Re: [RBW] Stem Strength
OHH! I knew that, once upon a time! Cheers, back! On Saturday, May 7, 2011, James Valiensi valie...@mac.com wrote: Actual, the polar moment of inertia is to the 4th power: PI()(D^4-d^4)/32.Cheers! James Valiensi, PENorthridge, CAH818.775.1847 M.818.585.1796 On May 7, 2011, at 5:29 AM, Ken Freeman wrote: Ok, so the steel stem has a larger OD AND a stiffer modulus. Staying on the back of an envelope, the ratio of 31.6^2 to 22.2^2 is about 2. In which case your calc requires the ratio of moduli to be about 5. For steel it's about 30,000 ksi and for aluminum it's about 10,000 ksi. Not bad, for the back of an envelope, and no finite element work!! On Sat, May 7, 2011 at 1:15 AM, James Valiensi valie...@mac.com wrote: Hey, My back of the envelope calc's indicate a standard aluminum quill stem will deflect about ten times more than a steel stem. This is with equal extensions lengths and loads, and the aluminum stem has a solid 22.2mm diameter extension, and the steel stem is 31.8mm OD w/ 25.4mm ID extension. The extension into the fork vs. clamping on the outside of the fork are not significant here. By the way, neither stem deflects that much. If you really want a stiff stem, use a short extension, and big diameter. And steel too. And you know why they went to 31.8mm diameter handle bars? Because of the stinking cable grooves. The grooves make the bar section too flexible, the bigger diameter overcame this. Cheers! James Valiensi, PE Northridge, CA H818.775.1847 M.818.585.1796 On May 6, 2011, at 6:44 PM, Philip Williamson wrote: When I got my Quickbeam, I tried a couple of stems, including the stock Technomic Deluxe and the Nitto Dirt Drop. Both flexed noticeably more than the Salsa welded stem I ended up with. The Dirt Drop not as much as the Technomic Deluxe, but the quill was bottomed out in the steerer. Philip On May 6, 9:24 am, Bill M. bmenn...@comcast.net wrote: Back in 1991 I bought a Cannondale (very stiff frame) that came with a standard quill stem. I swapped it out for a hollow, welded stem that had a much larger diameter extension. The first time I stood up and cranked the bike up a short steep rise I was astonished at how much stiffer the front end of the bike felt. The quill stem was allowing the bars to twist, the new one wasn't. That may or may not be seen as a good thing, but I have no doubt that typical threadless stems are stiffer in torsion than traditional quill stems. Bill On May 6, 3:58 am, MichaelH mhech...@gmail.com wrote: The new RR contains an article by GP outlining his believes about various aspects of bike strength, comfort, weight, and comfort. There wasn't much new there for anyone who has followed him for a few years, including why he prefers threaded headsets and stems, but it did trigger this question from me. My son, who is 39 years old and a very muscular 170 lbs claims that he experiences stem flex while climbing with a traditional quill stem. I am always disinclined to challenge people's subjective experience but I have never experienced this and suspect it is in his imagination. Has anyone here felt their stem flex and has anyone ever broken a stem? michael -- You received this message because you are subscribed to the Google Groups RBW Owners Bunch group. To post to this group, send email to rbw-owners-bunch@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en. -- You received this message because you are subscribed to the Google Groups RBW Owners Bunch group. To post to this group, send email to -- You received this message because you are subscribed to the Google Groups RBW Owners Bunch group. To post to this group, send email to rbw-owners-bunch@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en. -- You received this message because you are subscribed to the Google Groups RBW Owners Bunch group. To post to this group, send email to rbw-owners-bunch@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en. -- Ken Freeman Ann Arbor, MI USA -- You received this message because you are subscribed to the Google Groups RBW Owners Bunch group. To post to this group, send email to rbw-owners-bunch@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en.
[RBW] Stem Strength
The new RR contains an article by GP outlining his believes about various aspects of bike strength, comfort, weight, and comfort. There wasn't much new there for anyone who has followed him for a few years, including why he prefers threaded headsets and stems, but it did trigger this question from me. My son, who is 39 years old and a very muscular 170 lbs claims that he experiences stem flex while climbing with a traditional quill stem. I am always disinclined to challenge people's subjective experience but I have never experienced this and suspect it is in his imagination. Has anyone here felt their stem flex and has anyone ever broken a stem? michael -- You received this message because you are subscribed to the Google Groups RBW Owners Bunch group. To post to this group, send email to rbw-owners-bunch@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en.
Re: [RBW] Stem Strength
Is his stem extended beyond the minimum insertion mark? It may not be tight against the steerer tube ID. From: MichaelH mhech...@gmail.com To: RBW Owners Bunch rbw-owners-bunch@googlegroups.com Sent: Friday, May 6, 2011 5:58 AM Subject: Re: [RBW] Stem Strength My son, who is 39 years old and a very muscular 170 lbs claims that he experiences stem flex while climbing with a traditional quill stem. I am always disinclined to challenge people's subjective experience but I have never experienced this and suspect it is in his imagination. Has anyone here felt their stem flex and has anyone ever broken a stem? -- You received this message because you are subscribed to the Google Groups RBW Owners Bunch group. To post to this group, send email to rbw-owners-bunch@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en.
Re: [RBW] Stem Strength
I'm nowhere near as cut as your son, and I felt the difference when I tried a stem extender with a modern-style stem instead of a standard Nitto or such. The rocking of the handle bar when I cranked it was less. I didn't feel the difference was very significant. Plan is to go back to a Nitto based on looks. Stem flex is a far cry from stem breakage. Well-made parts are able to take literally millions (at least) of cycles of elastic flexing (NOT inelastic) before fatigue begins. Metal fatigue is what leads to fracture. Additional factors include the presence of stress risers due to deep scratches, overly sharp edges, or casting flaws that might cause internal stress risers. On Fri, May 6, 2011 at 6:58 AM, MichaelH mhech...@gmail.com wrote: The new RR contains an article by GP outlining his believes about various aspects of bike strength, comfort, weight, and comfort. There wasn't much new there for anyone who has followed him for a few years, including why he prefers threaded headsets and stems, but it did trigger this question from me. My son, who is 39 years old and a very muscular 170 lbs claims that he experiences stem flex while climbing with a traditional quill stem. I am always disinclined to challenge people's subjective experience but I have never experienced this and suspect it is in his imagination. Has anyone here felt their stem flex and has anyone ever broken a stem? michael -- You received this message because you are subscribed to the Google Groups RBW Owners Bunch group. To post to this group, send email to rbw-owners-bunch@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en. -- Ken Freeman Ann Arbor, MI USA -- You received this message because you are subscribed to the Google Groups RBW Owners Bunch group. To post to this group, send email to rbw-owners-bunch@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en.
Re: [RBW] Stem Strength
on 5/6/11 3:58 AM, MichaelH at mhech...@gmail.com wrote: My son, who is 39 years old and a very muscular 170 lbs claims that he experiences stem flex while climbing with a traditional quill stem. I am always disinclined to challenge people's subjective experience but I have never experienced this and suspect it is in his imagination. Has anyone here felt their stem flex and has anyone ever broken a stem? I've definitely felt (and feel) front end flex, but am never quite sure how to parcel it out to the various bits, and the varied conditions under which I apply pressure to the pedals. My unsubstatiated belief is that once you start focusing on it as something unwanted, you find flex in a lot of places. Bars flex a bunch, of course, and I've always felt that was where most of the movement came from. If I'm really honking on the bars, I'm probably out of the saddle, and there are extensive variables in perception and power when that occurs. Wheels flex, bb's flex, frame flex... if there is actually stem flex, I always suspected it's fairly far down the chain. (Now, I've also felt a notchy movement of a quill stem when it was in a bulged steerer, but that's really a different animal.) Of course, much of the discussion regarding flex is based on the assumption that it is a bad thing, and that's something I no longer take on faith. At one point in the last century, Ibis Ti Stems were the peak of bling. They were beautifully made quill stems, and I know a few people who had them. Flex was not on their list of descriptors. I have Ti bars on my soft-nosed multi-geared mtb (which largely sits dormant...), and they are connected by fairly stiff threadless stem. Again variables of front suspension cloud the equation. But, when I stomp and pull to accellerate, there's a fair amount of give. - Jim -- Jim Edgar cyclofi...@earthlink.net Cyclofiend Bicycle Photo Galleries - http://www.cyclofiend.com Current Classics - Cross Bikes Singlespeed - Working Bikes Your Photos are needed! - Send them here - http://www.cyclofiend.com/guidelines I threw one leg over my battle-scarred all-terrain stump-jumper and rode several miles to work. I'd sprayed it with some cheap gold paint so it wouldn't look nice. Locked my bike to a radiator, because you never knew, and went in. -- Neal Stephenson, Zodiac -- You received this message because you are subscribed to the Google Groups RBW Owners Bunch group. To post to this group, send email to rbw-owners-bunch@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en.
Re: [RBW] Stem Strength
Electrical and systems, but some ME knowledge is fundamental to engineering for vehicles and other stuff I've worked on. On Friday, May 6, 2011, Brett Lindenbach brett.lindenb...@gmail.com wrote: ken, you sound like a mechanical engineer. thanks for your insight... -- You received this message because you are subscribed to the Google Groups RBW Owners Bunch group. To post to this group, send email to rbw-owners-bunch@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en. -- Ken Freeman Ann Arbor, MI USA -- You received this message because you are subscribed to the Google Groups RBW Owners Bunch group. To post to this group, send email to rbw-owners-bunch@googlegroups.com. To unsubscribe from this group, send email to rbw-owners-bunch+unsubscr...@googlegroups.com. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en.
