Disc brake pulling front wheel towards it
 

Observing my front wheel tonight while I was braking it was noticeably pulling my wheel towards the brake side. Any ideas?

What fork & type of axle ?

Loose spokes ?
Flimsy fork ?
Broken axle ?

Something doesn't sound right. The brake rotor is attached at the wheel hub, so we can discount the spokes and rim deflecting. My guess would be something up with the axle. Is there any side play in the wheel?

Slightly similar topic, I could see my rotor deflecting when I apply the brakes (bike on its workstand). That is cured by re-centering the caliper (loosen mounting bolts, squeeze lever, tighten mounting bolts).

Non-suspension, quick release axle, I don't think that the spokes are loose. It's my Giant Seek 2.

Not that I've noticed, I'll check it tomorrow.

I don't know if it matters, but it is also a hydraulic disc brake system.

Check to make sure the quick release is tight. Front disc brakes put forces on the wheel that want to pull it out of the fork. If you don't already have a good quality enclosed cam skewer, get one. http://sheldonbrown.com/skewers.html

I'll check that tomorrow before I ride along with the side-to-side play.

Cowboy: Beside the enclosed cam skewer suggestion above (I am partial to Shimano, myself), also check to be sure that your axle is not protruding past your dropout. You want the skewer to clamp the dropout not the end of the axle. You also need to adjust the skewer tight enough that it makes a mark on your palm when you close it. Also, while it is unlikely, check to be sure you don't have a broken axle.

But the braking force from the rotor needs to be somehow transferred to the rim/tire and it gets there through the spokes. During braking the hub is torqued (just like your rear hub is when pedaling) which adds tension to the leading spokes and removes it from the trailing spokes. Due to the tension differential caused by the offset in the disc brake hub, it's quite possible that an improperly tensioned front wheel could be pulled off-center when the hub is torqued.

I'd definitely check the quick release first but if no problem was found there I'd move right onto the spokes as the next most likely culprit.

It was the QR having come loose. I tightened it up before my ride and the problem was solved. Thanks to everyone for your help.

Braking force is applied to one side, as it is.

this is a cast alloy suspension fork, right?
standard forks have to up the stiffness to reduce that tendency.

yes I would go thru the wheel and re-tension it tight again, hub, play, at the axle ,

maybe stem clamp is loose, and so the braking is twisting the whole fork
relative to the handlebars..

then if all that is checked thru, then it's just a physics lesson ..

now you know why motorcycles double disc front wheels.

So the question is: do you have a good quality enclosed cam skewer? They're a must for horizontal rear dropouts and front disc brakes. The inferior exposed cam skewers will slip. If you have one, I strongly suggest you replace it. You don't want your front wheel coming out during hard braking!

While the exposed cam skewer may be inferior in some ways, they are lighter and have proven perfectly sufficient on my commuter with a front disc that does 99% of my braking (American Classic skewers). I'll hit 13,000 miles on that bike in another week or two. I personally wouldn't call the internal cam skewers a must for normal duty. The lawyer lips on my fork are huge though :) And downhill MTB'ing might be a different story too.

Wrong, it's a non-suspension fork.

All I had to do was to tighten the QR and the problem was fixed.

It was just the wheel itself that was being pulled to the left. It wasn't the fork twisting.

They're the exterior type cam QR skewers. I think it was just a case of vibrations from everyday riding causing it to work loose.

Both my Hardrock and my Seek have exterior QR skewers. Actually the only wheel on either bike that has an internal QR skewer is the rear wheel on my Hardrock and that's because I changed it out to use my Yakima Big Tow trailer.

The only off road riding I do is when I ride the Pinellas Trail.

This topic got my attention because I have a road bike that does that. The bike pulls a bit to the left the moment I apply the front brake.

What I've found is that since I use two different brake pads, there is some lateral torque at the caliper that gets resolved in the fork legs between the caliper and the axle.

It's noticeable, but not a huge movement, been doing this for years! The QR is conventional old-fashioned closed type, and clamps fully, and the wheel is handbuilt 36-spoke, so nothing flimsy anywhere. Tubing is Ishiwata 022, heavier than Reynolds 531 blades, and I'm only 155lbs.

For a long time I figured the headset must be deformed in some way, but it adjusts smoothly.

Jeez people how hard is this? Is it really worth saving 40 grams to have a skewer that might not hold your wheel in place? Obviously it doesn't, you've found this out firsthand.

Have fun the next time it works loose due to "vibrations from everyday riding."

Sometimes the cause of this is not having the wheel centered in the fork. I have a junky old bike that sets the wheel off to the side when the axle is fully seated in the fork ends. To correct this I have to nudge one side down to get it centered.

As you explain, the different brake pads could be causing this too. Next time you ride check out your front wheel and see if it's centered in the fork.