Cantilever brakes
 

I'm pretty much strictly a road cyclist, and I do all my own maintenance on my bikes. A couple years ago I got a neighborhood friend of my now 21 y.o. son into cycling as one of his off-season conditioning activities (he's on the Yale rowing crew). At first he was using one of my bikes. Then, he obtained a good bike through a family friend. The bike is kind of a cyclocross-road bike hybrid with road wheels/tires. But he's only road riding. I guess it's a cyclocross frame, and it has canti brakes. This week, he asked me to tune it up for him so that it'd be in good condition to take back to school. Honestly, I had never ridden a 'cross bike...nor even one with the cantilever brakes. There weren't any big issues with it. Just need wheels trued, brakes adjusted, shifting checked. And, he said the front brakes were "shuddering." When I rode it...WHOA!!! That scared me when I applied the front brakes. At first I thought it was simple a "toe-in" issue of the pads. But then I got on-line and read that it's pretty much an inherent issue with them. But...that it can be dangerous...especially with carbon forks (which this bike has) because it can cause the fork to break. One suggestion I found to diminish it is to switch to smaller pads. Which I did. The problem isn't completely eliminated. But it's WAY less than it was, and at least the front brake is usable. But, thinking about the "inherent" issue with these canti brakes...doesn't that happen when you're on a 'cross trail? Does the moisture and mud keep them from shuddering like that? Just curious.



Dan

A lot of people switched to a crown mounted cable stop.

where is the cable stop on this bike? it might be mounted to the crown of the fork, on the headset, or even the stem. IME, the lower the cable stop is, the better. so a fork-mounted stop is the best option. if you don't already have one there, you can get one cheap. you'll need to replace the front brake cable housing because the existing one is probably not long enough.

got a photo of that bike?

If you don't have a convenient way to stick the stop on the fork crown, another way to move the stop to the brakes is by switching to a mini-v.

Check to see that the bolts attaching the brakes to the canti bosses are tight. It's an obvious thing, but sometimes it doesn't get tight enough.

https://cimg9.ibsrv.net/gimg/bikefor...1243a6ada6.jpg

This is what everyone is referring to. Use washers/spacers to set the cable stop far enough out to clear the headset. It helps reduce vibration and pulsating.

Also, loosen the stem then check to ensure the headset preload is properly set.

I just don’t see how the cable stop would eliminate the shudder.

Dan

The shudder is mostly due to flex in the steerer tube. Putting the stop on the crown makes the whole system a lot less compliant.

I'm surprised you didn't see this recommended a lot in your internet searches.

Actually I did see it. But since it wasn't my bike...the quickest, and easiest fix was to go to the smaller brake pads. But I think I'll recommend an addition/switch of the stop.

Dan

I'm not a fan of cantilever brakes, but my touring bike has them which allows the use of a fatter tire.

I had the same shuddering issue with the front brake when I replaced the original brake pads with more aggressive pads. I went back to less aggressive pads (which, unfortunately, require greater force) to resolve the issue.

The crown mounted stops are a lot more expensive than I thought they would be. I have one, but I didn't like how many spacers I was going to have to use to get it to work with the crown on the bike it was for. And the shuddering wasn't that bad on that bike either. Probably because the braking was weak due to the location of the brake bosses.

the FIRST thing to consider is brake pad toe-in. the pads might be less noisy if you angle the pad so the front hits the rim first, then flattens out. this is tricky to do with canti brakes

the last time I owned a bike with canti brakes, the brakes sucked and were noisy to boot. my experience that helped a lot was:
1. mount the cable stop at the fork crown instead of top of the head tube. that make the shuddering go away. $15 fix.
2. angle the pads with a toe-in bias. this made most of the squeal go away
3. replace the short "road" pads with some longer, curved "mtb" pads. these made the brakes work 100x better. I went from "slow down" at full effort to "lock up both wheels" with one finger gently pulling the lever. it that's too much brake for you, you can get more modulation with a more aggressive toe-in angle.

all that worked for me. YMMV.

I was able to eliminate front brake shudder on my old CX bike by adjusting the toe-in and contact angle of the cantilever brake pads.
If he's only riding road, switching the brakes out to mini-v's are a great option. They will give way more stopping power and have no shudder. I ran TRP CX 9.0's on my canti CX bike for years and they work great, but you have to run the pads super close to the rims.

This is absolutely, 100% nonsense. Cantilever brake shudder can’t and won’t cause a carbon fork to break. No doubt, extreme brake shudder is very scary, but this sounds like you’ve stumbled across some anti carbon fiber propaganda somewhere. If a fork crown cable stop doesn’t eliminate the problem, or if the fork isn’t drilled at the crown, another option is to replace the front brake with a mini-v brake. That will tend to pretty much solve it.

The bike in question in my OP isn't currently using a crown-mounted stop. But...I know it's drilled for one becasue I recall looking at the hole and thinking that I could mount a spare side-pull caliper on it (but obviously didn't cause it'd leave the canti lugs weirdly exposed). Although the smaller pads have mostly eliminated the shudder...I've told the kid that I want to properly correct it...told him to bring the bike next time he's home from school.

Still the cause/correction is baffling to me. I just don't see how moving the cable stop from the steerer to the fork crown eliminates the shudder.

Dan

I dont believe it eliminates the shuddering on all bikes. Some shudder more than others. Ive read that varbon forks shudder more than steel(who know if true). I've read tall head tubes are more prone to shudder due to distance between the headset stop and the brake hanger.

There is no 1 exact solution and sometimes its just 1 change or other times its multiple changes to fix the issue.

The way I understand it:
When you apply the brake, the fork and steerer below the head tube flex a bit. If the cable is hung from way up high on the stem/steerer above the head tube, which doesn't flex, the flexing of the fork and steerer below changes the distance between the hanger and brake (very slightly) which alters the tension on the cable and changes how aggressively the brake pads are grabbing the rim. This change in tension causes the brake to grab more aggressively then quickly release as the fork flexes back.

By lowering the cable down onto the crown, the mounting point is much closer to the brakes, so when the whole thing flexes, the distance between the hanger and brakes stays the same (or at least changes a lot less), so the pressure applied on the rim stays more consistent.

You can think of the system as a bow, with the cable between the anchoring points as the bowstring and the frame and fork elements across the same distance as the bow back. If you pull on a bowstring, the string itself isn’t elastic, so it puts a force on the bow back, bending it. If you apply the same force to a bowstring on a longer and a shorter bow, the longer bow is going to bend more than the shorter one. Thats why shudder is worse with a longer run of exposed cable between the cable stop and the brake. The pull on the string that causes the shudder is the brake pads grabbing on the rim and therefore tugging on that cable before releasing again. This cycle repeats several times per second and is the reason why things like toeing in the brake pads, changing brake pad materials or rims can reduce the strength of the shudder - by reducing the grabbiness of the brake pads, this cycle happens more rapidly and with less force.

grolby and msu...thanks. I get it now.

Dan

Neither did I until I installed one. But it really works.

OP, thanks for digging up that smaller pads do better. My Mooney has been getting worse over the decades. Pads and shoes keep getting bigger. So back to the short little pads we used 40 years ago and my shudder might go back into hiding? (I never saw it the first two decades.)

I'd get the fork hanger except I use longer saddles so to get the braking I like. I need to make my own fork hanger. Fully doable, just yet another project.

It happens because as you squeeze the brake, the braking forces bend the fork back and the brake bosses also down slightly, This lengthens the distance from hanger to brake. Longer distance means tighter cable and more braking. More fork bend. Eventually, fork springs back, shortening the distance and loosening the cable. One wobble cycle completed. Repeat until ... Mount the hanger on the fork and it moves down as the fork bends back (some of this bend is happening in the steerer above the headset). Little change in distance between hanger and brake.