Do you think this none drive side crankarm will come off ?

Discuss light weight issues concerning road bikes & parts.
coolmingli
Posts: 35
Joined: Fri Feb 03, 2012 9:10 am

by coolmingli

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.

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

coolmingli
Posts: 35
Joined: Fri Feb 03, 2012 9:10 am

by coolmingli

The preload cap did tread into the spindle with 5-6 turns.

Svetty
Posts: 493
Joined: Thu Mar 26, 2009 11:06 pm
Location: Yorkshire - God's Own Country

by Svetty


coolmingli
Posts: 35
Joined: Fri Feb 03, 2012 9:10 am

by coolmingli

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.

DamonRinard
in the industry
Posts: 227
Joined: Fri Apr 29, 2011 8:32 pm

by DamonRinard

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.
Damon Rinard
Engineering Manager, Road Bikes
Cycling Sports Group, Cannondale
Ex-Kestrel, ex-Velomax, ex-Trek, ex-Cervelo

eric
Posts: 2196
Joined: Tue Nov 11, 2003 9:47 pm
Location: Santa Cruz, California, USA
Contact:

by eric


DamonRinard
in the industry
Posts: 227
Joined: Fri Apr 29, 2011 8:32 pm

by DamonRinard

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

Image
Damon Rinard
Engineering Manager, Road Bikes
Cycling Sports Group, Cannondale
Ex-Kestrel, ex-Velomax, ex-Trek, ex-Cervelo

coolmingli
Posts: 35
Joined: Fri Feb 03, 2012 9:10 am

by coolmingli

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?

eric
Posts: 2196
Joined: Tue Nov 11, 2003 9:47 pm
Location: Santa Cruz, California, USA
Contact:

by eric

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.

User avatar
HammerTime2
Posts: 5432
Joined: Thu May 04, 2006 4:43 pm
Location: Wherever there's a mountain beckoning to be climbed

by HammerTime2

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.

Svetty
Posts: 493
Joined: Thu Mar 26, 2009 11:06 pm
Location: Yorkshire - God's Own Country

by Svetty

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.

eric
Posts: 2196
Joined: Tue Nov 11, 2003 9:47 pm
Location: Santa Cruz, California, USA
Contact:

by eric

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.

Svetty
Posts: 493
Joined: Thu Mar 26, 2009 11:06 pm
Location: Yorkshire - God's Own Country

by Svetty

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.

eric
Posts: 2196
Joined: Tue Nov 11, 2003 9:47 pm
Location: Santa Cruz, California, USA
Contact:

by eric

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.

DamonRinard
in the industry
Posts: 227
Joined: Fri Apr 29, 2011 8:32 pm

by DamonRinard

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,
Damon Rinard
Engineering Manager, Road Bikes
Cycling Sports Group, Cannondale
Ex-Kestrel, ex-Velomax, ex-Trek, ex-Cervelo

Post Reply
  • Similar Topics
    Replies
    Views
    Last post