Why disc rotors are so freakin close to frame ?

Discuss light weight issues concerning road bikes & parts.
stormur
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by stormur

Noticed on few frames, specially rear; if brake post mount tabs are on chainstay not seatstay.

Doesn't matter 6bolts/centerlock... but no, on centerlock with 6bolts adaptor it is not to close, rotor literally touch frame.

there's 2 possibilities IMO , 1st is consistent across various brands bad design or poor build accuracy , or 2nd: they design frames for certain wheelsets which have "narrower hubs" ( I mean rotors mount pushed more away of frame than mine /fulcrum & dt swiss /.

Rotors I checked are Sram, Shimano, Magura. Sram Centerline CL is most "tight clearance" friendly. Shimano ( having narrowest rotors !) most unfriendly...

Does anyone have same expeirence, or I just hit "exceptional" cases only ?
Go to Heaven for the climate, Hell for the company.
Mark Twain


I can be wrong, and have plenty of examples for that ;)

by Weenie


joejack951
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by joejack951

What size rotors? If bigger than 140/160mm perhaps the frame is only designed for one of those smaller sizes.

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kkibbler
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by kkibbler

joejack951 wrote:What size rotors? If bigger than 140/160mm perhaps the frame is only designed for one of those smaller sizes.

If that were the case the calipers shouldn't fit the rotor either. /shrug

/donthaveadiscbike

joejack951
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by joejack951

About 2.5mm clearance here, 140mm rotor:

ImageShimano RT99 rotor, Bitex hub, Hongfu FM-079-F frame by joe jackson, on Flickr

Yes, I know. This is a flat mount frame not post mount like the OP mentions.
Last edited by joejack951 on Sat Feb 11, 2017 6:21 am, edited 1 time in total.

joejack951
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by joejack951

kkibbler wrote:
joejack951 wrote:What size rotors? If bigger than 140/160mm perhaps the frame is only designed for one of those smaller sizes.

If that were the case the calipers shouldn't fit the rotor either. /shrug

/donthaveadiscbike


Every disc brake caliper I've had my hands on (which to be honest is only Avid BB7 and TRP HY/RD and Spyre) has come with either multiple brackets or a reversible bracket to fit different size rotors. The caliper is typically 'adjustable' for various rotor sizes. That doesn't mean the frame (or fork) vendor designed their parts to accept all of those sizes.

stormur
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by stormur

wasn't precise enough.... look at joejack951 image, now move rotor outward so much that it touches brake mount on the frame, or space is 0-0.2-0.5mm . all sizes of rotors as "designed". zero adapters.
Go to Heaven for the climate, Hell for the company.
Mark Twain


I can be wrong, and have plenty of examples for that ;)

mattr
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by mattr

They need to be fairly close so the caliper doesn't move around when you brake. Most of my MTBs have a similar clearance. Even have one where the rivets between disc and carrier touched the caliper mount. (Don't use that combination any more).

If it's only the cl/6 bolt adaptor that gives you the problem. I'm not surprised. Not really much room for an adaptor there.......

stormur
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by stormur

can't see relation between braking and caliper movement. braking force direction is obvious here, and 1 plane only.

with adaptor rotor is nearly bent by caliper mount, on cl space is ... no there's no space; about 1-2 newspaper pages thickness ;) , and assuming it's Sram rotor, Shimano won't rotate at all ( it's thinner rotor , but thicker overall ) . Mostly calpiers are at the outward limit of adjustment. All measurements taken without caliper, so it's only wheel-rotor-frame relation.

Surprisingly this phenomenon doesn't exist on frames where brake is mounted on seatstay, only chainstay brake postioned frames are affected.

Q is , are hubs with rotors more inwards than other's ???
Go to Heaven for the climate, Hell for the company.
Mark Twain


I can be wrong, and have plenty of examples for that ;)

jeffy
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by jeffy

can cause issues on some direct drive trainers as well.

stormur
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by stormur

Another thought,

I installed other Fulcrum, from 650b bike , originally 6bolts : perfect clearance :) BUT wheels is 10spd (MTB), same OLD(135) . Now there's distance I'd like to see ! So... 11spd issue ?
Go to Heaven for the climate, Hell for the company.
Mark Twain


I can be wrong, and have plenty of examples for that ;)

joejack951
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Location: Wilmington, DE

by joejack951

You have yet to mention which hub(s) or frame. You also haven't posted any pictures. Something definitely sounds off with your setup and perhaps it is just an oddball hub. Or maybe the hub has been respaced by someone to move it closer to the non-drive side? All we can is guess though because you have provided very little information.

stormur
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by stormur

it's realy so hard to imagine rotor rubbing brake tab ? ;) I know something is wrong, that was reson of asking... If someone is changing anything in my stuff is only manufacturer ... or me :)

Nevermind.
Found it. It took just 3 hours :)

Issue was caused by specific hub: DT Swiss 3pawl type ( R23, R24 DB ). OLD of those is not certainly 135, rather 133.8; difference on NDS ( Center to DS keeps dimensions ). Weird. Mine 2 wheelsets have same issue, and 1 not mine. Same measurements on all of it.

DT240 type ( ratchett, Dicut ) seems to be fine, Campagnolo/ Fulcrum CL/ 6 bolts too ( CL->6bolts adaptor changes everything, but originally 6b is fine ). However Fulcrum on front is closer to brake tabs than any other hub.( still tolerance is fine there, but again CL to 6b make it way to close ).

But still have impression that 6bolts hubs have rotors bit more inward in comparison to CL. Have to measure it some day.. maybe it is just illusion (?). Did someone check it ?
Go to Heaven for the climate, Hell for the company.
Mark Twain


I can be wrong, and have plenty of examples for that ;)

mattr
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by mattr

There's no standard offset for discs. That's why everyone's are (slightly) different. And why you can get shims.

There is a range of offsets stated for shimano discs/calipers though. I would suspect most manufacturers follow that. But when you get to opposing extremes, you get clashes.

mattr
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by mattr

stormur wrote:can't see relation between braking and caliper movement. braking force direction is obvious here, and 1 plane only.
One plane? Go back and look at the forces in three dimensions. Then the geometry of the caliper and mounting faces.

by Weenie


TheKaiser
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by TheKaiser

mattr wrote:There's no standard offset for discs. That's why everyone's are (slightly) different. And why you can get shims.

There is a range of offsets stated for shimano discs/calipers though. I would suspect most manufacturers follow that. But when you get to opposing extremes, you get clashes.


Exactly right, and this is part of the reason why pro peloton wheel changes with disc brakes could be a real mess. Within a single team, they have the potential to standardize the tolerances on each of their bikes and wheelsets, but with a neutral support wheel...no way. Even with standardized parts within a team, the clearances are simply too tight between a rotor and pads to simply rely on the same hub rotor combo, as a slightly undersized spacer, hub shell mounting face, or an out of plane locknut on a QR wheel will throw things into disarray unless you check each and every set.

For an average rider it's no biggy, but can you imagine being a front runner at Paris-Roubaix, getting a flat, getting a wheel change, and then hearing your brakes rubbing and grinding once you think you are back in the hunt...that would suck.

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