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Disc Brake Issue

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Disc Brake Issue

Old 05-28-21, 10:49 AM
  #1  
LS05
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Disc Brake Issue

I have a a Trek Checkpoint ALR5. It is equipped w/hydraulic disc brakes, Shimano 105 to be exact.
My problem occurs when riding, I spot an unavoidable bump or pothole and I apply the brakes, There is a rather violent vibration in the front brake after hitting the bump/pothole. It's as if the front brake is braking and immediately fading. The vibration continues until i release the front brake. When I engage the front brake again, on smooth road, front braking is normal. I do not have the same problem w/the rear brake.
I am a large rider. I'm 6'4", weighing 200 lbs. I've read that cycling disc brakes are susceptible to fade for large riders, but haven't come across anything like what I'm experiencing. My LBS has checked the front end integrity of the bike with no negative results.
Any thoughts would be appreciated.
Thank you
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Old 05-28-21, 11:12 AM
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The go-to answer for brake hysteresis issues is a glazed or inconsistant spot on the rotor. You may try to scrub the rotor with aluminum oxide sandpaper. A few hundred grit ought to be enough to knock off the contaminants that have glued themselves on.

Another answer is the rotor itself may have worn inconsistantly due to the various cut-outs providing differing surface contact areas. The least surface area parts (either side of the hole in the braking surface) would have worn more than the areas that contact the whole pad. In this case a new rotor (& maybe even pads) would be well worth looking in to.

A good measurement of rotor thickness would tell you a lot.

As a heavier & "confident" rider (200lb) that tends to push things, I'd like to suggest scintered/metallic brake pads. They may be a bit noisier in certain circumstances, but they do tolerate higher heat loads much better than the organic resin type. They also tend to be more fade resistant & tend to not deposit themselves on to the rotor so much.
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Old 05-28-21, 11:26 AM
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Also check headset adjustment.
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Old 05-28-21, 12:27 PM
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Thank you both...Will ask my wrench to address your suggestions.
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Old 05-28-21, 06:52 PM
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Originally Posted by base2
The go-to answer for brake hysteresis issues is a glazed or inconsistant spot
Agree. How is this hysteresis, though?
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Old 05-28-21, 07:18 PM
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Originally Posted by LS05
I have a a Trek Checkpoint ALR5. It is equipped w/hydraulic disc brakes, Shimano 105 to be exact.
My problem occurs when riding, I spot an unavoidable bump or pothole and I apply the brakes, There is a rather violent vibration in the front brake after hitting the bump/pothole. It's as if the front brake is braking and immediately fading. The vibration continues until i release the front brake. When I engage the front brake again, on smooth road, front braking is normal. I do not have the same problem w/the rear brake.
I am a large rider. I'm 6'4", weighing 200 lbs. I've read that cycling disc brakes are susceptible to fade for large riders, but haven't come across anything like what I'm experiencing. My LBS has checked the front end integrity of the bike with no negative results.
Any thoughts would be appreciated.
Thank you
I hope you're not actually holding the brake yet when the wheel makes hard contact with the bottom of the pot hole or opposite lip of the pot hole. You should be braking hard upon reflex when you first see the obstacle or pot hole and then in the split second before solid contact with the obstacle release the brake so the tire can roll over or through said obstacle. The way everything goes back to normal after your incident makes me think its got to do with the headset, but that's just my opinion.
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Old 05-28-21, 08:27 PM
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Originally Posted by MoAlpha
Agree. How is this hysteresis, though?
https://en.m.wikipedia.org/wiki/Hysteresis
Specificly, it is elastic hysteresis. It's under the "In mechanics" heading. The gist of it is the current state has a direct relationship to the previous state & a feedback loop of some sort is formed. Most people tend to associate it with magnetism or electronics, but the principal is found in many systems. This one example being the friction/force acting on the rotor at a given moment vs the elasticity of the fork. The area in between the curves being the sum of the change of velocity of bike, the bike rider, & some nominal heat gain in the rotor, pads, & elsewhere in the system.

Last edited by base2; 05-28-21 at 08:45 PM.
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Old 05-29-21, 05:10 AM
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Originally Posted by base2
https://en.m.wikipedia.org/wiki/Hysteresis
Specificly, it is elastic hysteresis. It's under the "In mechanics" heading. The gist of it is the current state has a direct relationship to the previous state & a feedback loop of some sort is formed. Most people tend to associate it with magnetism or electronics, but the principal is found in many systems. This one example being the friction/force acting on the rotor at a given moment vs the elasticity of the fork. The area in between the curves being the sum of the change of velocity of bike, the bike rider, & some nominal heat gain in the rotor, pads, & elsewhere in the system.
Thanks. I deal with hysteresis in neurophysiological systems from time to time, but never thought of it as an amplifier of fork vibration.
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Old 05-29-21, 06:52 AM
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Originally Posted by MoAlpha
Thanks. I deal with hysteresis in neurophysiological systems from time to time, but never thought of it as an amplifier of fork vibration.
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Old 05-29-21, 03:48 PM
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Originally Posted by LS05
I have a a Trek Checkpoint ALR5. It is equipped w/hydraulic disc brakes, Shimano 105 to be exact.
My problem occurs when riding, I spot an unavoidable bump or pothole and I apply the brakes, There is a rather violent vibration in the front brake after hitting the bump/pothole. It's as if the front brake is braking and immediately fading. The vibration continues until i release the front brake. When I engage the front brake again, on smooth road, front braking is normal. I do not have the same problem w/the rear brake.
I am a large rider. I'm 6'4", weighing 200 lbs. I've read that cycling disc brakes are susceptible to fade for large riders, but haven't come across anything like what I'm experiencing. My LBS has checked the front end integrity of the bike with no negative results.
Any thoughts would be appreciated.
Thank you
I'm not sure why you think this vibration is related to brake fade? Brake fade is a loss of braking power due to the build up of excessive heat. Braking for a pot-hole is not going to cause brake fade!

It would also help to know what is actually vibrating? Is it the brake rotor itself or the bike forks? Obviously if something is slightly loose (caliper, rotor, headset, wheel hub etc) that could cause vibration under braking. But you can also get vibration from one of the components resonating. For example I had an old mtb that used to suffer from a really bad rear frame vibration under heavy braking. It was simply down to the resonant frequency of the chainstays, along with worn suspension pivot bearings. Fitted new pivot bearings and the vibration magically disappeared.

The fact that you don't have this problem on smooth roads does point toward something being loose or worn with play. Loose/worn headset would be my first guess. Play in your front wheel hub second. Probably also worth tossing in a new set of front brake pads to see if that makes any difference. Make sure the rotor is clean, running true and not glazed too.
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Old 05-31-21, 06:42 PM
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Seems to me it’s likely fork flex. Bigger rider, hard braking, flex in the fork will result in some flex that will be sort of a stuttering that’s consistent with what the OP describes.

Take away, try to brake more smoothly,and if you get some stuttering with hard braking don’t worry about it.
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Old 05-31-21, 07:53 PM
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Originally Posted by base2
I hope you don't mind if I borrow your slogan (My lights are obscenely bright because drivers are dim.) I seem to find myself in need of it. I'll return it when I'm done with it, thanks,
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Old 06-02-21, 07:53 AM
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Originally Posted by Bigbus
I hope you don't mind if I borrow your slogan (My lights are obscenely bright because drivers are dim.) I seem to find myself in need of it. I'll return it when I'm done with it, thanks,
Anytime. If I need it back I'll know where to go.
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Old 02-10-23, 07:41 AM
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I have exactly the same problem

Originally Posted by LS05
I have a a Trek Checkpoint ALR5. It is equipped w/hydraulic disc brakes, Shimano 105 to be exact.
My problem occurs when riding, I spot an unavoidable bump or pothole and I apply the brakes, There is a rather violent vibration in the front brake after hitting the bump/pothole. It's as if the front brake is braking and immediately fading. The vibration continues until i release the front brake. When I engage the front brake again, on smooth road, front braking is normal. I do not have the same problem w/the rear brake.
I am a large rider. I'm 6'4", weighing 200 lbs. I've read that cycling disc brakes are susceptible to fade for large riders, but haven't come across anything like what I'm experiencing. My LBS has checked the front end integrity of the bike with no negative results.
Any thoughts would be appreciated.
Thank you
I've been dealing with a similar problem with my trek checkpoint alr5 for almost a year now. Your description is almost exact to my experience. Going down a hill if I brake and hit a bump in the road while braking, the front wheel goes into considerable vibration and braking power severely impaired until I release the brake and reapply the brake. On smooth roads I never have a problem.

I have changed the disc brakes and pads. This did not fix the problem. I thought maybe there was a problem with the forks. I replaced the forks and again this did not solve the problem. I'm wondering if this is a design problem.

Did you manage to get to the bottom of your problem?
By the way, I am quite a light weight person (70kg). I don't think being heavier is the issue either.

Last edited by Maquilina; 02-10-23 at 07:44 AM.
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Old 02-10-23, 08:12 AM
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If you - completely or lightly - release the brake lever before hitting the pothole, what happens? Dumb question, but...

It's clearly no good to brake while hitting a pothole for various reasons. There's already a good amount of force (vertical) being put on the headset when that happens. When you're also braking, there's an additional force (horizontal, for lack of a better word) acting.

Seems like we need a physicist!
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Old 02-10-23, 12:32 PM
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Originally Posted by Maquilina
I've been dealing with a similar problem with my trek checkpoint alr5 for almost a year now. Your description is almost exact to my experience. Going down a hill if I brake and hit a bump in the road while braking, the front wheel goes into considerable vibration and braking power severely impaired until I release the brake and reapply the brake. On smooth roads I never have a problem.

I have changed the disc brakes and pads. This did not fix the problem. I thought maybe there was a problem with the forks. I replaced the forks and again this did not solve the problem. I'm wondering if this is a design problem.

Did you manage to get to the bottom of your problem?
By the way, I am quite a light weight person (70kg). I don't think being heavier is the issue either.
That does sound like a resonance issue. Hitting a bump under braking is probably the trigger for the resonance, which will then tend to amplify until you release the brake and re-apply.

The hard part is finding out what component is actually resonating. It sounds like you’ve changed most of the obvious parts, but what about the front wheel?

You could also try taping a few small lead weights to suspect components like the forks and see if the vibration goes away because of a change in the resonant frequency. Tyre pressure might also have an effect.

As I mentioned much earlier in this thread, I had a mountain bike that was prone to rear brake resonance through the rear chain stays when the pivot bearings were worn. Bumpy descents would trigger the resonance much more than braking on smooth surfaces, which made it a pain to diagnose.
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Old 02-10-23, 03:29 PM
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Originally Posted by eduskator
If you - completely or lightly - release the brake lever before hitting the pothole, what happens? Dumb question, but...

It's clearly no good to brake while hitting a pothole for various reasons. There's already a good amount of force (vertical) being put on the headset when that happens. When you're also braking, there's an additional force (horizontal, for lack of a better word) acting.

Seems like we need a physicist!
It's not necessarily a pot hole that triggers the vibration. It could be a bump in the road that I can't see. It also doesn't happen every time. In any case I have avoided the vibration by doing what you suggest if I know I'm coming to a bumpy surface which has triggered the vibration before. However, sometimes I don't always have the luxury of doing so if I'm on a new road and don't see the little bumps. My other bikes have never displayed this behavior. I think you're right. There is some "physics" perculiar to this particular bike.

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Old 02-10-23, 03:42 PM
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Originally Posted by PeteHski
That does sound like a resonance issue. Hitting a bump under braking is probably the trigger for the resonance, which will then tend to amplify until you release the brake and re-apply.

The hard part is finding out what component is actually resonating. It sounds like you’ve changed most of the obvious parts, but what about the front wheel?

You could also try taping a few small lead weights to suspect components like the forks and see if the vibration goes away because of a change in the resonant frequency. Tyre pressure might also have an effect.

As I mentioned much earlier in this thread, I had a mountain bike that was prone to rear brake resonance through the rear chain stays when the pivot bearings were worn. Bumpy descents would trigger the resonance much more than braking on smooth surfaces, which made it a pain to diagnose.
Yes I agree with your conclusion. I may need to try to change the wheel. Are there any other components that could also be considered. As I said, I've changed the brakes, the forks, and as you've suggested I could change the wheel. After that I can't think of anything else.
Your idea about attaching weights is a good one - thanks.
If the wheel doesn't fix the problem then I may have to part company with this bike. I don't think anyone would be rushing to buy it off me though . I couldn't in good conscience sell it without disclosing my problem.
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Old 02-10-23, 05:44 PM
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I recently had just such a resonance issue that appeared when I put an older tire back on my front wheel and disappeared the next day after I put on a different tire. Little things can change a resonant frequency.
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Old 02-10-23, 05:50 PM
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Originally Posted by DangerousDanR
I recently had just such a resonance issue that appeared when I put an older tire back on my front wheel and disappeared the next day after I put on a different tire. Little things can change a resonant frequency.
Very interesting. When I bought the bike I actually requested different tires. Most of my riding is in the road so I chose a narrower road tire. You may have nailed the root cause. Thanks I will try to revert to the original tires!
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Old 02-10-23, 08:19 PM
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Maquilina:
Please do be careful. My old Peugeot would do this to me almost exactly at 30 MPH if I was pedaling hard to hold the speed, so I got very used to dealing with a resonant wobble. On the Peugeot I could stop the wobble by pressing one leg against the top tube. There may not be anything "wrong" with anything. It may just be that things add up to being unstable when you bump them like that.

The recent incident was on my Lynskey R350 which is not a flexible flyer by any stretch of the imagination. The front wheel is from Light Bicycle and is a 46 mm rim brake wheel built on a Carbon Ti hub. Nothing dodgy in the front end. Cane Creek Headset in good condition. Oh, I was about 245 pounds when this happened.

This wobble started at about 25 MPH. It showed up in a group ride. I am afraid that I scared the <expletive> out of the guys who were riding right behind me. The leg on the top tube worked to damp the wobble; I do that reflexively thanks to my trusty old Reynolds 531 steel frame wet noodle of a Peugeot.
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Old 02-11-23, 04:16 AM
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Originally Posted by Maquilina
Yes I agree with your conclusion. I may need to try to change the wheel. Are there any other components that could also be considered. As I said, I've changed the brakes, the forks, and as you've suggested I could change the wheel. After that I can't think of anything else.
Your idea about attaching weights is a good one - thanks.
If the wheel doesn't fix the problem then I may have to part company with this bike. I don't think anyone would be rushing to buy it off me though . I couldn't in good conscience sell it without disclosing my problem.
As Dan mentioned, a different tyre would be an easy test. I would also double check headset bearings and caliper mounts to make sure nothing is loose or has any play.
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Old 02-11-23, 04:19 AM
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Originally Posted by DangerousDanR
Maquilina:
Please do be careful. My old Peugeot would do this to me almost exactly at 30 MPH if I was pedaling hard to hold the speed, so I got very used to dealing with a resonant wobble. On the Peugeot I could stop the wobble by pressing one leg against the top tube. There may not be anything "wrong" with anything. It may just be that things add up to being unstable when you bump them like that.

The recent incident was on my Lynskey R350 which is not a flexible flyer by any stretch of the imagination. The front wheel is from Light Bicycle and is a 46 mm rim brake wheel built on a Carbon Ti hub. Nothing dodgy in the front end. Cane Creek Headset in good condition. Oh, I was about 245 pounds when this happened.

This wobble started at about 25 MPH. It showed up in a group ride. I am afraid that I scared the <expletive> out of the guys who were riding right behind me. The leg on the top tube worked to damp the wobble; I do that reflexively thanks to my trusty old Reynolds 531 steel frame wet noodle of a Peugeot.
Sounds scary!
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Old 02-13-23, 05:49 PM
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Back when I ran my first company (locksmithing) we used to train people to look for the obvious stuff first because it inevitably was the solution (eg trying to see if another door was unlocked in locksmithing).

My first thought when reading this was you're loose on the wheel somewhere. Bearings have play, thruaxle or qr aren't tight, rotor isn't tight, caliper isn't tight, headset, etc. Please take the time to eliminate those as causes. It will save you a lot of this stuff ^ and I would lay odds that's actually your problem.
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Old 02-13-23, 07:10 PM
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I'm no expert but there are a ton of possibilities:
1. Wheel. Remember the brakes act on the hub with disc brakes. Spokes might deflect with the extreme force. I've seen a few e-bikes that actually had major spoke issues with heavier riders.
2. I have noticed that center lock rotors tend to get a little play in the splines if not tightened correctly
3. The forks- the rotor is anchored to one side or the other. When braking, the caliper is twisting that leg commensurate with braking force
4. Frame geometry. Basically the rake could cause a different feel.
5. could the brakes possibly need bled. They might act different under the extreme circumstances. Also-could the hydraulic hose cause an issue.
6. Headset, as mentioned above, could cause this as well

As I stated-I'm no expert, just trying to envision possible causes. With rim-brakes, half the possibilities would be removed. I have both types on my bikes-each one has something to offer.

Good Luck
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