single speed efficiency
 

I recently built up my first single speed (since my first grade BMX) as an in-town commuter/snow bike/project.

I was actually rather shocked by the feeling of efficiency and immediacy in pedaling. I had to get out my multi speed bike and put it in the same gear combo just to make sure I wasn't just imagining the difference. Has anyone figured out the mechanical advantage in having a straight chain line vs. the more convoluted path of a derailleur chain? I still reach for the shifter as a reflex now and then, but I suppose that it will soon pass.

i don't know about the physics behind it, but i do know that's a common thing. and damn cool, too.

welcome to the cult. Check out this PDF on the efficiency of fixed.

EDIT: This talks more about fixed than SS, but you may find it interesting nonetheless.

I found the efficiency of a singlespeed impressive, and the efficiency of a fixie about 10x more impressive than that, especially on hills.

ack. not the scleronomous gyrator crap again.
that argument is ********.

perhaps i will have to invest in a fixed rear wheel. any recomendations on a reasonably priced option?

not sure what the going price is, but check out ben's bikes. i've never had occasion to do business with them, but i hear they're good to work with and their prices aren't bad either.

oh yeah...and someone will definitely tell you to check out this page, too...

http://www.irocycles.com

or is it....

http://www.irocycle.com

either way, IRO will be much lauded here.

iro is closed right now for inventory and I don't think you can access any of the pages....

if you do buy a fixed gear rear wheel buy a fix/fix rather than a fix/free....because you can still thread on a singlespeed freewheel to the fix sides.... and then you'll be able to have two cogs on the rear if you decide that you like fixed gear.

If you replace a tensioner-less ss freewheel with a fixed cog, other things equal, you get absolutely no efficience improvement. Zero. Uphill, downhill, northern or southern hemisphere, wearing a clownsuit, whatever. The route of the chain is where it's at, and that's the same with fix and ss.

Found this thread through search... worth reviving.

The pdf linked above gives a very strong argument for why fixed is more efficient than SS... The cranks turn themselves at the top of the stroke where the rider can't put in as much power.

With that said, I'm thinking of removing the derailleurs and inner chain ring on an old 10 speed that shifts just fine.

I'm not that strong a rider, but my favorite gear is 48/18 (72"). I like climbing up 7% grades in 40/18 (60"), and the lowest gear on the bike is 40/22 (49"). I'm not really used to standing much, but the bike feels suited to it, and going up seated at 40-50 rpm is ok. How do you decide what gear ratio to use?
The straightest chain line would be 48/16. And I have other bikes, including a slightly slower one with STI shifting and wider gears, and rides where there are no climbs above 5% (72" would be ok), and rides where 10%+ climbs are very short.

From what I gather, getting rid of the deraillers will increase efficiency both because of weight savings (close to 24oz I guess) and because the chain doesn't go through extra pullies.
Can I easily switch between 2 close cogs on the back by just not seating the wheel as far back as possible?

End of debate. There are holes the size of the Hoover dam in the gyrator argument. It's so ******** it's not even funny, and so obviously false I don't feel like reading it again and refuting it point by point.

I couldn't concentrate on the rest of your post...

It's mean to trick the noobs like that.

any increase in efficiency could easily be tested with srm cranks and a power tap... I'm willing to bet there would be no significant difference.

one thing that's great about bf is that everyone that argues physics, obviously knows very little about it. hell, i don't know physics either, but i'm not getting my drawls in a bunch over it.

off-topic but: you're from western MA? where?

are you talking about whoever wrote that "paper." It may have been intended as a joke.

i'm talking about everyone.

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I started this thread ages ago, but I assume you are refering to me (?). I live in Amherst, MA.

It doesn;t take much physics to understand the how bike pedalling works. Anyway the main flaws in that paper are logical not due to the physics. The physics is just there to mask the logical flaws with big words.

There is no tricking here. SS/fixed is noticeably more efficient than geared.
The bet is on. Name the stakes, do the test and pay up.
If Sheldon's site was up, I could point you to his take on the issue, but you'll have to believe me as it is... or not.

(BTW, the basic flaw in the schleronomous crap is that it starts out from the (false, but that's irrelevant here) supposition that the fixed drivetrain revolves at an entirely even speed as the crank pushes your foot at every revolution, as opposed to freewheel (the author seems to think that people coast into every crank revolution... no comment). Then he tries to derive an energy gain from the even movement, which is absurd. Even if this supposition was correct, the cranks pushing your foot would obviously be an energy loss. Whatever other minute factor helps your pedaling, it would be smaller than that, so you're in negative territory. That's as much as I remember. Basically, every single step is laughably off base in that text.)

You get me both srm cranks and a powertap and I will happily do the test. I would be suprised if the drag of the rear derailer pulleys or the extra friction in the chain would be significant. Those are the only differences between the two drivetrains.

If I remember correctly the biggest flaw in the paper is that he says A causes B then conlcudes that B causes A.

There is one other difference: The chainline for a geared bike changes. If the cog and chainring are not coplanar, a (small) amount of the pedaling force goes to pulling the cog sideways.

I wouldn't expect to find more than a 1 or 2 % efficiency difference.

I was hoping that you would supply the tech stuff:D
Yeah, the pulleys and the winding route of the chain, plus the sometimes very crooked chainline are the only difference. But that's a lot, actually.

Here's a question, and I know nothing about physics::o on an SS freewheel the cranks are spun with x lbs. of pressure from your legs. with a fixed gear, they are being spun with x lbs of pressure from you legs plus the rear wheel is spinning them thru the drive train at x lbs generated by the inertia of your speed and rider/bike weight. Would'nt that mean, at a given speed, you would need less lbs of pressure from your legs on a fixed then a SS freewheel? the differnce being the energy transfered to the cranks via a fixed drive train? Does this make any sense?