Comments on: Project SSR, Part Two: The Science of Singlespeeds

By: Lath_Carlson

Lath_Carlson — Thu, 19 Jun 2008 13:10:42 +0000

That’s a great idea for a study, I don’t believe it’s been done yet. Although because of the very small differences it is probably more realistic to do it with a constant torque motor drive suppling the power and a load cell at the cassette (Powertap) to measure differences in delivered power. Any engineering grad students out there? High schoolers needing a science project?

The closest thing I’ve seen is a study that found that:
“Chain drive efficiency has been studied to understand energy loss mechanisms in bicycle drive trains, primarily for derailleur-type systems. An analytical study of frictional energy loss mechanisms for chain drives is given along with a series of experimental measurements of chain drive efficiency under a range of power, speed and lubrication conditions. Measurements of mechanical efficiency are compared to infrared measurements indicating that frictional losses cannot account for the observed variations in efficiency. The results of this study indicate that chain tension and sprocket size primarily affect efficiency and that non-thermal loss mechanisms dominate overall chain drive efficiency.”
From: Effects of Frictional Loss on Bicycle Chain Drive Efficiency
Journal of Mechanical Design — December 2001 — Volume 123, Issue 4, pp. 598-605

By: Garden Gnome

Garden Gnome — Thu, 19 Jun 2008 06:33:57 +0000

I thought of an interesting experiment around drivetrain efficiency. I hypothesize that a large proportion of efficiency loss can be attributed to chain line. A straight chainline being the most efficient of course, but how much does being 1mm, 2mm etc affect it. I came up with this theory based on chain wear due to cross chaining (poor chainline.)
The experiment i have in mind to prove/disprove this theory involves a powermeter type cassette hub, a trainer, a derailleur and a bike with horizontal drop outs.
Step 1. Set the bike up an approriate gear (i.e; 70″) the actual gear needs to be the same throughout the experiment but the experiment can be repeated with various gear combinations to see if perhaps a higher gear ratio is more affected by chainline than a lower gear ratio. We are simply looking at the effects of chainline. Set the chainline using a single gear with spacers on either side and a derailleur lined up vertically with the gear. this is the ‘Zero’
Step 2. Pedal the bike at constant speed or power. Record observed power or speed.
Step 3. Move the gear one spacer in or out (+/- 1). Realign deraileur and repeat step 2.
Step 4. Repeat Step 3 until the last gear is in the last position and then repeat step 3 in the opposite direction from the zero position.
Step 5. Remove derailleur and tension chain by shortening chain and moving the wheel. Try to keep the chain stay length as close as possible to that used in steps 1-4.
Step 6. Repeat Step 2.
Step 7. Move the gear one spacer in or out (+/- 1). Realign deraileur and repeat step 2.
Step 8. Repeat Step 3 until the last gear is in the last position and then repeat step 3 in the opposite direction from the zero position.

Now if we graph the results of power or speed while the other is held constant versus gear position (+/-1, +/-2 etc) we shoud see the effects of chainline efficiency for both single speed and geared set ups and what effect a derailleur has on efficiency and if it that effect varies with chain line.
Hope this interests somebody. I don’t have a power meter of any type so I am unable to do the experiment.

By: scott

scott — Wed, 18 Jun 2008 05:21:12 +0000

When discussing mechanical technical issues it is easy to just approach things from an engineering standpoint , IE “fewer parts equals greater efficiency “. However if the vehicle in question is human powered it is valuable to consider the psycological aspects and advantages to the system in question .
Riding a singlespeed trains you to work harder . No bailout gear means you have to pedal harder and or stand up more of the time , period . Everybody knows that standing up uses more energy , so you end up riding seated longer than you would have before . Then you stand on the pedals . While lacking ultimate efficiency , standing does crank up your cardio workout and still provides a benefit you will miss when you just shift another gear .
Riding a singlespeed gives you a psycological advantage over your competitors . They look at your bike and they KNOW your bike weighs 1 or 2 or 3 pounds less than theirs . They think that if you are wiling to ride the same course as them with only one gear that you must be tough . They know that if they snap a shifter cable or smash their derailler on a rock , they are toast and you will just motor on by .
The thing I like most about riding a singlespeed is it teaches you new skills . I started riding a singlespeed when I was 46 years old ( Im 50now ). I was burning out on riding – commuting , trail riding , I wasnt progressing in my fitness any more . When you have a job and a family there is only so much time and motivation in a day , you look for the next advantage . Since I cant afford a titanium anything , I downsized my drivetrain . Within a year , I felt 10% stronger than before . I spent less time wrenching than before . And people notice and make positve comments about your riding just because you left your gears at home . The best part is that now when I ride my geared bike I have skills and fitness I never would have developed without my singlespeed . And I can ride uphill AND downhill 2 or 3 gears higher than I did before .
SO , do you want to scrape together more money for some carbon fiber crap or doyou want to build a bigger motor ?

By: yooperlegs

yooperlegs — Thu, 12 Jun 2008 03:34:59 +0000

Recently i was coming back from a quick blast with my road bike and just glanced at this “totally cool” wannabe hipster girl riding down the sidewalk.She glared at me (I imagine-i was going up a hill,she wasn’t pedaling),briefly.
I imagined my bike wasn’t “cool enough” and i probably didn’t “get it”.I think “fixies” are getting like that.I will probably re-build my ‘98 Stumpjumper single ’cause I want to ride it without making it something that would lack against my other stuff.I love the frame too.It’s that or mount it on a wall.I shift often and go thru gears fast.No way you could hold my wheel.Shouldn’t be “too cool” and mis-represent data to support what we all love.

By: Lath_Carlson

Lath_Carlson — Thu, 12 Jun 2008 01:32:34 +0000

AntEater, well said! Your experience just about mirrors my own, which is what led me to starting writing about this. All of the points you mention we will be taking up.

Fire Horse, I agree with you regarding MTBR type flame wars, if only some of those people would ride as much as they post. So far the discussion here has been more insightful, just what I would expect from the readers of the Rag. My plan here is to start with the “scientific” and theoretical and move on to real world testing. I agree with most of what you bring up regarding this type of research, but it’s a good place to start the conversation at least. Try not to get too upset by my next post! Thanks for your comments regarding the reason for derailleurs, I heard one from an old tour rider that they were only good for riders over 45.

By: fire horse

fire horse — Wed, 11 Jun 2008 15:30:19 +0000

Lath_C, god bless ya. You are much, much more of a patient man then I ever will be. The bummer about posting messages is that not every one has the same amount of knowledge, experience, or objectivity about a matter, especially cycling. This is why I don’t even…bother with Craigs List Discussions or mtbr.com any more.

Some folks have their biases and no matter of convincing or “scientific” evidence will change their opinion weather it be the advantages of 29ers or singlespeeds. Look at all the anti-29er and anti-SS articles in that rag MTB Action. But still the market keeps growing and is here to stay in both sectors. They called it a fad but more people and companies are becoming and staying believers.

As for “scientific” evidence, studies can be just as wacked out as some of the uninformed or emotional opinions on here. For the uninitiated, so called “scientific” studies are with their flaws as well. Why, you involve people. Common flaws:
-vetting the peer review process: the opinion or unpaid, anonymous, and unaccountable individuals whose opinions are kept confidential making it impossible to know the parameters of the reviews.

-research articles are often…either contradicted, exaggerated, or seriously misquoted.

-reviewers are usually not allowed to contact the researchers directly to ask questions, and they do not try to replicate the research..wtf?

-granted, the system has often had successes but, peer review also lacks consistent standards.

-procedures vary among the world’s 10,000 or so journals. A peer reviewer often spends about four hours reviewing research that may have taken months or years to complete.

I could go on ad nauseum but I’ll spare us all. This brings us back to plain ol’ tired and true…common sense folks. The most elegant, reliable, and efficient designs are the most simple.

The more factors/processes involved in a mechanical process the more opportunity for friction, resistance, damage, reduced reliability, increased maintenance, increased cost, etc.

Addressing “Why was the derailleur created?” it was to make the cycling experience more accessible to masses which translates into more sales. The old timers, even on the Tour de France, originally rode fixed gears. This obviously wouldn’t appeal to your weekend warrior type. So enter the human factor.

You can either make the machine easier to ride, to do a particular task (ie ride over a mountain range) and thus appeal to more people. Or you can….evolve the rider. This transformation however involves sweat, pain, will power, and don’t say it…change.

Anyway Henry Sturmy (developer of the Sturmy-Archer hub) said it best “The only mechanically correct place for a gear in a pedal cycle is the hub …”.