Actual, the polar moment of inertia is to the 4th power: PI()(D^4-d^4)/32. Cheers! James Valiensi, PE Northridge, CA H818.775.1847 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 <[email protected]> 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." <[email protected]> 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 <[email protected]> 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 [email protected]. > > To unsubscribe from this group, send email to > > [email protected]. > > 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 [email protected]. > To unsubscribe from this group, send email to > [email protected]. > 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 [email protected]. > To unsubscribe from this group, send email to > [email protected]. > 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 [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/rbw-owners-bunch?hl=en.
