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PostPosted: Sun Jul 07, 2013 6:03 am 
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Posts: 35
After switched to Rotor 3D and Praxis compact from 7950, my chain rubs inside large chainring, I add a 1mm spacer on the drive side, then add another 1mm spacer to the none drive side so I can have Symmetrical Q factor, everything is good, but my crank spindle doesn't stick out long enough, it only go thru 2/3 of the thickness of the none drive side crank arm. What do you guys think, I just don't want the arm come off during riding. The bottom bracket is Enduro Zero Ceramic.
I kinda regret now, should have kept my 7950, it was perfect.

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Last edited by coolmingli on Sun Jul 07, 2013 6:54 am, edited 1 time in total.

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Posted: Sun Jul 07, 2013 6:03 am 


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PostPosted: Sun Jul 07, 2013 6:07 am 
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The preload cap did tread into the spindle with 5-6 turns.


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PostPosted: Sun Jul 07, 2013 8:50 am 
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viewtopic.php?f=3&t=116422


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PostPosted: Sun Jul 07, 2013 9:22 am 
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I wish I saw this post before I sold my 7950, the chainrings I have are the 50/34, wonder if I change to 50/36 will get rid of the rubbing.


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PostPosted: Sun Jul 07, 2013 11:42 am 
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Hi cool,

Why not move the two chain rings ~1mm apart? Use 5 tiny spacers, one at each mounting bolt.

Then remove the axle spacers and enjoy rub-free riding.

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Damon Rinard
Senior Advanced R&D Engineer at Vroomen.White.Design
http://www.cervelo.com
http://www.bbright.net/


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PostPosted: Sun Jul 07, 2013 2:39 pm 
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Joined: Tue Nov 11, 2003 9:47 pm
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Location: Santa Cruz, California, USA
http://www.ebikestop.com/chainring_chai ... %29469.php


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PostPosted: Sun Jul 07, 2013 5:16 pm 
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eric wrote:
http://www.ebikestop.com/chainring_chainring_spacers%29%29469.php" onclick="window.open(this.href);return false;


Perfect! Thanks eric. I'd suggest the 0.6 mm spacers first.

http://www.ebikestop.com/06mm_alloy_cha ... CR1229.php

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Damon Rinard
Senior Advanced R&D Engineer at Vroomen.White.Design
http://www.cervelo.com
http://www.bbright.net/


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PostPosted: Sun Jul 07, 2013 7:32 pm 
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I am not going to pay $60 buy 5 washers, kinda skeptical, don't even know it will work or not.
The rubbing was the problem, the new problem is in my post title.
I just don't have faith the none drive side crank arm will stay in place, but even if I take out the washer, the Rotor 3D spindle is no gonna go all the way thru to the edge of the NDS arm. Does anyone know how much of the spindle length needs to go into the NDS arm in order to be safe to ride?


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PostPosted: Sun Jul 07, 2013 8:55 pm 
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Buy 5 washers from your LBS. Should cost about $10 or so. They will address your original problem. Then you can undo your bodge job and allow the crank to work correctly.

I would not ride that. Having a crank break is no fun.


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PostPosted: Mon Jul 08, 2013 1:44 am 
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coolmingli wrote:
I am not going to pay $60 buy 5 washers ...
That's $11.95 for a bag of 20 spacers, not the price per spacer. That said, this does not constitute a recommendation as to your course of action.


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PostPosted: Wed Jul 10, 2013 2:54 pm 
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Problem with spacing the rings further apart is that the shifting will suffer and the chain could get stuck in between the rings if the gap is too large.


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PostPosted: Wed Jul 10, 2013 6:05 pm 
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When I added spacers (FSA rings on a Lightning crank), shifting improved. The rings were too close together, which is why I needed the spacers in the first place. There is no standard for the thickness of the spider, or chainring offset, or even the lateral positon of the spider.

I think the OP's new setup suffers from the same problem. He could take some measurements to see if that's actually the case.


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PostPosted: Thu Jul 11, 2013 1:56 pm 
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eric wrote:
When I added spacers (FSA rings on a Lightning crank), shifting improved. The rings were too close together, which is why I needed the spacers in the first place. There is no standard for the thickness of the spider, or chainring offset, or even the lateral positon of the spider.

I think the OP's new setup suffers from the same problem. He could take some measurements to see if that's actually the case.


Different rings, different set-up. the Praxis rings are precisely engineered to ensure shifting is spot-on. Regarding standards, there is a standard for the mid-line of the inter-ring space - 43.5mm.


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PostPosted: Thu Jul 11, 2013 6:40 pm 
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Yea, although I thought it was 45mm to the inner side of the big ring.

But that says nothing about the spacing between the rings, which is what I think the OP's problem is. When the spacing is too narrow the chain rubs on the inside of the big ring. On a 50/34 setup it's already close if not rubbing in the smallest cog. Losing even .5mm there will make a big difference.


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PostPosted: Fri Jul 12, 2013 1:14 am 
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Eric is right on with his advice. The symptoms point directly to the two rings being too close.

Here's a thought: don't buy the Spacers at first. Instead, cut some out of cardboard or thin metal, whatever you have. Give it a try first. If it works (99% sure it will), then buy the real spacers.

Cheers,

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Damon Rinard
Senior Advanced R&D Engineer at Vroomen.White.Design
http://www.cervelo.com
http://www.bbright.net/


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Posted: Fri Jul 12, 2013 1:14 am 


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