I used those wheels on long tour with no problem. However, they did have a chink in their armor. The steel spokes went into steel fittings in the alloy wheels. After a tour of the outer banks and the east coast the salt did its work, corroded the spokes, and the fittings. I lost three spokes in the rear wheel, and five in the front from corrosion, but the wheels stayed true. If they had been all alloy and stainless, I would probably still be using them today. What cost me $14.00 in China might have cost me $150.00 in the USA.

The thirty dollar wheels I use are not good on the back of the bike, but I have not had a broken spoke on a front thirty dollar wheel even on very long tours and rough roads. But of course, after tour I must buy new wheels. I cannot use them over and over again touring like others can on better quality wheels.


Offline DaveB

Re: Four gears in hub.
« Reply #22 on: March 09, 2009, 07:45:20 pm »
The most I ever got out of a $30.00 rear wheel before breaking a spoke was about 3,800 miles. After a spoke breaks, they keep breaking.....

The thirty dollar wheels I use are not good on the back of the bike, but I have not had a broken spoke on a front thirty dollar wheel even on very long tours and rough roads. But of course, after tour I must buy new wheels. I cannot use them over and over again touring like others can on better quality wheels.
Well, I typically get 30,000 or more miles out of a wheel built with Shimano 105 or Ultegra or Campy chorus hubs, DT or Wheelsmith spokes and Mavic CXp-33 rims.  The rear wheel costs about $160 so, since I get nearly 10X the number of miles, my per mile cost is just over half of your $30 wheels and I NEVER break a spoke, the rims eventually crack from brake wear.

There is a saying that; "only a rich man can afford cheap tools."  You must be rich.

Offline whittierider

Re: Four gears in hub.
« Reply #23 on: March 09, 2009, 09:46:36 pm »
Quote
Science on the efficiency of chain drives begins on page 3 of this publication:

http://www.ihpva.org/HParchive/PDF/hp50-2000.pdf

Measured efficiencies of several derailleur and hub gear drivetrains begins on page 3 of this publication:

http://www.ihpva.org/HParchive/PDF/hp52-2001.pdf

I'm glad to see a lot more data than what was in the tiny Bicycling article a few years ago.  This is so much more enlightening.

The second one above was not my favorite of the two articles, but it still shows a lot of work went into the tests.  They mentioned more than once that they didn't have time to take very complete data, and it shows.  It would have been easy to use the computer for not just data acquisition but also for control, to vary the load, the speeds, and the gears, so it could take more complete data in far less time.  I do this kind of thing frequently in my work, although with electronics instead of mechanical.

I wish they had connected the ergometer wheel directly to the hub instead of going through another chain drive which had, as they admitted, an unknown amount of loss.  They did a preliminary test, but not at all the wheel speeds and torques involved in the subsequent drive tests.  Both this report and the other one say that the speed and force affects the efficiency significantly.  The unknown quantity still allowed relative comparison of drive types to each other, but the true efficiency of a given system could only be estimated without knowing that missing variable.

They used only 75rpm, which is unrealistically low for riders who will be most interested in this material, ie, the ones who want to go faster.  As for the power levels, I only dip to the 80W level if I'm riding with someone who's slow (like my wife).  I will be most interested in the efficiency numbers when I'm producing 150-900W.  Interestingly, both types of systems get more efficient at higher wattages; but they assumed that the rider of a geared hub won't often produce more than 150W, so they didn't test the derailleur systems at the levels many of us are interested in either.

They tested the derailleur system, at least the Shimano 27-speed, apparently with an Ultegra rear derailleur (or its MTB equivalent), which has those pulley dust seals that quickly get stiff and don't want to turn.  (The top one is especially bad.)  After trying various kinds of lubes, I went to the ball-bearing type to save several watts.  Cheaper Shimano derailleurs without those dust seals are better in that respect.  Then they made the mistake of sorting gears instead of leaving them as 1-9 being granny ring, 10-18 being middle ring, and 19-27 being big ring.  It took more time to figure out which combination they're really talking about for a particular result, and whether it was even one that a skilled cyclist would avoid (e.g. the tiny ring and the smallest cogs).  Few road riders will be using a 22-32-42 crankset either.  30-39-52 or 30-42-52 is the common set, and will make for better efficiencies.

I was a little surprised that the geared-hub systems generally came out only a couple of percentage points worse than the derailleur systems.  I'm sure the spread would have been greater with better pulleys giving a greater advantage to the derailleur systems.  The only non-Shimano-27 derailleur systems they tried were the Browning, which no one here would consider serious contenders for someone interested in performance and efficiency.  It would have been so much more appropriate to try typical road set-ups from Shimano, SRAM, and Campy.  I don't think it will ever be possible for a geared-hub system's efficiency to meet or exceed that of the derailleur system, since the geared hub does not get rid of the chain's losses.  The geared hubs also give bigger step sizes between gears, which will make the human engine less efficient than he would be with the derailleur system and our common 12-25 cassettes.

Quote
http://www.ihpva.org/HParchive/PDF/hp50-2000.pdf

Excellent article, although it does not cover internally geared hubs at all.  I was a little surprised at how little a bad chain line affected the efficiency (even though it is definitely harder on the equipment).  It was interesting to note also that the type of lube had almost no effect on efficiency either.  They did say at the end that friction only accounts for a small part of the loss-- which is very puzzling.  Where is the rest going?  Perhaps the chain pounding the teeth as it lands on them to engage?  (That would be constant for a given speed, correlating with the fact that efficiency increased as power increased.)  This seems to be the only hole in this particular article-- the fact that they did not look into this further after raising the question.

Offline Westinghouse

Re: Four gears in hub.
« Reply #24 on: March 10, 2009, 08:46:27 am »
From my own non-technical point of view, if I can get an undished rear wheel and use the deraileur system, all I need is a better quality rear wheel, and my transcontinental touring problems would be greatly reduced. Considering the extremely high costs of some of the internally geared hubs, and the loss of pedaling efficiency, I think I would go with a cheap reliable front wheel, and a better quality undished rear wheel.
« Last Edit: March 11, 2009, 02:57:27 am by Westinghouse »