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To me, the left side on a bike that doesn't have a rear disc brake is being somewhat wasted.

So how about this idea... on the right side have the normal gears but on the left side, have a freewheeling granny gear. So you would have 2 chains but also some type of clutch so you could switch between the granny gear and the normal gears. The granny gear could be something incredibly low such as 20/50 but the smallest cog on the main gearset could be much more reasonable such as 34 or even 28. This would help alleviate the big jump of 10 or more teeth on the granny cog found in MegaRange type gearsets. By isolating the granny gear, the cassette tooth jumps (between gears) can be made more reasonable. Perhaps they could even integrate a disc brake and the granny sprocket in one, with the caliper being positioned in the opening where there is no chain. Perhaps run a concentric ring close to the teeth to hold out any grease from hitting the brake pads. That would be something to behold.

Actually, the granny gear can be enabled all the time since the road speed would almost always exceed that of the granny gear so the pawls on it would not engage. The lowest normal gear would always be faster than the granny gear, just like if in a gear you pedal at half the speed required to maintain road speed, the gear will not engage the pawls. When the rider wanted to actually use the granny gear, he/she would have to disable the main gears (via some type of clutch), then pedal fast enough to engage the granny pawls. So maybe when anticipating a large hill, one could clutch out of the main gears, coast down to walking speed, pedal fast (about 100 RPMs), and then the granny gear would engage. 20/50 (0.4) would be a hell of a hill climbing gear. With 26" tires, that would be 10.4 gear inches. Wow!

Also if you were really slick, you could make the granny gear so that the chain is the same length as the main chain so if perhaps your main chain breaks, you have a backup with you. There are some combinations of sprockets that would make the chain lengths the same (or at least very close). Also if you rarely use the granny gear, you could half wear out the main chain and then swap them so you get better performance on the main chain and longer gear life.

I know if I had a 20/50 (0.4) low gear I would use it a lot. That would be awesome.

So the question is can this be made to work and if so, has anyone tried it yet?

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    Combination granny sprocket and disc brake is brilliant. You may want to keep that to yourself and get a patent. That 3+3+3 idea with dual ramping - no one else is doing it - you may want to check into a patent on that also.
    – paparazzo
    Jan 21, 2016 at 16:43
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    And your question is? (I don't see a single question mark in the text, and the title doesn't qualify as a full question to me...)
    – anderas
    Jan 21, 2016 at 16:45
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    You are too generous. Maybe hold back on some of your best ideas. There is a patents.stackexchange.com if you want to further explore patents. You can lock up a provisional patent for like $300 and then pitch your idea(s) to the big boys like SRAM and Shimano.
    – paparazzo
    Jan 21, 2016 at 17:00
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    I think that this is a lot of complication for something that wouldn't be much benefit over a triple chainring. Using chainrings with 48-36-26 with a 12-30 cassette would give a plenty easy "granny gear" for the hills most people would willing to approach on a bike. Having a 20-50 super-granny gear as you propose would mean you were only going 4.5 km/h at 90 RPM, which is less than walking speed. At that pace, you might as well get off the bike and walk, as it will be more energy efficient.
    – Kibbee
    Jan 21, 2016 at 19:42
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    David - you seem to have a mad addiction for low low low gearing. Perhaps your engine needs work, rather than your transmission.
    – Criggie
    Jan 21, 2016 at 21:32

1 Answer 1

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I say it is both possible and practical. If someone really wants the crawler gear then this is a way to get it without having to resort to other methods such as a double gear reduction (chainring and cogs being only 1 reduction then adding some other one). If someone ever tries this then please report back. I would love to have a bike with this isolated very low gear so then I could just use reasonable size cogs and chainrings.

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