disc brake caliper rubbing against spokes

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banditgp
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disc brake caliper rubbing against spokes

Postby banditgp » 2 Feb 2016, 1:02pm

hello all, first time on the forum, and i'm looking to see if anyone has encountered the same niggle that i am, and how they may have fixed it.
I've upgraded to a dynamo hub on my specialized awol and found that the brake caliper is now rubbing against the spokes of the front wheel. it's not a huge amount, it's more of an annoyance than a real problem atm.
(i have tried adjusting the caliper position)
As far as i can see I have 3 options;
change the caliper to a less chunky one
rebuild the wheel which may not actually change much and is probably the most expensive option as i've never done it before
switch from a 160 rotor to a 180 rotor which is the option I'm much preferring due to costs and ease but what's anyones thoughts of running a touring bike with 180 discs up front? With the tradition of the awol, most of the weight is up front anyway so it makes sense but i'm new to road orientated bikes running discs, hence the query.
Has anyone else come across a similar issue and are there any other options i may be missing?
thanks for your time

Brucey
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Re: disc brake caliper rubbing against spokes

Postby Brucey » 2 Feb 2016, 1:51pm

are the spokes properly braced at the crossings?

If so, your #1 option is to respace the disc from the hub a little, and move the caliper to suit. You can buy disc mount shims to permit this on 6-bolt discs. Be careful though; the disc or its mounting bolts may foul something if you move them far.

Having said that, it is possible that the RH pad in your caliper is worn or not adjusted correctly; it might help if you say what kind of brake you have and if the pads are new or worn.

BTW if the spokes are not properly braced at the crossings, (which also means that they will 'twang' in a resonant fashion) they are more likely to foul the caliper IME.

cheers
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reohn2
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Re: disc brake caliper rubbing against spokes

Postby reohn2 » 2 Feb 2016, 2:17pm

If the calliper is juussttt catching the spokes,and there's enough clearance outboard between rotor and fork leg,six 2mm washers between hub and rotor* and two 2mm washers between calliper adapter and fork mount,moves everything out board 2mm,which could/should be enough.
If the calliper is a dual pad action,TRP Spyre(?),the calliper can be run with the rotor slightly off centre to give an extra 1mm or so.

*you may need to file a flat on the outer edge of the washers as they may juusstt foul the static part of the hub,though I'm not sure if that's the case with your particular hub dynamo.
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banditgp
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Re: disc brake caliper rubbing against spokes

Postby banditgp » 2 Feb 2016, 2:35pm

thanks for the replies, as far as i can tell the spokes look correctly braced, and no the pads aren't worn, it's a new bike with only about 400 miles on it.
The caliper is a TRP spyre, Exposure Lights dynamo hub
i'll start with the disc mount shims which sounds like it should do the job
cheers

any thoughts on the 180 disc option? there was noticeable benefit when i moved from a 160 to 180 disc on a mtb which is why my first thought was the same option here?

reohn2
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Re: disc brake caliper rubbing against spokes

Postby reohn2 » 2 Feb 2016, 3:43pm

banditgp wrote:........any thoughts on the 180 disc option? there was noticeable benefit when i moved from a 160 to 180 disc on a mtb which is why my first thought was the same option here?


The fork may not be rated for a 180 rotor,and so could invalidate you're warranty should anything go wrong.
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foxyrider
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Re: disc brake caliper rubbing against spokes

Postby foxyrider » 2 Feb 2016, 4:43pm

reohn2 wrote:
banditgp wrote:........any thoughts on the 180 disc option? there was noticeable benefit when i moved from a 160 to 180 disc on a mtb which is why my first thought was the same option here?


The fork may not be rated for a 180 rotor,and so could invalidate you're warranty should anything go wrong.


That said, you probably will find an improvement - i have with my HyRd's
Convention? what's that then?
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rmurphy195
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Re: disc brake caliper rubbing against spokes

Postby rmurphy195 » 2 Feb 2016, 7:10pm

banditgp wrote:thanks for the replies, as far as i can tell the spokes look correctly braced, and no the pads aren't worn, it's a new bike with only about 400 miles on it.
The caliper is a TRP spyre, Exposure Lights dynamo hub
i'll start with the disc mount shims which sounds like it should do the job
cheers

any thoughts on the 180 disc option? there was noticeable benefit when i moved from a 160 to 180 disc on a mtb which is why my first thought was the same option here?


I have the spyres, with the 160mm rotors, Before you try shims,try moving the caliper sideways a bit away from the wheel. Also note that the pads can be individually adjusted with a 3mm allen key - so you might be able to move the caliper sideways to clear the spokes, then re-centralise the pads using the adjusters. Also use the videos that Spyre publish on youtube, especially the one about curing judder, just in case you end up creating that particular problem! https://www.youtube.com/watch?v=1T2RLgQoyvs
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Gattonero
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Re: disc brake caliper rubbing against spokes

Postby Gattonero » 2 Feb 2016, 7:24pm

banditgp wrote:...
The caliper is a TRP spyre,...


Easy-peasy then.

The caliper has pad adjusters on both sides. Unscrew fully both of them.
Unscrew the PM adapter bolts (the ones that make you move the caliper left/right), just what's enough to make the caliper move free sideways.
Now give only one turn clockwise to the pad facing the hub, and give as many turns as it needs the outer pad adjuster to lock the caliper on the rotor (pads fully closed).
Close the PM adapter bolts, just to make it steady, 1-2-1-2 will avoid the caliper moving.
Last thing: undo 1/2 turn or as much as it needs to both pads adjusters to get the rotor free from drag.

This way you're setting the caliper towards the left, just enough to clear the Lh spokes of the wheel
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Brucey
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Re: disc brake caliper rubbing against spokes

Postby Brucey » 2 Feb 2016, 11:49pm

often not a good idea to shuffle a caliper sideways like that; if the disc is over to one side of the caliper body slot, with some models of brake the brake pad can try to 'escape' on the side with the larger gap once the pads are worn. This can cause brake seizure (if the pad jams in the gap) or no brakes (if the pad breaks the retaining pin and escapes).

Nearly all brake pads are retained in use (i.e. vs the brake loads which can be of the order of ~300kg on each pad) by the pad backing bearing against the caliper body recess; any retaining pin is there as a backup only, not to resist braking loads on a routine basis. A setup where the disc is to one side of the caliper body gap will be fine when the pads are new, but can be pretty dangerous once the pads are worn.

If in doubt, it is a good policy to keep the disc centred in the caliper body slot wherever possible.

cheers
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Gattonero
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Re: disc brake caliper rubbing against spokes

Postby Gattonero » 3 Feb 2016, 8:11am

The Spyre has both pads moving, and pads wear has to always be checked, I do not see a big problem. One has to be very careless to keep on riding while hearing the noise of grinding metal, if that happens
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...

yostumpy
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Re: disc brake caliper rubbing against spokes

Postby yostumpy » 3 Feb 2016, 10:02am

out of interest, which dynohub did you go for, and was it 6 bolt or centrelock?

Brucey
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Re: disc brake caliper rubbing against spokes

Postby Brucey » 3 Feb 2016, 10:08am

Gattonero wrote:The Spyre has both pads moving, and pads wear has to always be checked, I do not see a big problem. One has to be very careless to keep on riding while hearing the noise of grinding metal, if that happens


my point is that you can end up in a pickle of the sort described without there being such noises beforehand.

There are very many variables which affect if this happens or not, because pad backings vary in thickness and so do discs. Some brake systems (using recommended matched parts) are only 'safe' if the disc is exactly centred in the caliper slot and the pad wear is uniform on both sides. Quite a lot of brake manufacturer's specifications do not allow you to wear more than about half the lining thickness away before they deem pad replacement necessary and this is one reason why.

Arguably you are in a cleft stick here; if the caliper slot is wide enough to allow much adjustment, it probably isn't safe to use it for the reasons I have described. If it is much narrower than that, it probably isn't worth doing anyway.

cheers
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banditgp
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Re: disc brake caliper rubbing against spokes

Postby banditgp » 3 Feb 2016, 11:53am

Thanks again for all your replies, It's a 6-bolt PD-8 hub. I had a bit of a tinker with the calipers last night an it needs more than just an adjustment there. If I move the caliper as far as it can go to clear the spokes it's then bang up against the rotor so it definately needs "something else". I've ordered a rotor spacer as I reckon the suggestion of a rotor spacer then a washer before the fork mount (cheers reohn2) is definately a logical place to start. I've also ordered a caliper mount to try the 180 disc as I have spare rotors from my mtb so that's another fairly easy trial. I did ping off an email to specialized and my local spec lbs to get their take on the 180 rotor as that cautionary note is something i hadn't considered.

[updated] yep, lbs confirmed upgrade to 180 is not a problem and does not affect the warranty, good times !!
Last edited by banditgp on 3 Feb 2016, 1:56pm, edited 1 time in total.

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Gattonero
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Re: disc brake caliper rubbing against spokes

Postby Gattonero » 3 Feb 2016, 1:25pm

Brucey wrote:
Gattonero wrote:The Spyre has both pads moving, and pads wear has to always be checked, I do not see a big problem. One has to be very careless to keep on riding while hearing the noise of grinding metal, if that happens


my point is that you can end up in a pickle of the sort described without there being such noises beforehand.

There are very many variables which affect if this happens or not, because pad backings vary in thickness and so do discs. Some brake systems (using recommended matched parts) are only 'safe' if the disc is exactly centred in the caliper slot and the pad wear is uniform on both sides. Quite a lot of brake manufacturer's specifications do not allow you to wear more than about half the lining thickness away before they deem pad replacement necessary and this is one reason why.

Arguably you are in a cleft stick here; if the caliper slot is wide enough to allow much adjustment, it probably isn't safe to use it for the reasons I have described. If it is much narrower than that, it probably isn't worth doing anyway.

cheers


We're not talking of moving the caliper a lot, we're talking 1mm or less. If you look carefully, most of mechanical disk-brakes have a tolerance of the pad's resting position that is already higher than that.
As long as the pads do touch the rotor at the same time, their actuation has no noticeable error if we're talking of such small offset (<1mm). Also ,the rotor is meant to flex that little, would the single-pad disk brakes be truly unsafe then? I think that such adjustment is very safe and nothing to worry about.
It is by riding a bicycle that you learn the contours of a country best,
since you have to sweat up the hills and coast down them.
Thus you remember them as they actually are...

Brucey
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Re: disc brake caliper rubbing against spokes

Postby Brucey » 3 Feb 2016, 7:08pm

Gattonero wrote: We're not talking of moving the caliper a lot, we're talking 1mm or less.....


OK suppose you can move the disc 1mm sideways from the centre position. This implies that the caliper slot is about 4mm wide (for a 2mm thickness disc) and now you have a gap of 2mm on the other side.

Sorry, that is not 'safe' because the pad (almost any part worn pad) can go through that gap and when it does it'll have a pretty good go at killing you.

If the caliper slot is (say) 3mm instead then you can shuffle the caliper 0.5mm from the centre position which is 'safer' (not 'safe', pad backings are often ~1mm thickness...) but even if you do that it is hardly worth doing in terms of the extra clearance you might get vs what you need. If the caliper touches the spokes when you are going in a straight line you need at least 1mm (and probably 2mm) more clearance if there is to be no touching when riding out of the saddle.

...I think that such adjustment is very safe and nothing to worry about.


I think you might need to have another think... :wink:

Inexpensive six-bolt spacers (in stock at all good bike shops ) are designed for safely resolving this exact issue.

cheers
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