Hollowgram: 1x to 2x self made upgrade

Discuss light weight issues concerning road bikes & parts.
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alcatraz
Posts: 1240
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Hi WW...

This could be the craziest idea I ever had. I'm looking to have a 48/30 crank for my road climbing bike while keeping things light. I've been searching for a 104bcd spider ever since. The crank would end up at around 30gr spider 30gr small ring 85gr big ring 5gr bolts. 150gr. Not much lighter than my opi 10 arm 50/34 spidering.

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After finding this pic from extralite it gave me the idea of making myself a 2x chainring setup from a 1x 30t spidering. What do you think of that idea? One problem is the chainline. There are two kinds of spiderings with slightly different chanlines. Maybe one can mimic a 2x drivetrain.

The DIY would be to get any light 48t chainring with arms that can reach into the 30t ring then drill and tap some threads into one of the chanrings and screw them together with an appropriately sized spacer. M6 or M8 titanium/alloy bolts could maybe work, or perhaps common chainring bolts and tap those threads in the 30t ring and use a 48t 104bcd big ring.

A 30t spiderring is 50gr. 4 bolts and spacers are 5gr. 48t ring is 85gr. 140gr. Not much weight saved :lol: but I don't need an expensive and rare to find 104bcd hollowgram spider.

Any comments or ideas? Thank you for reading...

/a

morganb
Posts: 587
Joined: Wed Mar 15, 2017 5:30 pm

by morganb

You aren't going to be able to shift off the 30T, its a chain retaining profile and not shaped to derail.

by Weenie


alcatraz
Posts: 1240
Joined: Mon Aug 29, 2016 11:19 am

by alcatraz

Good point. Thanks Morganb.

Wouldn't the chain touch the big chainring's ramps before it is influenced by the small ring tooth design and simply lift off?

Hmm...

/a

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