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Disc Brake Tolerances - specs?

Posted: Mon Jun 11, 2018 11:06 am
by brackc
bit of a strange question, but does actually anyone know the tolerances between the brake pad and the rotor for the various disc groupsets?
Most interested in if the new Shimano Ultegra R8000 groupset runs closer to the rotor than the old RS685/785, but I haven't read anything in the reviews about this being the case (or not being the case), so does anyone have the actual specifications on this?

reason for asking is the smaller that pad-rotor gap the higher the likelihood the disc will rub on the pads if anything is slightly off.

Re: Disc Brake Tolerances - specs?

Posted: Mon Jun 11, 2018 11:47 am
by corky
This is the inherent fault with all current hydraulic road disc brake systems........until they design a method of retracting the pistons further away and thus the pads away from the rotor, brake rub will always be a problem......the magnitude of which depends upon your own tolerance(pun intended) to the shim shim shim sound.

All setups currently rely on the deformation of square shouldered seals that will reconform to their natural shape once the pressure of the hydraulic fluid has been released by releasing the brake levers. This seems like an easy no maintenance low weight solution but does not allow a sufficient pad rotor gap in my opinion.

Re: Disc Brake Tolerances - specs?

Posted: Mon Jun 11, 2018 11:47 am
by Weenie

Re: Disc Brake Tolerances - specs?

Posted: Mon Jun 11, 2018 12:54 pm
by ParisCarbon
Then throw in the variable of the disc not being in the same place on the wheel... I have 2 sets of wheels on my CX bike, both DT SWISS... I needed to put a pedal washer between the bearing and dustcap to add an offset to realign the disc down the middle... frustrating...

Re: Disc Brake Tolerances - specs?

Posted: Mon Jun 11, 2018 2:23 pm
by silvalis
November bikes sells rotor washers to shim multiple sets

It's possible to get good rotor clearance with careful bleeding.

Re: Disc Brake Tolerances - specs?

Posted: Mon Jun 11, 2018 2:43 pm
by ParisCarbon
silvalis wrote:
Mon Jun 11, 2018 2:23 pm
November bikes sells rotor washers to shim multiple sets

It's possible to get good rotor clearance with careful bleeding.
Problem with mine was the rotor was too far outboard, and really close to the seatstay (Stevens Super Presitige Post mount) so I had to do the washer deal to force alignment to the driveside slightly...

Re: Disc Brake Tolerances - specs?

Posted: Mon Jun 11, 2018 5:19 pm
by Andres
There are, and most will have something along the lines of what Sram has here on page 67. There should be enough movement in the mount to compensate for what you're referring to, is that not the case?

Re: Disc Brake Tolerances - specs?

Posted: Mon Jun 11, 2018 5:29 pm
by ParisCarbon
There is available movement in the brake itself to move it, but the rotor itself was probably less than a mm from the actual chainstay.. any hard flexing would probably cause the rotor to hit the frame (especially getting smashed around in cross)

Re: Disc Brake Tolerances - specs?

Posted: Mon Jun 11, 2018 8:36 pm
by TobinHatesYou
My SRAM HRD calipers give maybe a half millimeter of clearance on either side of the rotor and never get brake rub. If you do, true your rotors and align your calipers properly.

Re: Disc Brake Tolerances - specs?

Posted: Mon Jun 11, 2018 9:33 pm
by jfranci3
If your caliper is centered (loosen bolts, pull brake handle a few times, tighten caliper while pulled) and your wheel is fully tightened, then you may need to shim the rotor. I know there are 6-bolt shims from a few sources. For centerlock/afs, I've had to pull the washer off another centerlock hub.

Re: Disc Brake Tolerances - specs?

Posted: Mon Jun 11, 2018 9:43 pm
by jeanjacques
TobinHatesYou wrote:
Mon Jun 11, 2018 8:36 pm
My SRAM HRD calipers give maybe a half millimeter of clearance on either side of the rotor
Half milimeter ? Sound a lot. My Sram Red no hrd (same caliper) it's like 1/3 milimeter or less.

Re: Disc Brake Tolerances - specs?

Posted: Mon Jun 11, 2018 10:01 pm
by ParisCarbon
Hmm I'll look into the shifting caliper... My DT Swiss38 carbon tubs have the rotor well inside the seatstay while the clinchers R32 splines ae shifted... DT Swiss said this was entirely normal because they are different hubs..

A

Posted: Mon Jun 11, 2018 10:02 pm
by Delorre
TobinHatesYou wrote:
Mon Jun 11, 2018 8:36 pm
My SRAM HRD calipers give maybe a half millimeter of clearance on either side of the rotor and never get brake rub. If you do, true your rotors and align your calipers properly.
I can only squeeze a business card between rotors and pads (DA, not Sram), so max 0.2mm, but no rub 99,9% of the time.

Re: Disc Brake Tolerances - specs?

Posted: Wed Jun 13, 2018 10:56 am
by wheelsONfire

Re: Disc Brake Tolerances - specs?

Posted: Wed Jun 13, 2018 1:05 pm
by mattr
ParisCarbon wrote:
Mon Jun 11, 2018 5:29 pm
but the rotor itself was probably less than a mm from the actual chainstay.. any hard flexing would probably cause the rotor to hit the frame (especially getting smashed around in cross)
Some of the DH bikes i've worked on have less clearance than that. Not seeing any rub on those either. Even with all the slop in pivots and ~10" of travel......... i doubt you could get your rotor to touch the frame unless you actually bent it. Or the hub bearings failed.

Re: Disc Brake Tolerances - specs?

Posted: Thu Jun 21, 2018 7:25 am
by brackc
dre_lo82 wrote:
Mon Jun 11, 2018 5:19 pm
There are, and most will have something along the lines of what Sram has here on page 67. There should be enough movement in the mount to compensate for what you're referring to, is that not the case?
unfortunately those specs don't include pad return distance which is what I was after...
I was a bit curious if anyone had done the measurements to see if any company has greater clearance between pads/rotor or if it's changed with the updated shimano groupset, but it doesn't look like that's the case.

Re: Disc Brake Tolerances - specs?

Posted: Thu Jun 21, 2018 7:25 am
by Weenie