tag:blogger.com,1999:blog-36151678.post11428883155424265..comments2024-03-26T04:02:22.355-07:00Comments on Waltworks Bicycles: Brief rant, brief recipeWalthttp://www.blogger.com/profile/09156620599767391579noreply@blogger.comBlogger9125tag:blogger.com,1999:blog-36151678.post-53357092441075793572012-12-10T21:27:12.944-08:002012-12-10T21:27:12.944-08:00I think there are scientific justifications for bo...I think there are scientific justifications for both perspectives. I think we're somewhat close to the situation of a forced harmonic oscillator, where the forcing frequency (pedaling) is much lower than the natural (resonant) frequency of the frame (ie if you flex the frame it will vibrate at a much much higher frequency than the 2-3 Hz at which you can pedal in a sprint). <a href="http://www.acs.psu.edu/drussell/Demos/SHO/force1.gif" rel="nofollow">Here</a>'s what happens in that circumstance: after a somewhat chaotic looking start to the sprint (frame moving out of sync with rider's pedaling), the frame settles down to oscillate at the forcing frequency with stable amplitude. The amplitude of the oscillation is lower for a stiffer frame, and the energy stored in the oscillations is then lower also (proportional to force * displacement). But the power being absorbed is zero in both cases because there is no damping in the system. The questions then become, how damped are the actual systems, and how significant is the energy that became stored in the frame oscillations rather than in forward movement? My sense is that with a highly elastic frame material like steel or titanium, the damping is very low and can be ignored (so frame stiffness doesn't matter once you are up to speed and the oscillations become steady). But the less-stiff frame will have an increased duration and amplitude of the initial out-of-sync response to the start of a new effort (while the oscillation energy is being stored)... I'm guessing this is what leads to a stiffer frame "feeling" faster/better when you first launch your sprint.DanHnoreply@blogger.comtag:blogger.com,1999:blog-36151678.post-77223210740296625892012-12-06T21:45:06.548-08:002012-12-06T21:45:06.548-08:00My goodness, how quickly people have forgotten the...My goodness, how quickly people have forgotten the Alan and Vitus frames that many a race were won upon...and those early titanium frames where a strong rider could get both chainstays to rub on the tire.<br /><br />There's a force orthagonal to the drivetrain generated by pedal forces. It's inescapable. The force is there no matter if the frame is made of out paper-mache or reinforced concrete. And having the frame bend or not bend doesn't make any difference at all: there's no way that force can be recovered and put to use moving you forwards, because it's acting at right angles to the drivetrain.<br /><br />Back when I sold bikes, it was easy to get someone onto a Cannondale or a Klein: send 'em out into the parking lot and ask 'em to notice how the bike just squirted forwards when they mashed the pedals. The bikes sure <i>feel</i> different. But the stiffer frame isn't really faster, and it's usually a damn sight less comfortable, too.<br /><br />Now, you can get too noodly, and things like ghost shifting and the chain falling off start to happen. But if the power losses were as high as people like to think they are, a flexy steel frame would be hot to the touch at the top of a big climb. They're not, so therefore they're not absorbing power.BigHank53noreply@blogger.comtag:blogger.com,1999:blog-36151678.post-5840177733189038542012-12-06T16:46:35.147-08:002012-12-06T16:46:35.147-08:00I disagree too, I'd brush up on your physics. ...I disagree too, I'd brush up on your physics. Downward force on the pedal is going into twisting the frame instead of driving the sprocket.Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-36151678.post-44385421825929209872012-12-06T07:04:08.236-08:002012-12-06T07:04:08.236-08:00Stiffer not better--she said, never. Stiffer not better--she said, never. Lancehttps://www.blogger.com/profile/07401362436995139246noreply@blogger.comtag:blogger.com,1999:blog-36151678.post-18111289286938539992012-12-05T19:07:25.558-08:002012-12-05T19:07:25.558-08:00thanks for the recipe professa' now just recom...thanks for the recipe professa' now just recommend me some books!<br /><br />maybe the chicken will soothe my aching joints. just too much stiffness. ;)<br />jshttps://www.blogger.com/profile/10319654747959122637noreply@blogger.comtag:blogger.com,1999:blog-36151678.post-41727447890089145342012-12-05T14:49:28.439-08:002012-12-05T14:49:28.439-08:00I suspect you're both partially wrong and part...I suspect you're both partially wrong and partially right. (Not Mike, that is, I'm sure the peanut sauce is wonderful) My guess is that most people have a tendency to pedal sideways a bit. Having a rigid frame helps keep you pedaling in the right plane. Human bodies are complicated and really hard to model.<br /><br />To Walt's point, you can be exerting yourself and doing no work (the stated physics definition of work) -- see isometric exercises. But I think John has a point, too, as I attempted to explain in the previous paragraph.Feldyhttps://www.blogger.com/profile/09656849385504906513noreply@blogger.comtag:blogger.com,1999:blog-36151678.post-39099252095541994682012-12-04T21:22:18.633-08:002012-12-04T21:22:18.633-08:00Stiff feels good! Ha!
Super excited to make some...Stiff feels good! Ha!<br /><br />Super excited to make some Peanut sauce! Thanksmikehttps://www.blogger.com/profile/07924576541839331555noreply@blogger.comtag:blogger.com,1999:blog-36151678.post-73273101775822444132012-12-04T14:22:01.702-08:002012-12-04T14:22:01.702-08:00Again, vectors. If you've got a lever doing th...Again, vectors. If you've got a lever doing the work to push sideways, that makes no difference. You are pushing sideways, and having the frame resist that force does nothing to propel you forward. <br /><br />So you are sort of half right - because your pedal is off to the side, you're generating some lateral force. But that still doesn't mean that a stiffer frame can somehow take that lateral force and turn it into forward movement. What you see at the BB is the result of you pushing - the energy is gone either way.<br /><br /><br /><br />Walthttps://www.blogger.com/profile/09156620599767391579noreply@blogger.comtag:blogger.com,1999:blog-36151678.post-63216366864730211992012-12-04T14:16:30.999-08:002012-12-04T14:16:30.999-08:00Even if your legs are theoretically pushing perfec...Even if your legs are theoretically pushing perfect circles with only downward vertical forces applied to your pedals there is still a lever arm that is roughly equal to the distance from each pedal to the lateral center of your frame. This creates a moment in the lateral plane that will cause deflection in a bike frame(i.e. you don't need to push sideways to create lateral frame flex). W=f*d , A force does work when it results in movement. P=W/t , Power is equal to the change in work divided by the change in time. Unnecessary frame movement=unnecessary use of power. Love ya Walt, but I disagree. You agree that super flexy is not a good thing, what is your reason? Is there a benefit to lateral movement of a bike frame? Johnnoreply@blogger.com