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Adjusting rim brake spacing for wear? (cantilever)

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Adjusting rim brake spacing for wear? (cantilever)

Old 04-14-22, 10:33 PM
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John Hawkinson
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Adjusting rim brake spacing for wear? (cantilever)

Hi. Tektro Oryx brakes (cantilever, yes? Not V? I think?) brakes on my touring bike.

I've always left the brake pad spacing on the "3 mm" option, which is what they came with and what the LBS has set the bike to after a tuneup involving pad replacement.
Usually when one wheel's brakes don't have good stopping force anymore (as I noticed this weekend when my front wheel got out of true and so I popped open the front brake and realized the rear brake was not adequate to stop the bike) and the barrel adjuster is maxed out, I just replace the brake pads, and look at them and wonder why there's so much pad left before running down to the wear line. Then I give up and move on.

Anyhow tonight I thought, "well, why don't I just advance the spacing on the pad and get more life out of it?" i.e. moving around the spacers and conical washers.
First I moved to the "4 mm" setting by moving the thin washer from outside the fork to adjacent to the pad. This was better but still left room for improvement.
Then I went to the "5 mm" setting by putting the washer back where it was before and swapping the 2mm and 4mm spacers. This seemed excellent at first, but after a test ride there was some rubbing of the rear wheel.
I dug up some spare washers from old worn out brake pads and went back to the "4 mm" setting plus doubling up the thin washer (I think it measured 0.8mm on my calipers? Did not write it down, my bad) and that seemed to be a good compromise. Maybe I should futz with the lateral true of the rear wheel.

Anyhow, I don't see anything in the literature (print or web) that suggests increasing the fork-to-pad spacing (decreasing the pad-to-rim spacing) is a normal maintenance task. Nobody seems to be explicit, but it seems like this spacing is intended as a set-it-and-forget it.

Am I wrong to be changing this spacing to get more life of my pads? And if so why?

Maybe I need barrel adjusters with more travel?

Thanks!
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Old 04-15-22, 04:51 AM
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If the barrel adjusters are maxed out and the pads still have life, why not just tighten the cable?
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Old 04-15-22, 05:21 AM
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Originally Posted by bboy314 View Post
If the barrel adjusters are maxed out and the pads still have life, why not just tighten the cable?
Great question. Of course the real answer is I didn't think about that.

But my experience is I get many years and sets of pads out of a set of brake cables, and that loosening and tightening the pinch bolt more than a few times leads to a freyed cable,
On the other hand, it's probably easier than messing around with swapping washers and spacers, and infinitely variably adjustable.

But it still leaves the real question: Is it normal to have to make this kind of adjustment over the life of a pad?
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Old 04-15-22, 06:14 AM
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Past the initial new pad setup, I never really have to mess with the pad spacing. If your cable is fraying when you adjust it, you might just be overtightening a little. I do like to use a simple straddle yoke without pinch bolts which makes it easier to just tighten the cable at the brake arm.
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Old 04-15-22, 06:29 AM
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I don't think the conical washer-and-spacer system is designed to be used to maintain pad-to-rim clearance as the pad wears. I think it's designed to help you adjust and tune your brake system from the onset...because different types of brakes (cantilever vs. linear pull) and different brake boss spacing exist in the market and exactly how the brake is configured can have a pretty large effect on performance.

For example, low profile cantilevers, like the Oryx brakes, usually respond well to a wider brake arm splay at rest. In other words, install the pads with the thickest spacers to the inside of the brake arm (which moves the pad closer to the rim, right?). This forces you to set the arms wider apart, which minimizes the loss of mechanical advantage that low profile cantilevers experience as they're actuated (pulled together). Your straddle cable will also generally sit lower with a straighter path between each arm (assuming you have the tire or fender clearance), which increases mechanical advantage.

The relatively small amount of pad wear over the life of the pads (in terms of dimensions you can measure) can well be taken up by the barrel adjuster up at the brake lever.
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Old 04-15-22, 07:00 AM
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Study this. Pop quiz tomorrow.

A real key to canti brake performance is maintaining the yoke angle of the straddle cable system. Most of the old canti brakes I see coming into the non-profit shop have an extremely acute angle at the straddle clamp, which I think comes from persistently tightening the brake cable to allow for pad wear, probably over many years and many pairs of shoes. I usually have to start from scratch, forget about the shoes, get the geometry of the calipers and straddle cable correct, then adjust shoes accordingly. Measurements depend on rim and brake boss widths.
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Old 04-15-22, 03:58 PM
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Originally Posted by bboy314 View Post
If the barrel adjusters are maxed out and the pads still have life, why not just tighten the cable?
Because as cantilever brake pads wear, they hit lower and lower on the rim until "OH CRAP!" they dive under the rim and NO MORE BRAKE!!! (Ask me how I know!)

Canti pads need to be set properly to hit the rim at the correct angle, achieve good leverage, avoid brake pad dive, prevent squeal, and make sure you aren't gonna slash that sidewall. Straddle cable length should be optimized for optimal leverage and braking power. Too long, not enough power, too short, too squishy.

Now if the OP actually means v-brakes, then (in an Emily Litella voice), "Never mind!" Set up still requires much of the above, but without the dire consequences. Many v-brakes require you just push the pad against the rim loose, make sure it's tangent and at the proper height, and tighten down the nut. Squeal was supposedly eliminated and toe wasn't necessary. (But we all know that isn't true, don't we!)
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Old 04-15-22, 04:00 PM
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I feel it should be a right of passage for EVERY bicycle mechanic to be able to master cantilever brake set up. Not for any particular reason, of course. Just to build proper character !
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Old 04-15-22, 04:00 PM
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Originally Posted by me
But my experience is I get many years and sets of pads out of a set of brake cables, and that loosening and tightening the pinch bolt more than a few times leads to a freyed cable,
Originally Posted by bboy314 View Post
Past the initial new pad setup, I never really have to mess with the pad spacing. If your cable is fraying when you adjust it, you might just be overtightening a little. I do like to use a simple straddle yoke without pinch bolts which makes it easier to just tighten the cable at the brake arm.
Wow, I was really unclear, I don't now why I wrote it the way I did, sorry. I don't actually have any meaningful experience tightening (or overtightening) my brake cables, and indeed I think I've only ever replaced my own brake cables once, although I guess I have replaced a seized pair of calipers too, and it was in doing the latter that I noted the brake cable looked pretty frayed on the brake after however many years (I forget when the LBS last replaced the brake cables, if ever). So it was really a theoretical concern. Perhaps it is unjustified!
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Old 04-15-22, 04:05 PM
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Originally Posted by LV2TNDM View Post
Now if the OP actually means v-brakes, then (in an Emily Litella voice), "Never mind!" Set up still requires much of the above, but without the dire consequences. Many v-brakes require you just push the pad against the rim loose, make sure it's tangent and at the proper height, and tighten down the nut. Squeal was supposedly eliminated and toe wasn't necessary. (But we all know that isn't true, don't we!)
The OP wasn't quite sure, hence the statement: "Tektro Oryx brakes (cantilever, yes? Not V? I think?)"

It seems unfathomable to me that Tektro's product page: www.tektro.com/products.php?p=48
doesn't say either "cantilever brake" or "V-brake" but alas:

992AG
DESCRIPTION
Brake - Cyclocross Collection
◆ Linear spring designed
◆ Dual micro tension adjusters

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Old 04-15-22, 04:11 PM
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Originally Posted by LV2TNDM View Post
I feel it should be a right of passage for EVERY bicycle mechanic to be able to master cantilever brake set up. Not for any particular reason, of course. Just to build proper character !
As long as we're going there for character building, could I suggest a left of passage instead? Take one road less traveled by, and all that. (It's "rite" of passage.)
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Old 04-15-22, 04:46 PM
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I never thought of cantilevers as being all that fuss. Now I"ve only owned the old Mafacs and an early Shimano that is a near exact copy of the Mafac for the geometry. (Levers stick straight out and snag cyclocross riders' legs on mounts and dismounts.) I think little of either pushing the canti arms inboard to compensate for pad wear or simply tightening the cable and angling the blocks up, back to the rim center. (And yes, you do not want to let those pads get too low.)

Oh. John, it seems you have cantis with the pad detail modeled after regular road brakes. A threaded rod that you run through the caliper arm and secure with a nut. Most cantis and all the old ones are a different system. There is a bolt through the caliper arm that runs fore and aft parallel to the rim. The head of the bolt has a hole the brake post (with no threads) goes through. The nut on the other side of the caliper pulls the bolt head and post snug up against the caliper arm. Very flexible for rotating the pad up and down and sliding in and out Toe-in took creativity on the old ones. I went to KoolStop pads decades ago and have had few squeal issues so I haven't sweated it.

John, you might consider tightening the cable at the clamp as a good preventive measure. Yes, it tires out cables. So you have to replace them far sooner. But ... those broken strands rarely cause a cable failure when riding unless you waited far too long AND they are very easy to see. If you do all you can to preserve that end it may just happen that the cable has worn through part of the ferrule at the brake hood and is now in metal to metal contact not as intended at the brake lever or somewhere else internal and you will never know until it breaks. When that happens, you'll have just enough time to utter "Oh s***" very loud. By regularly killing your cables at the brake clamp, you get to pull them out to see if any other issues are starting. Cables are consumables and if you don't treat them as such, they will bite you.

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Old 04-15-22, 05:18 PM
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Originally Posted by LV2TNDM View Post
Because as cantilever brake pads wear, they hit lower and lower on the rim until "OH CRAP!" they dive under the rim and NO MORE BRAKE!!! (Ask me how I know!)

Canti pads need to be set properly to hit the rim at the correct angle, achieve good leverage, avoid brake pad dive, prevent squeal, and make sure you aren't gonna slash that sidewall. Straddle cable length should be optimized for optimal leverage and braking power. Too long, not enough power, too short, too squishy.

Now if the OP actually means v-brakes, then (in an Emily Litella voice), "Never mind!" Set up still requires much of the above, but without the dire consequences. Many v-brakes require you just push the pad against the rim loose, make sure it's tangent and at the proper height, and tighten down the nut. Squeal was supposedly eliminated and toe wasn't necessary. (But we all know that isn't true, don't we!)
Adjusting the pad angle is one thing, but OP was talking about swapping concave spacers to adjust distance from the rim.
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Old 04-15-22, 06:10 PM
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Start here, read the PDF Brakes- installation instructions. If there's enough pad left looks like you readjust the main cable, realign the pads.

https://www.tektro.com/products.php?p=48

Last edited by grizzly59; 04-15-22 at 06:15 PM.
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Old 04-15-22, 08:49 PM
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Originally Posted by John Hawkinson View Post
As long as we're going there for character building, could I suggest a left of passage instead? Take one road less traveled by, and all that. (It's "rite" of passage.)
Indeed. Mea culpa. That is much more appropriate, as I'm left-handed and left dominant. Except for throwing a frizbee and using scissors, for unknown reasons. Have I LEFT anything out?!!!
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Old 04-15-22, 11:00 PM
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(Sorry for the delay and the perhaps overly pithy replies above, I was trying to get up to ten posts to lose the restrictions, but then I ran into the 5 post/day limit. Doh! No more posts another 7 hours…)

Originally Posted by grizzly59 View Post
Start here, read the PDF Brakes- installation instructions. If there's enough pad left looks like you readjust the main cable.
Err, yes, I'd reviewed that before the initial post.
(I even linked to it in a post above that appears to be stuck in moderation—responding to LV2TNDM's q about V or cantilever — oops. Maybe it'll show up soon.)
It doesn't really say anything about how pads should be spaced away from the brake arm -- the 1mm dimension given is a vertical one, the top of the pad should contact the rim 1mm down from the top of the rim — no manufacturer’s guidance on the rim/pad spacing during motion. (I suppose this depends on the lateral truing runout, but still).

Even so, like basically all the literature, it doesn't give any guidance on what to do if, months after the initial setup, a partially worn brake pad no longer provides sufficient friction when the barrel adjuster is maximized.
As noted in this thread, the two choices seem to be moving around the spacers and adjusting the brake cable.
Actually, I thought it was interesting that the Tektro instructions don't seem to say anything about setting the brake cable tension. Just the torque for the anchor bolt (6-8 Nm).

Originally Posted by hokiefyd View Post
For example, low profile cantilevers, like the Oryx brakes, usually respond well to a wider brake arm splay at rest. In other words, install the pads with the thickest spacers to the inside of the brake arm (which moves the pad closer to the rim, right?). This forces you to set the arms wider apart, which minimizes the loss of mechanical advantage that low profile cantilevers experience as they're actuated (pulled together). Your straddle cable will also generally sit lower with a straighter path between each arm (assuming you have the tire or fender clearance), which increases mechanical advantage.
Hrmm, I am confused by this — what is the adjustment that controls the width of the arms apart ("arm spacing")? As far as I'm aware, the Oryx adjustments are:
• Spring-pin pivot boss hole. Instructions say to use the middle, but nothing stops you from the others.
• Brake pad positioning via the threaded stud from the pad that has…well quite a few degrees of freedom: up/down; a little bit of side-to-side (slot is wider than the stud); rotation around the stud; and then—gosh, what's the nomenclature?—the ability to wobble off-axis from plane of the brake arm by a few degrees because of the conical spacers, which lets you set toe-in and match the angled plane of the rim.
• Brake cable tension
• Spring tension adjustment (2mm Allen key)

None of these seem to be about arm spacing?

Also, I vaguely recall reading some people suggest about not using the supplied "link wire" and instead fashioning some kind of alternative? Is that what is meant here? I don't know anything about that…

The relatively small amount of pad wear over the life of the pads (in terms of dimensions you can measure) can well be taken up by the barrel adjuster up at the brake lever.
Well would that it were so, but it seems not to be.
But maybe I'm not understanding. What does "in terms of dimensions you can measure" mean here?

Also: If cable tension really is the recommended solution here, why is the answer not to install additional barrel adjusters?
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Old 04-16-22, 04:38 AM
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Originally Posted by John Hawkinson View Post
what is the adjustment that controls the width of the arms apart ("arm spacing")?
It's the combination of the thick and thin spacer washers, as you're experimenting with here. With smooth post brake pads (as used with traditional cantilevers), you can freely slide the brake pads "in and out" of the cantilever mounting base -- to position the pads closer to or further from the brake arm. The different washer thickness with threaded post pads, as you have with the Oryx and as comes with nearly all linear pull brakes today), accomplishes the same thing. It lets you set the pads close to the brake arm (by using the thin spacers next to the pad) or further from the arm (by using the thick spacers next to the pad).

The geometry of low-profile cantilever brakes like the Oryx means that the mechanical advantage of the brakes decreases pretty rapidly as they rotate in towards the rim. This is why spacing the pads further from the arm (by using the thick spacers) is usually advantageous -- it keeps the arms splayed wider which reduces the loss in mechanical advantage as they rotate towards the rim.

I'm sure it's been posted somewhere above, but Sheldon Brown has an excellent article on this: https://www.sheldonbrown.com/cantilever-geometry.html

Browse down to the section for special considerations for low-profile cantilevers.

Originally Posted by Sheldon Brown
Traditional good practice had been to slide the brake shoe holders all the way into the eyebolts, so that the back of the shoe butts up against the cantilever arm. This is not the case with the newer low-profile models.With low-profile cantilevers,, the shoe needs to be extended inward from the arm, increasing the effective cantilever angle . The unsupported length of shaft connecting the brake shoe to the arm may cause an increased tendency to squeal, but that is one of the inherent trade-offs of low-profile brakes.
Originally Posted by John Hawkinson View Post
But maybe I'm not understanding. What does "in terms of dimensions you can measure" mean here?
I was trying to say that the brake pad wear doesn't contribute a lot to the geometry we're discussing here...it contributes some, but not a lot. I was suggesting that the spacers you're working with are not designed to compensate for pad wear. For that, you'd just snug the barrel adjuster a little bit.
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Old 04-16-22, 07:44 AM
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Originally Posted by John Hawkinson View Post
Great question. Of course the real answer is I didn't think about that.

But my experience is I get many years and sets of pads out of a set of brake cables, and that loosening and tightening the pinch bolt more than a few times leads to a freyed cable,
On the other hand, it's probably easier than messing around with swapping washers and spacers, and infinitely variably adjustable.

But it still leaves the real question: Is it normal to have to make this kind of adjustment over the life of a pad?
Cables do not last forever, are inexpensive to change, and make an often remarkable improvement when replaced. I replace the outers at the same time.
Also, make certain that your barrel adjusters are nearly all the way retracted and the shoes firmly against the rim when you set up the cable clamp so that you do not waste adjuster travel setting up the initial pad adjustment.
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Old 04-17-22, 05:03 PM
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Originally Posted by dsbrantjr View Post
Cables do not last forever, are inexpensive to change, and make an often remarkable improvement when replaced. I replace the outers at the same time.
Also, make certain that your barrel adjusters are nearly all the way retracted and the shoes firmly against the rim when you set up the cable clamp so that you do not waste adjuster travel setting up the initial pad adjustment.
It's actually the "outers," or cable housing that makes ALL the difference in brake performance and achieve remarkable improvement. New cables do very little to improve the situation. The orginal cables are covered by the housing, so the inside of the cable tends to stay relatively rust-free and clean, despite the exposed portions of the cable looking terrible. But the inside plastic nylon is what fouls over time, imparting friction to the cable. Dirt, grime, contaminants, corrosion, you name it, slowly impregnate the lining. You can't fix it. Flushing with solvent and relubricating won't do much. But fresh cable housing is eye-opening! Makes a bike's shifting and braking perform like it did off the showroom floor. And cable friction is like bad wheel alignment in your car - it sneaks up on you and gets bad slowly over time and you don't notice how bad it has gotten. Fresh cables and housing can be like an epiphany!

So if it came down to it and I could only replace ONE of the two, it would be cable housing every time. But when you're going to the trouble of this work, you always replace them in tandem.

And while you're doing this work, it's important to trim housing ends flat and perpendicular. Do not rely only on the ferrule to provide a "flat" surface for the housing to fit in the cable stop. I use a grinder to get the metal ends nice and flat. (A Dremel works too, as does a file, but not as quick and easy as a bench grinder.) Brake housing wire (wound circularly) always seems to "wrap around" on itself when cutting it to length. And even if you do manage to get a clean cut, you still have a non-flat end. Grinding gets it nice and flat and perpendicular. You just have to be careful not to overheat too much and melt the plastic liner and cover. Same with shift housing, despite the wires being aligned differently. Shifting is very sensitive to issues with the housing having friction or fouled ends. (And the wires to foul over time and they tend to start to protrude from the end.)

I have a good shift housing story. A customer who bought his bike from our LBS came in for some service; I think it was a flat tire. Either way, it was not shifting related. I completed the repair and gave the bike a quick check-over and lubricated the chain. I quickly noticed that the shifting was TERRIBLE. He saw my reaction and said, "Oh don't even TRY! I've had you guys work on the shifting ever since I bought it and it has never worked well." I was aghast and embarrassed that his bike never performed as expected or intended. So I checked it over, pulled the housing and cables out of the slotted guides. Sure enough, not only were the cables dry as a bone inside the housing, there was white powder on the cables. So I quickly lubricated the housing and reinstalled everything. Functioned like a charm. After I gave it a test ride, I let the customer take it out to see what he thought. "WOW! It has NEVER worked this well!" he exclaimed. I was so happy to have solved his problem and make his bike perform as it should have all along.

So, smooth, low-friction housing is important, and crucial for indexed shifting.
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