Time for another kids project. Carbon, 650b, mtn bike.

[xnavalav8r]

No unsolicited advertising please. Thanks

[gravity]

This is definitely the coolest kids bike I have ever seen! Your boy must be super stoked!

[xnavalav8r]

Updating to a Middleburn RS7 crank with 27/40 chainrings. I unfortunately could not get the crank in any color other than silver. So, it will lose some style points.

[xnavalav8r]

Update: Bike had its first really serious offroad thrashing yesterday. The shifting, which has been amazing on the bike path and park trails, was TERRIBLE!!!! The rear derailleur just can't take the bouncing and bumping of offroad riding. 5 dropped chains in an hour. It was a nightmare. My son was really frustrated. Back to the drawing board on drivetrain. We're likely going to switch to a 1x10/11 setup with a 30t chainring and a wide-ratio cassette using a clutch-type derailleur.

[whilgenberg]

Have you tried a different chainring set? A 27/40 combo requires a huge difference in chain length that I am not sure a Di2 derailleur can handle. In fact I don't know if any derailleurs other than extra long cage derailleurs for triples would be able to handle that capacity. That might be the issue that you're having with the chain dropping.

[Raineman]

Did you increase the derailluer cage tension?

[xnavalav8r]

Whilgenberg: We tried other chainring combos. But we couldn't get a low enough gear. I think you are probably right though.

Raineman: The rear derailleur cage tension was as high as I could make it. I considered an aftermarket spring but stuck with the stock spring in the max-tension position, then used an extra long b-tension screw.

I think this concept is a bust for this particular application. I may put the setup on my wife's bike. She doesn't do any racing.

[xnavalav8r]

Worked some ebay magic and switched to a 1x11 di2 setup. No more dropped chains.

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