I have a brand new '13 Cannondale CAADX Disc Ultegra 54" There seems to be a premature and destructive grinding going on between the hub locknut and the front fork end when the front brake is applied. Photo below.

A chatter/vibration clued me in, and it's not any normal rotor or assembly chatter. It's a fast repetitive grinding/flexing noise, and when speed is reduced enough, you can actually see the fork ends shudder.

Stopping power is not affected, skewers have always been tight (very tight now) but the noise, grinding, and shudder persist. I'm 6', 185 lbs so I'm not a featherweight, and am wondering if somehow this disc and carbon fork combo just went south.

As I mentioned, it's brand new, and it's been in the hills less than a dozen times. I've removed and inspected the front wheel and rotor less than a dozen times. Rotor is true and the Bengal brakes are fine - but somehow the stresses are transferring and twisting the forkend enough to do this damage. Hub is fine, albeit with some visible wear on the knurling/teeth of the locknut.

Outside side nearest to brake/rotor assembly also has a bit more wear than I'd expect from a 2 month old bike, but nowhere near the hub side of the fork end. Thoughts people?

Thoughts? Yeah, get it back to the dealer NOW. Something is certainly wrong and Cannondale should sort it out for you.

Unlike rim brakes, discs apply a significant reaction force on the axle. You can see this if you think of the wheel as a lever with point of contact on the ground, the brake and the axle in a straight line. If the disc caliper is forward of the fork blade, the reaction lifts the axle into the dropout and all is good, If the caliper is behind the blade it drives the axle down, which can be a problem.

You can see this for yourself if mount a wheel loosely, apply the brake and push the bottom back as the ground would when stopping.

So whatever brake you have it's important that the QR is secured more tightly than you might be used to doing with rim brakes. You can also help yourself (if the disc is forward of the fork) by mounting the wheel with the bike on the ground. This sets the axle to the top of the fork slot so even if the QR is a hair loose it still can't move higher.

BTW the same rules apply on rear wheels with vertical dropouts.

Thanks guys, understood about the forces and caliper placement. The skewers have been tight, I even used a better pair of Deore XT and made sure it was a near-painful press to close the damn thing. I am a mechanic, and it's tight, and it's still coming with the funk. The dealer has reached out with photos to Cannondale and I'm hoping for some insight or some Warranty action. If they replace the fork and perhaps the whole wheel w/ rotor, the question is, will it do the same thing? Anyone out there with this new 2013 CAADX Disc experience anything like this?

OK, I'll go out on a limb here, and say this is a perfect example of why disc brakes on road bikes are problematic. What follows is opinion, but it is based on experience.

First of all, Cannondale chose to best design practices and mount the brake behind the fork. (Yes, I know they're not alone here, but this decision compounds the complications that follow). Add to that, it doesn't appear that they did anything to stiffen the curved blade fork. So when the front brake is applied hard one fork blade flexes under the stress, moving the tip with respect to it's partner on the other blade. That makes the axle work in the tips, chewing into the metal.

These are the kinds of issues that led to adoption of through axles on high performance (especially DH) mtn bikes.

IMO, there is no cure short of replacing the fork. If the brake were forward of the blade, you might have gotten some improvement by using smooth axle faces, but I don't think that's a safe option for this bike.

BTW- expect more of these kind of issues as makers start fitting disc brakes to road bikes without doing their engineering homework.

On this link in posts 5 & 6 you can see the effects of a fork that couldn't handle the power of a disc brake under heavy braking.

https://www.cpsc.gov/en/Recalls/2013/...Bicycle-Forks/

It isn't only a matter of breakage, but a total revisit of strength and stiffness in the forks design.

A rim brake exerts a braking stress of roughly double the braking G-force applied at the tip with fulcrum at the crown. The normal taper and oval section of a typical fork blade handles that fine.

However with a disc brake, in addition to those forces, we have the local stress imposed down at the caliper. This is much larger than 2G since the rotor diameter is smaller than the rim. That has the lower end of the fork stressed highly in a way that doesn't happen with rim brakes. Even if the fork can handle the load, there's still lots of deflection at the tips (unless the fork is beefed up significantly) which can work a wheel loose.

Beefing up the fork seems obvious, except that without suspension, that would cause negative changes in road holding properties.

Those who don't like disc brakes for road bikes, aren't just retro grouches. They just see some of the complications, and, on balance, feel it's a lousy bargain.

I expect that if and when disc brakes begin to appear on more road bikes, there will be a number of poorly conceived bikes, followed by improved forks that ride poorly, followed by --- you guessed it --- suspension road frames.

There was an old lady who swallowed a fly.....

Resurrecting an old thread here... I have a fairly new 2014 CAADX Disc with what seems to be the same problem (see pic). OP, how did this end up for you?

Given that the OP was last active in Jan of this year, doubt they will respond. For your fork, that's a warranty issue as the dropout has failed, How did this happen? Was is while riding or when the wheel wasn't inserted?

It happened when I was riding but I can't pinpoint an exact moment. When the wheel is off, I'm careful not to rest the bike on the dropouts. Ultimately brought it in to my local shop and had it checked out. They filed down the rough areas and assured me it is safe to ride. I'll keep riding on it for now and watch it closely. The mech did say my quick release was not super tight so I wonder if that had something to do with it.