Re: [RBW] Re: Gearing Choices
On Wednesday, April 3, 2024 at 12:16:23 PM UTC-5 Patrick Moore wrote: Piaw: It's easy and, thanks to AliExpress, relatively cheap to build your own cassettes from loose parts Thanks to some coaching from Patrick and Garth, I sourced from Ali Express the necessary cogs and spacers to build a 7-speed 11-13-16-19-23-28-34 cassette. It looks pretty snazzy with the red spacers and silver cogs. It's not going to win any awards for light weight, but I mounted it to a standard 8-11 speed freehub (using an extra spacer and cog to fill the gap), and it shifts beautifully with a Cyclone GT rear derailer and Silver downtube shifters. I didn't get any ghost shifting, but I also 1) tightened the shifter a bit and 2) didn't stand on the pedals. I had 39 and 42 chainrings in inventory, so I mounted those, as well. Ideally I'd have a 4-tooth difference up front, but this is good enough to test the hypothesis. I only did a quick neighborhood loop - flat, but with a fair amount of wind. My initial impression is that the steps are too small. Seems crazy, I know, but 10% steps feel small, and the ~20% steps in back feel only slightly too big. It feels amazing, though, to shift two cogs in back and get a huge change in effort. I played around with some alternatives, and I think 12.5% up front and 25% in back would be better for general riding (typical Wisconsin hills and wind, not trying to set Strava PRs). Any more than 6 cogs in back, though, and you'll be going to either a derailer dropper or a newfangled, ugly derailer with a big max cog clearance. If you're willing to go that route you can build a gearing setup with a massive range and perfectly even steps out of a 2x7. Ted Durant Milwaukee WI USA -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/rbw-owners-bunch/d33b80d5-aeb3-4443-944c-8847bf2ee4b7n%40googlegroups.com.
[RBW] Re: Gearing Choices
Ted So, you have settled on what your gearing and derailleur choices will be? If yes, what exactly will they be? What rear wheel OLD will you be using? Will it be a cassette rear hub or a freewheel? How many cogs in back, what cogs? If it's a contemporary 10 or 11speed cassette width, have you confirmed your Suntour RD will sweep that horizontal distance? What shifters will you use? Bill Lindsay El Cerrito, CA On Wednesday, April 3, 2024 at 8:53:56 AM UTC-7 Ted Durant wrote: > This might be a fairly long post, apologies in advance, and just skip past > it or delete if you’re not interested in another treatise on gearing. > > I’m in line for a fancy custom bike and I’ve spent an inordinate amount of > time (it’s good to be retired) working on the gearing. Part of the quest is > that I want a normal-looking silver rear derailer. Given the direction the > industry is headed, and the uncertainty over the fate of the OM-1, this has > been keeping me up at night. > > So, gearing…. I’ll start with the three basic quantitative decisions: 1) > high and low gear, 2) how many cogs and chainrings, and 3) the spacing > between each gear. In some sense you could say that (3) is dictated by (1) > and (2), but a significant question is whether you want equal spacing > across all gears or closer spacing in some and wider in others. > > Starting with (1), we are immediately faced with how to measure a gear. > Most people who spend any time with this still use “gear inches” which, > while a quaint throwback to high-wheelers, is a reasonably intuitive metric > and lots of people immediately know what you mean when you say you’re > riding a 67” gear. For reference, in the 1980’s the standard 12-speed was > set up with a 53/39 crankset and something like a 13-24 set of cogs in > back. That’s a high gear (on 700x25c tires) of 108” and a low of 43”. > > St. Sheldon annointed the Gain Ratio as the preferred metric, and for a > long time that’s what I tried to follow. It adds in the effect of crank > length, and you can think of it as the distance the bike travels relative > to how far your feet travel. That 80’s 12 speed, with a 170mm crank, has a > high Gain Ratio of 8.1 and a low of 3.2. It’s clever and theoretically > superior, and I know that a Gain Ratio a bit under 5.0 is my normal gear, > but it just hasn’t taken root for me. > > A simpler ratio would be the gear ratio itself, which doesn’t take into > account wheel size or crank length. It’s pretty easy to calculate that a > 52x13 is 4x, and 39x13 is 3x, and 39x24 is, well, a bit more than 1.5x. > Different wheel sizes may or may not matter to you. > > In my noodling on this I had a blinding flash of the obvious. What really > matters is how fast (or slow) I am going. For that, of course, I need to > know the cadence I am riding at. Everyone has (this is scientifically > proven, seriously) a preferred cadence, and a comfortable range around that > cadence. There is a pretty wide range among people of their preferred > cadence and range. So, I decided on my comfortable cadence and range, and > now I measure gears (taking into account wheel size) in the speed I am > going at my comfortable cadence. > > The notion of comfortable cadence range then can play a major role in > determining how much spacing you want between gears. For example, my > comfortable cadence is around 87 rpm (aside - I’ve gone to shorter cranks), > and the range is 75 - 100. An ideal shift for me is one that takes me from > the limits of that range back to the center, which is a 14% difference. > (footnote: I measure differences as the natural log of the ratio, happy to > explain why but I don’t think it’s important here.) > > Alas, we are limited to 1-tooth differences, and sometimes 2-tooth > differences. And while a 10-11 change is 9.5%, a 14-15 change is 6.9%. The > evolution to smaller smallest cogs in back has significantly increased the > challenge to building a set of cogs with consistent differences across the > range. If you want a 14% change, you’re kind of stuck down at the small end > of the cogs, choosing between 10% or 20%. Even starting with a 12 tooth cog > helps considerably, as the 12-14 jump is 15.4%, which is very close to > ideal. On the other hand, starting with a larger small cog means having to > go to even larger large cogs to get a desired low gear, or widening the gap > in front, or going to a triple. > > Alright, so there are essentially two approaches to using multiple > chainrings to arrive at a desired range of gears with even steps: crossover > and half-step. In a crossover system, you try for even, acceptable steps > between cogs in back, and when you run out of gears in back you cross over > to the other chainring. In a half-step system, you try for even steps that > are twice the desired difference and the chainring difference half of that. > So, you are making rough adjustments in back and fine
Re: [RBW] Re: Gearing Choices
Piaw: It's easy and, thanks to AliExpress, relatively cheap to build your own cassettes from loose parts -- at least, perhaps not for really huge cogs. But a half step + granny could give me, anyway, nice close cruising gears in the 75" to 60" range plus a downhill gear or two and some low bailout gears. I did this long ago for a commuter with 48/45 or 47/44 rings and a 7 speed cassette, something like 13-32, half-stepping (more or less) the middle 5 cogs with cruising gears in the middle, and using the small for a downhill gear and the big for a bailout gear: 25" wheel: 48 45 12 100 13 92 87 15 80 75 17 71 66 20 60 56 24 50 47 32 35 BTW, this shifted very nicely from hoods, ramps, and hooks with Kelley Take-Offs, on pavement; would not want KTOs on bumpy dirt. Generally speaking, though, with 9 cogs or more I prefer crossover, and I'll trade top high and bottom low for close middle ratios; with a 10 speed cassette giving many more possibilities and the new knobby 50 mm Oracle Ridges requiring slightly lower sandy dirt gearing, my Matthews "road bike for (sandy) dirt" has a sub-compact plus granny: 28 1/2" wheel: 44 28 14 90 15 84 16 78 17 74 18 70 19 66 20 63 40 22 57 36 25 50 32 28 45 29 On Wed, Apr 3, 2024 at 10:54 AM Piaw Na wrote: > I'm a big fan of half-step + granny for 7-speed rear cassettes and > freewheels. I think I even wrote an article about it for the Rivendell > Reader at one point (good luck digging it up!). What killed it for me was > once cassettes got to the point where constructing your cassette was no > longer supported or too much work, it was no longer practical -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/rbw-owners-bunch/CALuTfgutvKBCwCpnU6LzuW0kJDznCdnqkPwfiwV0oaQVraevjQ%40mail.gmail.com.
[RBW] Re: Gearing Choices
I'm a big fan of half-step + granny for 7-speed rear cassettes and freewheels. I think I even wrote an article about it for the Rivendell Reader at one point (good luck digging it up!). What killed it for me was once cassettes got to the point where constructing your cassette was no longer supported or too much work, it was no longer practical. Around here in the Bay Area, I simply decided to go for the lowest gear possible, and live with suboptimal flat riding gearing. The reason for this is even if I can climb a 20% grade when fresh on a 34x34 drivetrain, there will come a day when I have to climb that grade tired, or when carrying a load, or when I just not feeling like working that hard. Going 1mph slower on the flat by contrast just doesn't bother me that much. Just the other day I took my wife on a ride up the Wallace Stegner trail. We'd hiked that trail a couple of times but to my surprise my computer read a 20% grade. Her ebike had to work to get over it and I got into my 40x51. Having that on my bike makes me more likely to ride trails like that. Those who live in places where 20+% grades are unusual or cannot be found probably won't bother with my low gears. -- You received this message because you are subscribed to the Google Groups "RBW Owners Bunch" group. To unsubscribe from this group and stop receiving emails from it, send an email to rbw-owners-bunch+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/rbw-owners-bunch/1879f7ee-a5be-4c00-a74e-53b31624191fn%40googlegroups.com.
