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I'm trying to convert an old city bike (https://archive.trekbikes.com/us/en/2010/trek/navigator10wsd#/us/en/2010/trek/navigator10wsd/details) for my middle-aged mother who did not do any sports so far. There are a lot of slopes in our town, so I want the gear ratio to be as "easy" as possible.

As you can see in the link, the bike has a 1x 42t front chainring and the cassette goes up to 34t.

How would you do it? The following is what I think:

I believe 34t is ok, but 42t is too much. I looked for other 1x systems but no one sells a 1x chainring with 22t or 24t.

Then I decided to buy a 2x or 3x system with a smallest chainring of 22 or 24t and fixing it to that lowest chainring using a front derailleur and limit screws. (You may ask why am I not installing a full 2x/3x system with gear levers and cables: I really do not think she will need the bigger chainring, and there is no routing for the front derailleur cable. If she starts to ride a lot and needs that second chainring I may think about it.)

Do you see any problem with my solution? To avoid the chain being not linear when the smallest ring is used in the cassette, is it better to buy a 2x system? (Is smallest chainring of the 2x systems are closer to the right side, compared to 3x systems? I guess that would help to keep the chain linear.)

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    You might get more buy-in by retrofitting an electric assistance motor. Climbing is hard - she may choose to ride around hills rather than over.
    – Criggie
    May 24 at 11:19
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    Bear in mind that with a sufficiently low gear, it can be hard to maintain enough forward momentum to keep the bike upright. This will be determined somewhat by the rider's bike-handling skill, but my guess is that anything below a 1:1 ratio (eg 34x34) may be hard to keep upright.
    – Adam Rice
    May 24 at 16:02
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    @Michael It is a 1x, not a single speed.
    – MaplePanda
    May 24 at 20:37
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    @Jakuje Would be cheaper to just buy a new bike I think.
    – MaplePanda
    May 24 at 20:38
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    Lot's of people are suggesting some sort of electrical assist. A front electrical wheel will set OP back over $300. For that price, OP could get a used 2x or 3x bike off craigslist.
    – sam
    May 25 at 2:12
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There is nothing wrong with installing a 3x crankset on the bike, and having her only use the smallest chainring. Some benefits of this solution:

  • This is the cheapest and easiest solution.
  • If the smallest chainring has 22 teeth, her lowest gear ratio will be 22/34, which will make climbing hills very easy.
  • If the smallest chainring is too easy, you can simply move the chain up to the middle chainring, which will probably have 32 or 34 teeth.
  • You will not need to install a front derailleur.
  • Using the smallest chainring and the smallest sprocket (aka having a crooked or non-linear chainline) is not a major problem on modern bikes, as you suggest it might be.
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    I like this no-frill solution. Additoinally, with(out using) the largest ring, there is a lot of room to fiddle with adding a chain guard / chain cover, which would be a sure welcome for the intended use of the bike.
    – EarlGrey
    May 25 at 12:22
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I'm a big fan of low gears (I run a 22 inner ring on my MTB despite being a fairly strong climber), but I'd say a 22 or 24t ring is too small to use as an only ring - it'll spin out much to easily on slight downhills or with tailwinds.

You can get 1x cranks for MTB that come as standard with a 30T ring, and aftermarket 28T rings - I'd suggest these would be a better compromise.

As another alternative, if you are doing a conversion anyway, perhaps you might like to consider an aftermarket e-bike conversion?

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I would suggest you go with an IGH (internal geared hub), a 29T front chainring and a 24T on the back.

It works, the only caution needed is that shifting while pedaling hard should be avoided, otherwise the internal of the IGH will wear out quickly ... I don't think this will be an issue for your low-power mother.

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    That upgrade would cost much more than the bike is worth.
    – mattnz
    May 24 at 20:53
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    @mattnz how much is the proper bike fitting worth to the OP's relative? sometimes it has an infinite value: a comfortable bike will be ridden, an uncomfortable one will sit in the garage unused :)
    – EarlGrey
    May 25 at 7:39

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