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Front wheel rubbing brakes

Old 11-27-13, 09:01 PM
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Isaiahc72
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Front wheel rubbing brakes

I have a Raleigh M50dx with some nice Mavic wheels. However, whenever I stand up and pedal hard, the front wheel rubs against the brakes. But when I'm just cruising and slowly pedaling, it doesn't rub. I thought it might be loose spokes but my LBS said that they were fine. The wheel hub seems tight enough. What is it and how can I fix it? Any help would be appreciated
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Old 11-27-13, 09:05 PM
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Greetings, fellow NWA'r.

For how long has this been happening?
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Old 11-27-13, 09:06 PM
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Have you considered fork flex?Perhaps a broken axle?
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Old 11-27-13, 09:12 PM
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I suspect that the bike has a front suspension fork. Assuming that all seems right (true wheel, good hub adjustment, tight QR, brks not too tight or already rubbing) then fork flex is left. And a suspension fork has flex by design. Unfortunately the neat vertical flex (that we call travel) requires some slop between the legs and stanchions. This is why so much expense is spent on stiffer axle/led clamping designs. You can test this easily enough. Have a friend hold a piece of paper between the rim and pads while you stand over the bike, locking the rear brake (so the bike doesn't roll) and torque the handle bars one side down and the other side up (like when climbing a hill). Don't be surprised if the piece of paper gets trapped between the rim and pads and can't be pulled out. If this is happening there's not much you can do other then get a fork (and hub) with a stiffer design. Andy.
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Old 11-27-13, 09:15 PM
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Darn spell check...

"neat vertical flex" should be "near vertical flex"

"axle/led clamping" should be "axle/leg clamping"

Andy.(at least i spell my own name right).
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Old 11-27-13, 11:23 PM
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Ah, right....suspension fork. That's why I'd think, too. Funny. You'd think someone at a bike shop would mention that.
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Old 11-27-13, 11:49 PM
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A brace across the top of the fork-tubes will minimize uneven-compression between the two sides and keep the wheel moving more in vertical plane.
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Old 11-28-13, 08:30 AM
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Originally Posted by DannoXYZ View Post
A brace across the top of the fork-tubes will minimize uneven-compression between the two sides and keep the wheel moving more in vertical plane.
And if the Op's bike has a suspension fork without this brace then it is much cheaper then I cetainly give it credit for. Andy.
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Old 11-28-13, 10:29 AM
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It's a "Rockshox J3". I don't understand how fork-flex could cause the brakes and wheel to rub considering that the brakes and wheel are both attatched to the lower portion of the forks
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Old 11-28-13, 11:19 AM
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There is flex within any structure. With a solid fork the two blades have a high amount of stiffness in their lengthwise directions (since most fork materials are pretty much compressionless). So with a solid fork blade any flex is largely that of side or fore/aft directions. And i think we all know that these directions need to be limited to a high enough degree so the fork keeps the front wheel pointing/placed in a manor that lend it's self to control and long life.

Now with a suspension fork the blades are designed to flex, or as more people will say "compress". This is not necessarily going to be the same on both sides/blades. If the wheel sees a tilting force (say when the rider presses down on one side of the bars while lifting up on the other end of the bars) then the two sides of the fork will tend to flex/compress to different amounts. Only the top brace and the axle/clamping will resist this. The lower cost forks tend to not have as stiff a brace and also use the standard axle securing designs (that solid forks use). The standard axle securing designs are axle nuts or QR skewers and are only originally meant to hold a wheel in place, NOT keep the two blades/drop outs aligned with each other. Why should the securing design need to do that, after all with a solid fork this is handled by the blades' materials. But with a suspension having blades that can change length the standard axle securing methods are overwhelmed and there is flex between the drop out and the axle (or wheel).

This flex is seen as the wheel tilting off parallel to the fork's center line. Yes, this means that the top brace is bending some what. This means that the drop outs are wiggling to a degree between the axle lock nuts and the securing device (QR or nuts), or the axle it's self is bending along it's length. (This is why suspension equipped bikes see more bearing wear the solid forked bikes do. But that's another topic...)

My experiment was an attempt to see easily and quickly this flex and why it often causes the pads to rub the rim when pedaling or cornering hard. The stiffer axle securing designs using drop outs that better clamp a larger axle (through axle designs) so to counter this flex. They are found on the more expensive bikes typically. A visit to your LBS will offer you a chance to view the increasingly stiffer but more expensive axle/fork designs. And you could preform the paper between the rim and pads test to confirm these designs greater stiffness. (If you can find a rim braked bike with through axle designs. These days pretty much any higher performing mountain bike will be using disk brakes. Although the same issues apply to disk brakes. Just with less distance from the axle to the pads, with disks, there will be less measured amount of movement all things otherwise being equal). Andy.
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Old 11-28-13, 12:22 PM
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You could also replace the axle in the front hub with a bolt on(track style nuts)kit you can get fairly cheap at your lbs made by problem solvers.That will lessen the flex quite a bit,but not get rid of it completely.


EDIT:All you need is the problem solvers axle to match your threading and two nuts.You can reuse the cones and bearings.


EDIT 2:Also,a heavy duty brake booster might help,but probably no much.

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Old 11-28-13, 06:38 PM
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Alright thanks. Is this something I should worry about? Or will it do any damage to any part of the bike besides the brake pads?
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Old 11-29-13, 04:49 AM
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Originally Posted by Isaiahc72 View Post
Alright thanks. Is this something I should worry about? Or will it do any damage to any part of the bike besides the brake pads?
The pressure on the pads will be minimal compared to when you're braking, so don't worry about it.

If it's a rim brake wheel it's possible to have it rebuilt with radial spokes, heads-in, which will make it a couple of % stiffer sideways.
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Old 11-29-13, 08:58 AM
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Originally Posted by dabac View Post
The pressure on the pads will be minimal compared to when you're braking, so don't worry about it.

If it's a rim brake wheel it's possible to have it rebuilt with radial spokes, heads-in, which will make it a couple of % stiffer sideways.
And if the brake rubbing problem was from a wheel that was flexing ON TOP OF the hub (the hub staying stationary, like in a solid fork) then stiffening up the rim/spoke system would help, a small bit. But I think the OP will find that the fork's flex is FAR greater then the wheel's. Andy.
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