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PostPosted: Mon Aug 14, 2017 4:19 pm 
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Joined: Sat May 24, 2014 12:09 pm
Posts: 758
Hi, today, I experienced severe fork chatter twice. Both times, it happend when braking only with the front, at moderate speed, but on really brooken tarmac. Is this common with all disc road bikes? 2 additional things:

* I have light vibrations on the front brake alost all the time, especially when braking hard
* I have the feeling the fork of the Endurace is not the stiffest of the bunch regarding braking forces. Rocking the bike front to back with the front brake locked causes a lot of flex in the fork. Same question here : is this a general behaviour with road disc bikes?

I like the disc "thing" a lot, (the bike has already >8000 km's since purchase in november last year, and the Addict get used a lot also) but today's experience learned me that fork stiffness front to back, is an important criteria for the next disc bike!!

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Canyon Ultimate CF SLX 2013
Scott Addict Orica Greenedge
Canyon Endurace CF SLX


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PostPosted: Mon Aug 14, 2017 4:31 pm 
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This sounds more like pad flutter than the fork. Pretty much all disc bikes you will feel the pads moving if you hold the front brake and shift the bike forward and backward.


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Posted: Mon Aug 14, 2017 4:31 pm 


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PostPosted: Mon Aug 14, 2017 5:16 pm 
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Joined: Sun Jan 08, 2017 12:44 pm
Posts: 60
Are you sure you have stem bolts properly tightened on prescribed torque? I had similar problems and torque wrench made the difference since I always tightened the bolts on lower torque by hand than it should have been.


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PostPosted: Mon Aug 14, 2017 6:40 pm 
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How big are the rotors? In any case, maybe clean the pads/rotors with alcohol, dry, and place in oven for a bit.

Does it happen only in high-grip (uphill braking)?

Is your QR tight and of good quality? Do the wheels have adapters that fit right?

Is there verticle play in the headset? Is the headset tq'd down vertically correctly (stem center cap bolt first, then others?)

Are the headset spacers right for the bike and all the same?


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PostPosted: Mon Aug 14, 2017 7:03 pm 
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I had a mountain bike with a shudder in the rear. I fixed it by sanding the rotors with emery cloth and installing new pads.

It's probably just like car rotors where you can get burnt pad deposits on the rotors. When the pad hits that section it grabs harder and makes the shudder.

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PostPosted: Mon Aug 14, 2017 7:24 pm 
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Joined: Sat May 24, 2014 12:09 pm
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There is 0 play on any of the components and all the bolts are torqued to spec. The Endurace uses TA's, and those are also torqued to >10 nm. Rotors are 160mm. While shuddering, I coud see the fork go back and forth, the same as while rocking the bike front to back. To me, it's clearly a fork issue. While riding, the confort up front is really good, so there must be some 'give' in the fork, maybe a little too much to cope with the heavy disc brake forces applied to a fork?? I just cleaned the rotors and pads with brake cleaner. Vibrations are a lot less, and i could not make the shudder happen, even if trying to brake hard on bad pavement. But I never had it to happend in 8000 km's neither... But the fact remains : there is (to much for my liking) movement in the fork while braking.

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Canyon Ultimate CF SLX 2013
Scott Addict Orica Greenedge
Canyon Endurace CF SLX


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PostPosted: Tue Aug 15, 2017 2:31 am 
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Joined: Mon Aug 29, 2016 11:19 am
Posts: 378
I don't have disc brakes but here is my theory...

Only one fork leg should be flexing and as a result the bike should feel like changing direction ever so slightly.

Have you tried comparing a somewhat looser skewer to a tighter one if you get any difference?

Is there any difference when going down a 10 degree slope braking hard at lower speeds and with braking hard on flat or gentle descents at high speeds?

How about trying different brake pads, these are perhaps too grippy under hot temperature conditions.

/a


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PostPosted: Tue Aug 15, 2017 3:36 am 
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Posts: 241
I got brake chatter until the LBS re-installed the fork, preloaded the headset properly and tightened the stem bolts up to spec. No harm for you to check them out.


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PostPosted: Tue Aug 15, 2017 4:22 am 
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Posts: 346
+1 for the issue at the disc/pad interface.

The reason for this (although you don't mention it) is that the presumption is that it has started, but wasn't always there.

Based in similar experience some time ago on my disc roadie.


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PostPosted: Tue Aug 15, 2017 12:28 pm 
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Joined: Fri Feb 18, 2005 6:50 pm
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Location: Wilmington, DE
The only time I experienced fork chatter during braking I didn't have the headset bearings tight enough. They felt plenty tight in the stand and I couldn't detect any play when holding the brake and rocking the bike but hard braking with the front disc made the minuscule play very apparent. Preload your headset bearings until they get tight then back off just enough to loosen them up. That ought to fix it. I used to set headset preload by only going tight enough to remove any apparent play but that only works with loose ball headsets, not cartridge bearing like everything modern.


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PostPosted: Tue Aug 15, 2017 1:00 pm 
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joejack951 wrote:
The only time I experienced fork chatter during braking I didn't have the headset bearings tight enough. They felt plenty tight in the stand and I couldn't detect any play when holding the brake and rocking the bike but hard braking with the front disc made the minuscule play very apparent. Preload your headset bearings until they get tight then back off just enough to loosen them up. That ought to fix it. I used to set headset preload by only going tight enough to remove any apparent play but that only works with loose ball headsets, not cartridge bearing like everything modern.


Will give it a try. Headset is tight, but i can imagine braking forces tend to highlight the tinniest amount of play in the headset

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Canyon Ultimate CF SLX 2013
Scott Addict Orica Greenedge
Canyon Endurace CF SLX


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PostPosted: Tue Aug 15, 2017 3:19 pm 
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Joined: Tue Jul 26, 2016 5:21 pm
Posts: 120
I had the same experience when I tried changing spacers from one diameter to another. Is your fork compatible with that topcap?


I'll get chatter on dirt when there is more grip. Have you lowered the tire pressure recently?

You can try loosening the front wheel TA and checking the disc bolt(s).


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PostPosted: Sun Oct 01, 2017 7:49 am 
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I had this problem, and after eliminating all components of the braking system, I discovered the non disc side spoke tensions on my front wheel were very inconsistent. Tightened them up so they all twanged to the same note : problem solved!


Sent from my iPad using Tapatalk


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PostPosted: Mon Oct 02, 2017 6:36 pm 
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Posts: 403
If possible, repeat the test with a different pad and rotor. The fork is no doubt flexing, but it should flex back smoothly when brakes are applied evenly and then return smoothly when the brakes are released. If it is juddering back and forth, that suggests that the brake force is varying in an irregular fashon, which could be contamination of the pads and rotors, glazing, etc...

What kind of rotor is it? The hole patterns in some rotors are also prone to chattering or pulsation, even without contamination.

P.S. The fork certainly has some flex. It is unavoidable, and is even designed in, as most forks, particularly on endurance bikes, have for/aft "splay" designed in to smooth the ride over bumps. There has been some criticism of disc versions of popular bikes, with reviewers saying they feel harsher than the rim brake version of the same bike, which is usually attributed to the increased reinforcement needed to deal with the loads of the disc brake. Designers are trying to strike a very fine balance between stiff enough for stable disc braking, and flexy enough for a ride that isn't noticeably harsher than a rim version.


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Posted: Mon Oct 02, 2017 6:36 pm 


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PostPosted: Mon Oct 02, 2017 9:49 pm 
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Joined: Sat May 24, 2014 12:09 pm
Posts: 758
TheKaiser wrote:
If possible, repeat the test with a different pad and rotor. The fork is no doubt flexing, but it should flex back smoothly when brakes are applied evenly and then return smoothly when the brakes are released. If it is juddering back and forth, that suggests that the brake force is varying in an irregular fashon, which could be contamination of the pads and rotors, glazing, etc...

What kind of rotor is it? The hole patterns in some rotors are also prone to chattering or pulsation, even without contamination.

P.S. The fork certainly has some flex. It is unavoidable, and is even designed in, as most forks, particularly on endurance bikes, have for/aft "splay" designed in to smooth the ride over bumps. There has been some criticism of disc versions of popular bikes, with reviewers saying they feel harsher than the rim brake version of the same bike, which is usually attributed to the increased reinforcement needed to deal with the loads of the disc brake. Designers are trying to strike a very fine balance between stiff enough for stable disc braking, and flexy enough for a ride that isn't noticeably harsher than a rim version.


Rotors and pads are the stock Shimano items that came with the 785, so nothing special or exotic. I have not ridden the Endurace a lot since mid august, and the few time I went out with it, no chatter, but I didn't have any in 8000 km's before it happend twice. The new disc bike will be there 3th week of oct, I'm curius to compare fork stiffness between the Endurace and Addict disc.

_________________
Canyon Ultimate CF SLX 2013
Scott Addict Orica Greenedge
Canyon Endurace CF SLX


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