fuzz2050

Imagine a wide range double with 45-26 chain-rings (just the middle and inner of a triple), now pair that to a corncob-style cassette, 16-32 in steps of 2 (16,18...)

Gear inches comes out as this
76.4 44.2
67.9 39.2
61.1 35.3
55.6 32.1
50.9 29.4
47.0 27.2
43.7 25.2
40.8 23.5
38.2 22.1
minimal overlap, close spacing, and it goes as low as I need. Not much of a high end, but I can live with that. Perhaps best of all, no crazy shifting pattern, straight down the big chainring, then onto the small.

Is chainline going to be the death of this idea? or something more insidious yet? There must be a reason why I haven't seen it somewhere else.

Jeff Wills

It's somewhat similar to Sheldon's Hetchins: https://sheldonbrown.org/hetchins/index.html

If I were doing something similar, I'd do it more like Sheldon's- set up the cassette so I spent most the time on the big chainring and use the little chainring for a bail-out. With your setup, you'd upshift on the cassette to the small/small and then immediately shift to the big/big. That's a lot of action on behalf of the derailleurs to make one "step".

prathmann

Looks like reasonable gearing for a work/cargo bike, but I wouldn't want to be that limited on the high end for a regular road or touring bike. Not only is the maximum gear too low, but the jumps at that end are fairly large.

DannoXYZ 

First, calculate the differences between the cogs in terms of percentages, not teeth. The jump from 16-18t is HUGE compared to the jump between 30->32t.

Shifting from 26t to 45t chainring will be difficult. You may find yourself doing that shift a lot at lower speeds. The 26t will only be used on the steepest of hills, so you'd only really use the 18t, 24t and 32t.

The main objection I have to using this would be the large jumps between gears. You end up spinning too fast in one gear and too slow in the next.

AEO

you want smaller jumps in the higher range.
the big 3 understand this and that's why the higher end is spaced in 1T jumps while the lower end has larger jumps of 2~4T

pacificaslim

Can one even get a chain to go directly from a 26 to a 45 chainring? That's a huge jump.

tatfiend 

It was routinely done for years on half step + granny drivetrains pre indexing. Per Frank Berto actually easier than a 24, 36, 48 triple as the shift from 24 to 36 is difficult due to how far below the derailleur the 36 tooth chainring is. IIRC his touring triple was a 24, 45, 50 setup in front.

Retro Grouch 

I did something like that once. It was a PITA to ride.

Since there's no overlap, you don't have very much choice when to make the double shift. If you make the shift into the small ring before you start up the hill, you may spin out and lose momentum. If you wait until you're actually climbing the hill, you will definitely lose every bit of your momentum.

Sometimes overlap is good.

fuzz2050

Yep, that's why I had the idea. My current set-up is a 50-45t-26. I have no problem with that shift.

The awkward double shift did occur to me, but with friction bar end shifters it should be doable. Awkward, but doable.

The fact that RetroGrouch pointed out, that because of the minimal overlap, you don't really have a choice as to when that shift is, well that didn't.

and anyone know an online gear inch calculator that can go by percent change?

DaveSSS 

I've seen this proposed many times. The flaw in the logic is that minimal overlap is a good thing. It's not.

The real extreme was something like a 53/27. It could be used with a common 12-25 cassette to provide close cog spacing, but when you get the to 53/23, you'd need to shift 7 cogs smaller, to the 27/13 in order to produce a uniform progression toward lower gears. That would be awful, but it could be made even worse with a smaller little ring.

With regard to percentages, the common 12-25 or 12-27 cassettes have sensible percentage changes. They are all 1-tooth shifts until you get to the 17, then it changes to 2T jumps. It's unavoidable that the percentage between a 12-13 is larger than the 16-17. At 17-18, the percentage becomes so small that it's not often valuable, except for flatlanders.

MTB cassettes are made with much larger jumps, usually with all 2T or larger jumps or 16% rather than the 8% found on road cassettes.

tatfiend 

The most thorough writeup on gear train types and characteristics I am aware of is in Frank Bertos 1988 book done for Bicycling Magazine on upgrading road bicycles. What you are proposing is called a "Wide Step" there and Frank noted it is a PITA for the reason already noted by several posters. A case of it looks good on paper but riding it is another matter.

Currently 24 copies of the book are listed as available on Amazon, the cheapest starting at 12 cents plus shipping. Recommended for gear train experimenters.

https://www.amazon.com/Bicycling-Maga...3643704&sr=8-3

DannoXYZ 

Personally, I want a 13-26t straight-block with 34/52t crankset.

Jeff Wills

Dooode! A 13-26 straight block would have 14 cogs!

Although I have an old Mighty Tour crankset sitting in the garage... it would be easy enough to dig out a 34 and a 52 from the pile o' parts.

oldpedalpusher

Your idea of disparate chainrings with close rear cogs is a good way to minimize double shifting. I did something similar because I wanted low gears, but without running a large heavy rear cassette... and I didn't want the need to double shift to get a gear. Instead of a very wide double, I put a 24-34-44 mountain triple on my road bike with an ultraclose ratio "corncob" 12-13-14-15-16-17-19-21 rear cassette





I noted which ratios I liked to use for each specific riding situation, and then grouped them accordingly to each front chainring. The result is nice very evenly spaced ratios without any weird chain angles from 31 to 99 gear inches.

Small: 31-34-38-41 for climbing

Middle: 44-48-54-57-61-66 for upgrades, and headwinds

Large:70-75-79-85-91-99 for level, downgrades, and tailwinds

Chris_W

I'm running similar setups on my bikes right now. On the touring and cyclocross bikes I have 26/42 chainrings. The jump between these is fine, and is not a problem when prepared for properly. On the road/racing bike, I have 28/46 chainrings. This jump is a bit large, and you really have to be prepared in order to not loose momentum. The cassette is always a 10-speed 11-26 or 12-26.

The front shifting is not smooth, but the setup is designed to have minimal front shifting - I can stay in my big ring 95% of the time, and just use the small ring as a bail-out. With 10 cogs on the back, there is really no need to overlap gear combinations on different rings. These setups really are just like the old "half-step-plus-granny" triple setups - those were used when there were only 5 to 7 cogs on the cassette, now that we have 9, 10, or 11 then the two large chainrings can be replaced with one to achieve the same gear combo's.

Your cassette choice sounds really weird to me, the cogs seem unnecessarily large and you need to get the percentage spacing even instead of the tooth count spacing. Even if you can't find an online gear calculator to give you the percentage changes, just put the numbers into a spreadsheet program and have that do the calculations for you while you play around with different options (if you don't already have Excel, then get OpenOffice for free).

These kinds of setups have been discussed quite a bit in the Long-Distance Cylcing sub-forum, head over there and search for words like "super compact."

AEO

https://www.panix.com/~jbarrm/cycal/cycal.30f.html

more detailed gear calc compared to sheldon's

fuzz2050

The cassette choice was somewhat arbitrary, and easily tune-able to get actual consistent percent changes, however, it seems the idea itself has enough flaws to not be worth pursuing with a passion. Well, maybe worth doing just for fun, but at least I have a better idea of what to expect.

HillRider

Campy offers something pretty close with their 13x26 10-speed cassette. It's a straight block from 13 to 19 then two tooth jumps for two cogs (21, 23) and one three tooth jump (to 26). The crank is also quite feasible. Get a compact crank and swap out the big ring.

Jeff: Shimano has patents fron the early 1990's for a 14-cog cassette and a specific matched chain design so the concept, if not the commercial application, is out there.

Retro Grouch 

Am I remembering right in thinking the patent includes a 1-sided chain?

davidad

No. The chain is an oddity from the early safety bikes. The inner plates are arced over the cog teeth.

davidad

My tourer is set up as a half-step with a grandpa gear. The range is from a 16 to 107". It is a seven speed with an 11-34 cassette and a 20-40-44 front.The shift from the 20 is not a problem. I use downtube shiffters on both of my Herons.

DannoXYZ 

Yeah, I've been running compact-crank since 1993 even before that nomenclature was around. I used a TopLine MTB crank on my road bike to get the 34t inner ring. When 7-spd was standard, I made my own 9-spd cluster by sanding down the spacers between the cogs and welding a 12t cog onto the threaded 13t cog on a Uniglide cluster. I might just try the same with a 10-spd cluster to make at least a 12-spd cluster. Chain-width is an issue and I may only be able to get 11-spd though.

fuzz2050

damn, how do you get a 20 tooth great great grandfather gear? That's smaller than even MTB standards will allow.

DannoXYZ 

He's probably using one of those adapters that lets you use freewheel cogs on your crank.

Jeff Wills

Well... "current" MTB standards only allow a 22 tooth. Back when Suntour introduced "Microdrive" cranksets, the inner bolt circle was 56mm. This allows a 20 tooth small ring. Later, Shimano introduced 5-arm MTB cranks where the inner BCD was 58mm, limiting them to 22 teeth. Here's some archival info on the Suntour cranks: https://www.bikepro.com/arch_products...our-crank.html

Or maybe he's got a Mountain Tamer (https://abundantadventures.com/quads.html) adapter- this allows a "chainring" down to 16 teeth if you can find the required Suntour freewheel cog.