Hackman61

Ok fellas....I have a 2013 Cannondale Synapse that is giving me fits. Well, fit. My front wheel runs true, smooth and with zero issues on the stand. When I get on for a ride, the front wheel grinds. It's not the brakes rubbing, I have plenty of clearance between rim and pad. (Rim brakes). The wheels are only a few months old with maybe a 3-400 miles hundred miles on them. I get off the bike, spin the wheel...smooth and silent. I get back on and the grinding/gritty sound begins. It happens when coasting an no pedaling so I know its not the drivetrain. I've checked the fender and I have clearance between the 28mm tire and the PDW fender. I took the axle out and checked the inside of the hub for dirt. It looked clean. Put the axle back in, wheel back on, spins clean. Get on the bike and the grinding/gritty sound begins. I'm at a loss. I will probably end up taking it in to the LBS but I really would rather fix it on my own. Any helpful nuggets of wisdom from you folks? I'm all ears. Thanks in advance for any help.

Litespud

bearings were smooth and without play when the wheel was out of the frame. Putting it into the frame and clamping it either with axle nuts or QR will possibly over tighten the bearings. You need to set them slightly slack so they’re just right when clamped in

Hackman61

Took off the front fender. It had some crud up under it but not a lot. Got back on the bike and the sound is gone. For the life of me I can't understand why it would make the noise with me on it vs a clean free spin with me off of it. Doesn't seem like there should be that much flex to make it rub. I still want the fender on it given where I live, PNW, but can't ride with the noise. Anything other than smooth and quiet drives me crazy. Anyone else like that?

Andrew R Stewart 

Sometimes riad stuff gets caught up in the fender, the brace clip and the frame clips/mounts are the usual spots where bits of leaf or whatever can stick, hang down and touch the tire. I don't know if this is what happened for you though. Andy

Hackman61

Thats where the crud was accumulated, right at the brace clip.

dedhed

Does it sound like it may be some sort of air flow noise or strictly "mechanical" sounding?

CliffordK

It sounds like the OP found the problem.

The clamping issue with tightening the bearings is QR issue because the QR will compress the axle.

The bolt on wheels don't compress the axle.

Hackman61

Sound was more of a gritty or lightly grinding. The removal of the fender appears to have made the noise go away. so far.

Litespud

As I understand it, the compression is on the cones, not the axle. How does external compression exerted by the QR differ from that exerted by nuts?

Andrew R Stewart 

The way it is that I have been told, by more than a few smarter than I, is that nothing "compresses" within the QR axle. It bows and this is what narrows the distance between the two cones (and thus getting preloaded). With axle nuts the "compressive" forces are contained between the outer axle nut and the locknut/come pair. The axle's central section has nearly no stress on it. Andy

sweeks

This is correct. Steel is an elastic material, and within certain limits can have its dimensions altered by compressive or tensile forces. Just as spokes elongate (elastically) under tension, hollow axles can be shortened under the compression of a quick-release skewer. The decrease in length isn't much, because the axle is a pretty beefy piece of metal compared to a spoke... but it happens. This was discussed in THIS THREAD.

An alternative hypothesis is that the axle doesn't actually compress, but rather "bows" (flexes), causing the bearing races at opposite ends of the axle to deviate from parallel planes and cause binding. This adds needless complexity to the explanation because, as the hypothetical bending occurs, the axle gets slightly longer (stretches) on the outside of the curve and slightly shorter (compresses) on the inside.

Bolt-on axles are different because each axle bolt slightly stretches the axle, but only between the locknut and the axle nut. So there are two short sections of the axle under tension (in the dropouts), and the remaining axle is unaffected.