Bad math. If 96% efficient = 5.2 mph, then 90% efficient would be 4.875 mph, not 5.1 mph. And that's with worst case efficiency numbers for the chain setup and best case efficiency numbers for the IGH. Based on this, the other calculations are off too. Correct me if I'm wrong.
--- On Thu, 11/19/09, Eric Norris <campyonly...@me.com> wrote: From: Eric Norris <campyonly...@me.com> Subject: [RBW] Internal Hub Efficiency: What the Experts Say To: rbw-owners-bunch@googlegroups.com Date: Thursday, November 19, 2009, 12:35 AM For those who don't have a copy of "The Dancing Chain" laying around the house, here's a summary of what Frank Berto said about internally geared hubs (IGHs), which is itself a summary of extensive bench testing done in 1998: --Standard derailleur systems achieve 98-99 percent efficiency when the chain is running straight, and 96-97 when in cross-chain mode (such as small cog/small chainring) --Internally geared hubs ranged between 80 and 90 percent efficiency, achieving higher efficiency in lower gears. One IGH tested in direct- drive mode was 95 percent efficient. Berto compared a typical rider (generating 1/8 horsepower) riding up a 4 percent grade in a low (31-inch) gear. --With a standard derailleur bike operating at 96 percent efficiency, the typical rider could climb at 5.2 mph at a cadence of 60 rpm --With an IGH operating at 90 percent, the same rider would be 6 percent less efficient, dropping his/her speed to 5.1 mph Those numbers don't sound too bad, at least for shorter riders. A 4- hour ride on a standard geared bike would take about 4 hours and 15 minutes (or less, since the efficiency of the IGH wouldn't matter at all on downhills). However, applied to an event like PBP, an 84-hour time would become 89 hours if the bike became 6 percent less efficient (or, assuming that half of PBP is more or less downhill, 84 hours would become 87 1/2). I'll continue to test this in the field and see how my Quickbeam's 8- speed Sturmey Archer performs. P.S. No, the vaunted 14-speed Rohloff hub was not part of the '98 test. It's hard to see how it could be too much more efficient than other IGHs, but it could be somewhat closer to a standard setup. P.P.S. If you haven't read The Dancing Chain, you really should. It's a fascinating look back at the early days of cycling, and it proves once again that everything "new" in bicycling today was in fact invented 100 years ago. Really. --Eric www.wheelsnorth.org www.campyonly.com -- 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-bu...@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=. -- 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-bu...@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=.
