Kids's 20" Fat Bike

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Kids's 20" Fat Bike
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flag maestroman21
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Posted: Oct 11, 2022 at 11:28 Quote
Hello forum, I have a 20" Specialized Fatboy 20" for my kid. Before this year, the bike was used with a towee primarily and just needed to go downhill. This year however, my kid can likely climb themselves if the bike was properly geared. I am looking to modernize the drivetrain and I am fairly dissappointed in the starting point, which is making everything a bit more challenging. That's the fun of it though right?

So here is my starting point
-11-40t Sunrace 9 Speed Cassette
-SRAM X4 derailleur and shifter
-some no name 145mm square taper 3 peice crank with a 104 BCD
-32t chainring
-square taper 100mmx151mm BB

My original plan
-I have a microshift acolyte rear clutched derailleur to toss on. This handles the 40 tooth better than the X4. Works great.
-I want to decrease the size of front chainring, but of course I am limited to 30t being a 104BCD crank. Ideally I would want a nicer 2 peice crank with a direct mount chainring that works with a 100mm BB shell with a crankarm length less than or equal to 140mm. This doesnt seem to exist.
-The chainline is terrible, neutral chain is sitting at ~gear 7 of 9. I would want to bring in the chainline about 13mm to have it neutral in 4th to prevent backpedal drop in 1st, and reduce drag.

New plan
-Use the acolyte derailleur
-Keep the same crank, but purchase a special 104BCD 26 tooth chainring that spaces the system inbound by about 8mm, then use 4mm chainring spacers to move the chainline about 12mm inbound. I wouldnt call this the perfect solution, but a manageable one.


Are there other options? Narrower square taper BB, I'm unfamiliar with sizing a square taper? Isis spline BB and new crank with direct mount chainring?

Any recommendations are greatly appreciated.

Thanks

 


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