Front Braking Problem

[Mtl_Biker]

I went for a long ride yesterday (terribly hot and humid) but at about three quarters of the route I noticed a problem when using the front (disc) brake... When I’d apply the brake while moving the front wheel would tilt towards the brake side (left) quite drastically. From the riding position I’d say it moved left by about an inch.

I got off the bike and started checking... the quick release axle was properly tight and I couldn’t see anything wrong. Without the bike moving I applied the brake and all appeared fine. I couldn’t see anything loose or wrong. The wheel was spinning perfectly true without the brake being applied. I started riding again but still the wheel would move left a LOT when I’d apply the brake. It scared me, especially since on some downhills I’d hit 52 kph! I was afraid that the wobble might cause a crash.

So I returned home at a much slower speed and without touching the front brake at all.

I don’t know how long this issue has existed... I don’t usually watch the wheel while braking. And my last few rides were just 20 km loops where I wouldn’t have to touch the brakes at all until back in my driveway. But now that I’ve seen it moving I’m real concerned.

Any ideas, anyone?

 

[Nova Haibike]

Are the steering bearings a.k.a the headset adjusted properly? The steering should be smooth with no binding but also without looseness. Checking and adjusting the headset:

 

[J.R.]

I'll never forget my first experience with disc brakes, my first were good hydraulic disc brakes. I hit the hill I live on and went bombing down 850 feet elv, 2.2 miles. Pedaling not needed I concentrated on the new bike and braking. The front wheel flexed left everytime I hit the brakes, I thought dramatically. Shocked me! Turns out that's very normal. Since then I've noticed every bike since has done the same. The larger the diameter and thinner the wheel, the more it flexed.

One inch seems extreme. I'd really check on that. Take a zip tie and install on the right side fork. Cut it so it just touches the rim or tire. Watch it when you brake. I bet it's not moving an inch. Looks more dramatic when looking at the tire without a reference.

Edit: Googling the issue turns up a lot of references if the flex while braking.

bicycle front wheel flexing when using disc brakes - Google Search

 

[Sierratim]

A quick way to check the headset adjustment is to firmly apply the front brake and push the bike forward and pull it back using the handle bars. If you notice any movement, the headset needs servicing.

With that said, 1" movement towards the rotor while braking is alot. You should get this resolved before riding again.

I'd also check the wheel hub adjustment by holding the bike upright and grabbing the top of the tire on the front wheel. Push back and forth firmly. If you feel any movement, adjust the front hub.

How old is you bike? Model?

 

[Mtl_Biker]

Are the steering bearings a.k.a the headset adjusted properly? The steering should be smooth with no binding but also without looseness. Checking and adjusting the headset:

The headset seems correct... but if it isn’t, could that really cause the wheel to tilt to the left when braking?

 

[Mtl_Biker]

A quick way to check the headset adjustment is to firmly apply the front brake and push the bike forward and pull it back using the handle bars. If you notice any movement, the headset needs servicing.

With that said, 1" movement towards the rotor while braking is alot. You should get this resolved before riding again.

I'd also check the wheel hub adjustment by holding the bike upright and grabbing the top of the tire on the front wheel. Push back and forth firmly. If you feel any movement, adjust the front hub.

How old is you bike? Model?

Please help me understand this... if the headset needs servicing (I really don’t believe it does) how could that cause the wheel to tilt to the left when braking?

The 1” movement is my perception of the amount of movement when I’m moving fast and apply the front brake. It’s my 3rd bike with disc brakes and I’ve never seen (or at least noticed) this kind of thing before.

It‘s a 2019 Giant Explore E+1 GTS, bought new in late fall last year and not ridden during our winter (snow) or during lockdown. The bike has about 1500 km on it now.

 

[Nova Haibike]

The headset seems correct... but if it isn’t, could that really cause the wheel to tilt to the left when braking?

I do not know, but I was attempting to eliminate a possible source of the problem. You have the caliper itself, the rotor, the front hub, the spokes, the front fork, and the headset. You checked to brake and rotor, and you said the wheel was straight. So I assume the brake is okay, and the wheel as well. Since the bike is new, I would not think the fork itself could be a problem; it is not like it would be old and possibly worn with play in the stanchions. So that left the headset.

Now, J.R. said he experienced it himself. His explanation seems plausible. Perhaps your wheel is visually straight but the spokes are under tensioned?

 

[Nova Haibike]

The 1” movement is my perception of the amount of movement when I’m moving fast and apply the front brake. It’s my 3rd bike with disc brakes and I’ve never seen (or at least noticed) this kind of thing before.

It could be you are experiencing a type of shimmy?

 

[Mtl_Biker]

I'll never forget my first experience with disc brakes, my first were good hydraulic disc brakes. I hit the hill I live on and went bombing down 850 feet elv, 2.2 miles. Pedaling not needed I concentrated on the new bike and braking. The front wheel flexed left everytime I hit the brakes, I thought dramatically. Shocked me! Turns out that's very normal. Since then I've noticed every bike since has done the same. The larger the diameter and thinner the wheel, the more it flexed.

One inch seems extreme. I'd really check on that. Take a zip tie and install on the right side fork. Cut it so it just touches the rim or tire. Watch it when you brake. I bet it's not moving an inch. Looks more dramatic when looking at the tire without a reference.

Edit: Googling the issue turns up a lot of references if the flex while braking.

bicycle front wheel flexing when using disc brakes - Google Search

I don’t need a zip tie to test... I already have a reference - my bike has fenders and when braking the wheel shifts to the left very dramatically. It really moves about an inch.

And it’s my third bike with disc brakes. I’ve never noticed such a thing before.

Back to work in the morning unfortunately, and I probably won’t be able to look at this again until Sunday. Gonna be a busy week for me with two key people on vacation.

 

[Mtl_Biker]

It could be you are experiencing a type of shimmy?

What do you mean?

 

[Mtl_Biker]

I do not know, but I was attempting to eliminate a possible source of the problem. You have the caliper itself, the rotor, the front hub, the spokes, the front fork, and the headset. You checked to brake and rotor, and you said the wheel was straight. So I assume the brake is okay, and the wheel as well. Since the bike is new, I would not think the fork itself could be a problem; it is not like it would be old and possibly worn with play in the stanchions. So that left the headset.

Now, J.R. said he experienced it himself. His explanation seems plausible. Perhaps your wheel is visually straight but the spokes are under tensioned?

I’m going to pull the wheel from the bike and check the hub adjustment. And try to check the spoke tension. (It‘s years since I built my own wheels but I still have a truing stand and a dish tool.)

 

[Nova Haibike]

A shimmy is an uncontrolled oscillation. It happens on some bicycles, often going downhill at speed, but it can happen on flat ground as well. I am merely thinking out loud that perhaps you are experiencing the onset of shimmy without it becoming an actually shimmy where the wheel moves both left and right. But generally shimmying does not occur during braking, at least not that I have ever heard of.

 

[J.R.]

I don’t need a zip tie to test... I already have a reference - my bike has fenders and when braking the wheel shifts to the left very dramatically. It really moves about an inch.

And it’s my third bike with disc brakes. I’ve never noticed such a thing before.

Back to work in the morning unfortunately, and I probably won’t be able to look at this again until Sunday. Gonna be a busy week for me with two key people on vacation.

Yes the fenders would help. My wheels do flex a little, but just a little. Nova might be on to something with spoke tension. I've even seen brand new bikes needing wheels tuned and trued. I true my wheels once a year. They generally aren't out by much.

 

[indianajo]

I would turn the bike upside down and check the wheel bearing. With the fork frozen by the ground, the wheel should be able to be tipped no more than 1/8" by pulling on the tire.
If more than that, it is possible the wheel nut is loose, or the cones holding the balls in the race are loose. Or perhaps some balls are missing.
I'd also check the spoke tension. On the 26" wheels I own, properly tightened spokes ping about F4 (piano note) when tapped with a screwdriver. If you don't have a keyboard for reference, piano tuning apps are available for phones.

 

[rich c]

Did you check the fork slots? Correct placement of washers, maybe the safety washer, etc... Suspension fork? Could need a rebuild. Can't be a brake problem, has to be a mechanical or adjustment issue

 

[Sierratim]

Please help me understand this... if the headset needs servicing (I really don’t believe it does) how could that cause the wheel to tilt to the left when braking?

The 1” movement is my perception of the amount of movement when I’m moving fast and apply the front brake. It’s my 3rd bike with disc brakes and I’ve never seen (or at least noticed) this kind of thing before.

It‘s a 2019 Giant Explore E+1 GTS, bought new in late fall last year and not ridden during our winter (snow) or during lockdown. The bike has about 1500 km on it now.

A loose head set would allow the fork to move in all directions, but as I mentioned 1" movement is a lot. I do think it's more likely the hub. The pushing side to side check I recommended would quickly help confirm this.

 

[Mtl_Biker]

A shimmy is an uncontrolled oscillation. It happens on some bicycles, often going downhill at speed, but it can happen on flat ground as well. I am merely thinking out loud that perhaps you are experiencing the onset of shimmy without it becoming an actually shimmy where the wheel moves both left and right. But generally shimmying does not occur during braking, at least not that I have ever heard of.

Thanks for explaining that.

I may have found something... This morning before leaving for work, I tried applying the brakes and moving the bike forwards and backwards... no slop and nothing loose in the headset that I could determine. But... I also found that I was able to wiggle the front wheel left and right seemingly around the axle. I had to use a fair amount of pressure to see this. Looks like the bearings might need adjustment. So I took the wheel off and brought it to work with me. As soon as I have a bit of free time (going to be busy today for me) I'll take a closer look. But I realize I don't have any of the thin wrenches here that are needed for bearing adjustment. At least I should be able to see if that's the problem. Then I'll bring in some wrenches tomorrow. I'm encouraged though that this might be the issue.

I'll report later.

Thanks for your help.

 

[Mtl_Biker]

I would turn the bike upside down and check the wheel bearing. With the fork frozen by the ground, the wheel should be able to be tipped no more than 1/8" by pulling on the tire.
If more than that, it is possible the wheel nut is loose, or the cones holding the balls in the race are loose. Or perhaps some balls are missing.
I'd also check the spoke tension. On the 26" wheels I own, properly tightened spokes ping about F4 (piano note) when tapped with a screwdriver. If you don't have a keyboard for reference, piano tuning apps are available for phones.

Based on what I found this morning, (see my last reply to Nova) it just might be the wheel bearings. I brought the wheel to work with me and will check it when I have a bit of free time. But not playing any musical instruments or reading music, I doubt very much that I'd have the ability to tune the spokes based on how they sound when pinged.

I'll report back later when I've done some closer checking.

 

[Mtl_Biker]

Did you check the fork slots? Correct placement of washers, maybe the safety washer, etc... Suspension fork? Could need a rebuild. Can't be a brake problem, has to be a mechanical or adjustment issue

That was the first thing I checked. But now I think it might be the bearings - adjustment.

 

[Mtl_Biker]

A loose head set would allow the fork to move in all directions, but as I mentioned 1" movement is a lot. I do think it's more likely the hub. The pushing side to side check I recommended would quickly help confirm this.

The fork is not moving at all. But your suggestions have worked out for me (Thanks!) as I think it's the wheel bearings. With strong pressure on the bike and the brakes applied, I found the wheel would "wobble" side to side. I brought the wheel to work with me today and will check it carefully when I have the time. Unfortunately though, I forgot to bring the bearing wrenches (flat wrenches) I have with me so I won't be able to adjust the bearings until tomorrow. But at least I hope to be able to pinpoint the problem.