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#11
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Not your typical tires
Tim McNamara wrote:
I think it is believed to be a spring similar to the belief that the curl in fork blades are springs. There has been some published data measuring vertical flex of bicycle fork blades under load. This flex was measured to be greater in forks with larger offset and a lower, tighter curl at the hub end; also, naturally enough, smaller diameter fork blades showed more flex. The magnitude was small, maybe 1/4" at most. Whether it's *useful* is a different story; the authors of the article believed it was but I can't say that I was convinced. For one thing, the load was static with weights applied to the front of the bike. I think static loads are appropriate for such measurements. As I mentioned in another thread, speed of application of forces is immaterial for structural metals. No doubt forks flex but not enough to constitute a spring, certainly not as much as the pneumatic tire furnishes. Most of the flex in forks takes place in the steertube that generally has a lower bending stiffness than the two fork blades it supports and whose bending load is pivoted about the lower head bearing. This also causes fretting damage to the lower and upper head bearing. Time's a little tight this morning, I'll dig up the article and post more specifics. I'm curious what the goal of this study was. Jobst Brandt |
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#13
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Not your typical tires
Carl Sundquist wrote:
Ignore the oval chain ring: http://tinyurl.com/66ztbn Look closely at the front tire at 1 & 7 o'clock. Look _very_ closely at the rear tire at 1 & 3 o'clock. Aren't you glad that your choices are limited to tubulars and clinchers? Solid non-pneumatic rubber tires are all they had for high wheelers and that drifted into the safety bicycle, this one apparently by Iver Johnson. I had a later IJ that had triangular taper BB and steel cranks. Realizing that the torsional strength of a shaft is roughly that of the largest inscribed circular shaft, a triangle doesn't leave much and with steel cranks had a poor retaining bolt to boot. Is that not a valve at 7 o'clock on the front wheel? I think that is where a valve wold go for a pneumatic tire, but these may be tire anchor screws to keep the solid tire from walking around the wheel and dismounting itself. I can't see any detail in the large gap in these tires to see their cross section but it seems to be mostly solid rubber. On another note, what was the benefit of the serpentine seatpost? I think it is believed to be a spring similar to the belief that the curl in fork blades are springs. Both tire valves are visible if you look closely. The rear valve, at 3 o'clock, is almost obscured by the chain stays. Here's the original page of photos: http://tinyurl.com/66ztbn You can see the valve caps on both valves. Here they are, cropped from three photos and enlarged: http://i33.tinypic.com/se885v.jpg The holes for the valves are at the riveted rim joint. Someone may have taken the old pneumatic tires and tubes off, leaving the valves in place, and installed "cushion" tires as described in the auction text. Cushion tires were hollow, but not inflatable, so they flexed and wore rapidly. That was my suspicion, considering the non-pneumatic tires. I'd love to see the actual bike and find out exactly what's going on. *** As for the odd seat post, that was just one early shape. It looks strange to us, but it was cheap, easy, and simple to bend a solid rod like that: http://www.auctionflex.com/auctionim..._2BX0U29PG.jpg http://www.auctionflex.com/auctionim..._2BX0U2N4Y.jpg It's very easy to get at the clamping bolt under the seat and then slide the seat back and forth on its long level section to suit the rider. Thanks for the details. I find these bicycle interesting because they often reveal that the ancients were up against difficult design problems and found solutions that are often missing today. Jobst Brandt |
#14
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Not your typical tires
On 02 Nov 2008 20:27:05 GMT, wrote:
Carl Sundquist wrote: Ignore the oval chain ring: http://tinyurl.com/66ztbn Look closely at the front tire at 1 & 7 o'clock. Look _very_ closely at the rear tire at 1 & 3 o'clock. Aren't you glad that your choices are limited to tubulars and clinchers? Solid non-pneumatic rubber tires are all they had for high wheelers and that drifted into the safety bicycle, this one apparently by Iver Johnson. I had a later IJ that had triangular taper BB and steel cranks. Realizing that the torsional strength of a shaft is roughly that of the largest inscribed circular shaft, a triangle doesn't leave much and with steel cranks had a poor retaining bolt to boot. Is that not a valve at 7 o'clock on the front wheel? I think that is where a valve wold go for a pneumatic tire, but these may be tire anchor screws to keep the solid tire from walking around the wheel and dismounting itself. I can't see any detail in the large gap in these tires to see their cross section but it seems to be mostly solid rubber. On another note, what was the benefit of the serpentine seatpost? I think it is believed to be a spring similar to the belief that the curl in fork blades are springs. Both tire valves are visible if you look closely. The rear valve, at 3 o'clock, is almost obscured by the chain stays. Here's the original page of photos: http://tinyurl.com/66ztbn You can see the valve caps on both valves. Here they are, cropped from three photos and enlarged: http://i33.tinypic.com/se885v.jpg The holes for the valves are at the riveted rim joint. Someone may have taken the old pneumatic tires and tubes off, leaving the valves in place, and installed "cushion" tires as described in the auction text. Cushion tires were hollow, but not inflatable, so they flexed and wore rapidly. That was my suspicion, considering the non-pneumatic tires. I'd love to see the actual bike and find out exactly what's going on. *** As for the odd seat post, that was just one early shape. It looks strange to us, but it was cheap, easy, and simple to bend a solid rod like that: http://www.auctionflex.com/auctionim..._2BX0U29PG.jpg http://www.auctionflex.com/auctionim..._2BX0U2N4Y.jpg It's very easy to get at the clamping bolt under the seat and then slide the seat back and forth on its long level section to suit the rider. Thanks for the details. I find these bicycle interesting because they often reveal that the ancients were up against difficult design problems and found solutions that are often missing today. Jobst Brandt Dear Jobst, Here's another example of what Carl Sundquist called the serpentine seat post: http://www.auctionflex.com/showlot.a...ction=&lang=En or http://tinyurl.com/67eka4 With no seat in the way, it's easier to see how the post worked. Other companies used wooden-spoke wheels, too. Here's another wooden-spoke bike, with the original wheels included in the auction: http://www.auctionflex.com/showlot.a...ction=&lang=En or http://tinyurl.com/5lflhe This photo shows how early safety bicycle makers were still scratching their heads over frame design: http://www.auctionflex.com/auctionim..._21D1FEP66.jpg You can just barely make out the rear sprocket on the other side of the flip-flop hub mentioned in the auction text. I'm impressed with the notion that a lady circa 1891 was going to stop at the bottom of a hill and flip her rear wheel around for a lower gear. Cheers, Carl Fogel |
#15
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Not your typical tires
On Sun, 02 Nov 2008 19:10:48 +0000, jobst.brandt wrote:
Tim McNamara wrote: I think it is believed to be a spring similar to the belief that the curl in fork blades are springs. There has been some published data measuring vertical flex of bicycle fork blades under load. This flex was measured to be greater in forks with larger offset and a lower, tighter curl at the hub end; also, naturally enough, smaller diameter fork blades showed more flex. The magnitude was small, maybe 1/4" at most. Whether it's *useful* is a different story; the authors of the article believed it was but I can't say that I was convinced. For one thing, the load was static with weights applied to the front of the bike. I think static loads are appropriate for such measurements. As I mentioned in another thread, speed of application of forces is immaterial for structural metals. er, given the fact that deformation at low strain rates does indeed differ from that of high strain rates, that's a ridiculous blanket statement jobst. No doubt forks flex but not enough to constitute a spring, certainly not as much as the pneumatic tire furnishes. ah, that old saw, which contradicted by... Most of the flex in forks takes place in the steertube so what do you want jobst? elasticity or no elasticity? can't pick and choose you know. that generally has a lower bending stiffness than the two fork blades it supports and whose bending load is pivoted about the lower head bearing. This also causes fretting damage to the lower and upper head bearing. jobst, you don't even know what fretting is. otherwise you wouldn't confuse it with brinelling. Time's a little tight this morning, I'll dig up the article and post more specifics. I'm curious what the goal of this study was. i'm curious as to whether you ever had a goal of studying. |
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