Disc Rotors - various questions

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robeambro
Posts: 1829
Joined: Sat Jul 07, 2018 6:21 pm

by robeambro

Hi all

I won't write too much. TL;DR is, I have a bike with two wheelsets (same DT Swiss hubs). Wheelset A has relatively worn Shimano XTR rotors. Wheelset B has new SRAM Centerline X rotors.

The bike was set up in the shop with wheelset A. Currently, fitting wheelset B is a challenge, as SRAM rotors are pretty much perma-rubbing on the pads (also due to a slightly lazy piston, but this causes no issue with wheelset A). The same rotors rub equally when fitted onto wheelset A, so this is clearly not due to hubs.

My cursory research suggests SRAM rotors are marginally thicker, and of course they're also new, as opposed to the Shimano ones.

Other than the thickness, is this is a brake bleed issue, and if I were to rebleed the brakes with the SRAM rotors, would I solve the issue or do I risk having poor performance with the Shimano rotors? I wouldn't want to fix one issue only to create another. Just trying to understand whether I should just buy another set of XTR rotors or go with another brake bleed.

by Weenie


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TheDoctor
Posts: 195
Joined: Sun Dec 17, 2017 9:56 pm

by TheDoctor

Is the wheelset with the sram rotors rubbing on the in- or outside pad? I'm assuming it is not rubbing on both? The thickness difference with xtr should not be that much.
Assuming it's rubbing only on one side: personally I'd adjust the calipers to align with the wheelset with the most outward rotor, and then shim the wheelset with the most inward rotor to match the caliper alignment. That is the easiest way to deal with slight differences in alignment.

CampagYOLO
Posts: 705
Joined: Thu May 06, 2021 3:58 pm

by CampagYOLO

robeambro wrote:
Tue Mar 28, 2023 2:12 pm
Hi all

I won't write too much. TL;DR is, I have a bike with two wheelsets (same DT Swiss hubs). Wheelset A has relatively worn Shimano XTR rotors. Wheelset B has new SRAM Centerline X rotors.

The bike was set up in the shop with wheelset A. Currently, fitting wheelset B is a challenge, as SRAM rotors are pretty much perma-rubbing on the pads (also due to a slightly lazy piston, but this causes no issue with wheelset A). The same rotors rub equally when fitted onto wheelset A, so this is clearly not due to hubs.

My cursory research suggests SRAM rotors are marginally thicker, and of course they're also new, as opposed to the Shimano ones.

Other than the thickness, is this is a brake bleed issue, and if I were to rebleed the brakes with the SRAM rotors, would I solve the issue or do I risk having poor performance with the Shimano rotors? I wouldn't want to fix one issue only to create another. Just trying to understand whether I should just buy another set of XTR rotors or go with another brake bleed.
You never set up a bike with the rotors or pads in place, don't want brake fluid on them. Likewise when you bleed the brakes, that's why all bleed kits have a bleed block you put in place of the pads.

I'm with the above poster, more likely to be an issue with the spacing being slightly different between wheelsets.
Last edited by CampagYOLO on Tue Mar 28, 2023 5:18 pm, edited 1 time in total.

bmCube
Posts: 122
Joined: Wed Jan 05, 2011 8:37 pm

by bmCube

Also, when you install the wheels with sram rotors, do you reset the pistons (aka push the pistons back in the calipers), then pull the levers multiple times, so the pistons set them on the sram rotors? Maybe you have luck and don't need to realign the calipers.....

ooo
Posts: 1590
Joined: Sat May 21, 2016 12:59 pm

by ooo

instead of
a-front=worn-xtr, a-rear=worn-xtr
b-front=sram-clx, b-rear=sram-clx
do this:
a-front=sram-clx, a-rear=worn-xtr
b-front=sram-clx, b-rear=worn-xtr
'

robeambro
Posts: 1829
Joined: Sat Jul 07, 2018 6:21 pm

by robeambro

Thanks all. The SRAM rotor rubs on both sides. I've been doing further tests and this only happens at the front where there's the lazy piston, so I am inclined to think that the lazy piston plus slightly greater thickness of SRAM rotors (0.2mm higher TAM - thickness as measured, trademark by me) don't play well together. Ugh.

by Weenie


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TobinHatesYou
Posts: 12455
Joined: Mon Jul 24, 2017 12:02 pm

by TobinHatesYou

Slight tangent, but some of my Centerlinex XR rotors measure nearly almost 1.85mm as advertised. Others measure 1.7mm when new. It's weird to me that this much variance is permitted.

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