I agree with Ted on the problem of getting Ideal Cog Teeth & first cogs being too small (11T & less) , but I believe a 46-36-26 triple with a wide range Shimano HG-400 12-36 9 speed cassette (Deore RD-M591-SGS), 130mm OLD Tiagra 4000 rear hub, and 650Bx38's gives me: good gearing in my cruising range (75 to 55gi) with 3 cogs to use in the Outer and Middle rings an even 16% to 12% gearing change between all the cogs. good chain line (<= 0.040% chain stretch) over a 6 cog range on each chain ring (front CL's of 52, 44, 38mm & rear CL of 44mm) good high/low range (101 to 19 gi) good FD performance with old school style FDs (using a 9 speed Sora FD-R3000, but also used a 1980's Shimano FD-MT60)
The learning for me was to be willing to shift between the Outer and Middle rings *much more often *than I thought before, e.g. shift to Middle 3 cog when using the Outer 4 cog and the terrain indicates a need for lower gearing. Before I tended to stay on the Outer ring too long. Now, the outer and middle rings are used much more evenly. The 10T ring difference makes shifting the rings easy. The 26T Inner is still for big hills, but I feel I get to it more efficiently than before. The triple limits you to a 44T Outer (FD cage hitting the C/S with a 42T). but the 46T/12T combo gives me the 100 gi high I want with 650Bx38, so I see the chain ring size limit as theoretical limit I don't encounter as long I have a large stock of HG400-9 12-36 cassettes. *As for Leah's problem *with shifting to lower gears, I think Sheldon said it best (paraphasing), "when you come to hills, shift to your lower gears before you need too". Easier said than done. John Hawrylak Woodstown NJ On Saturday, May 20, 2023 at 1:55:27 PM UTC-4 Ted Durant wrote: > Hi All - > > Leah's "Getting Over My Head" thread seems to have evolved into a gearing > thread. I retired from a career in data mining and statistical modeling, so > you can just imagine how much time I've wasted on "optimizing" bicycle > gearing. > > Here's the TL;DR version: it's impossible to optimize gearing, so stop > sweating it. > > The slightly longer version is that we are locked into integer tooth > counts; when the optimal cog is 14.5 teeth, that ain't an option! So, we > are forced into compromising or, better yet, satisficing. > > There are essentially three key points we are trying to fix with gears: > the lowest low, the highest high, and the steps in between. Given those, we > then try create a system that reliably and easily shifts among the gears. > For me, a 2x system using components available today provides the best > combination of low-low, high-high, steps in between, simplicity, > consistency, and reliability. But that depends highly on the chain, the > chainrings, and the front derailer playing nicely together. It also works > for me because I use it as 2 gearing ranges, one for flats and downhills, > the other for long, steeper uphills. > > The lowest low and the highest high are pretty straightforward, and plenty > of ink has been spilled on how to choose those, so there's no point in > elaborating on that. It's the "steps in between" part that drives us wild. > In theory, we think, we'd like to have perfectly even steps between the > high and low. In practice, though, 1) that's simply not possible with a > cog-and-chain drivetrain, and 2) it might not even be that desirable. A lot > of riders, myself included, find that we prefer smaller steps between gears > in the range in which we normally ride, and larger steps out in the > extremes. > > What I definitely don't like is having a big difference between 3 adjacent > cogs in the middle of my cruising range. For example, a 1-tooth difference > one way and a 2-tooth difference the other. Unfortunately, this is a common > occurrence in large cog count cassettes with tiny small cogs - they go from > a 1-tooth difference to a 2-tooth difference near the middle of the > cluster. That's twice the amount of reduction/increase in effort. So, when > I'm looking at cassettes, I'm looking for ones where that 1-to-2 transition > occurs as close to the small cog as I can get it. A major factor here is > the movement to smaller smallest cogs, which has gone from 14 to 10 in my > time. Starting from 11 (or, God forbid, 10!) you use a lot of cogs to get > to the point where 2-tooth steps start to make sense. > > On the other hand, those small smallest cogs mean we can use small outer > chainrings, and that's something of a boon if your front derailer can > handle it, because it means we can also use smaller inner rings on a 2x to > get sufficiently low gearing. The difference between chainrings is worth > examining a bit. Typical road double front derailers have a 16-tooth max > difference specification, which derives from the standard "compact double" > 50-34. That's a 39% difference, which is a pretty big jump, roughly 3.3x > the average jump on the cassettes often paired with those chainrings. So, > shifting up front is the equivalent of around 3 1/3 cogs in back. On my > Waterford I use a 42-tooth large ring, and a 26-tooth small ring is 16t > smaller, but that's a whopping 48% difference, which is 5x the average jump > on my cassette. Piaw mentioned going with smaller tooth differences up > front, and there's a good example of why. When I built my Breadwinner I > went with 44x32 up front, a 32% difference that is 3.1x the average > difference on the cassette. I find that to be a much less disruptive change > than on my Waterford. The front chainring difference as a multiple of the > average in back turned out to be a significant factor for me. Sure, it > means I have more overlap in gears, but that's less important to me than > the change in cadence caused by shifting. > > One last consideration as I'm designing a drivetrain is that I want my > preferred cruising gear near the center of the rear cogs, maybe a little > closer to the small end, so that I can be on the large ring for most of my > riding around home. That's around a 5.0 gain ratio for me now, which is the > 42x17 on my Waterford. And, as noted, I want a consistent difference above > and below that gear, which means, for me, a 2-tooth change on each side of > it. > > 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/95d203f7-162c-4372-b3a1-67dc620f4751n%40googlegroups.com.
