msu2001la

I have a brand new bikesdirect "Uno Outcast Pro" bike that has a single speed 16T freewheel drivetrain.

Save Up to 60% Off Motobecane Cyclocross Singlespeed Fixie Bikes - UNO OUTCAST PRO Track | Singlespeed Gravel Cross bikes | Save up to 60% off new bikes (bikesdirect.com)

The bike is making a clunking noise when pedaling that sounds like it is coming from the rear hub. It was doing this out of the box. The freewheel seems to spin smoothly when coasting and only makes this noise when applying power. I've removed the rear wheel and the crank spins freely and smoothly, so I'm pretty sure it's not that.

This frame has a horizontal sliding rear dropout to adjust the chain tension - I've got it inserted to have around 1/2" of play on the chain when pressing down on it.

Any thoughts on how to solve the clunking noise? I'm not opposed to replacing the freewheel if that solves it, but I wanted to check with others first before buying a new one. (And I also have to buy a removal tool)

msu2001la

Also similarly related - sliding horizontal dropouts and hydraulic disc brakes. I didn't really think about how this would work before buying, but there's a lot of moving parts here to get aligned perfectly.

I had to loosen the rear caliper just to get the rear wheel out because the rotor wouldn't clear the caliper otherwise. Getting it back in and aligned was a bit of a challenge with all the moving parts - basically having to eyeball the wheel alignment (while getting chain tension roughly correct) and then re-adjusting the caliper to match.

I haven't owned a single speed bike since having a BMX as a kid, so maybe there are some tricks to this that I need to learn.

Iride01 

The chain isn't too tight is it?

msu2001la

How tight is too tight?

It actually seems to make less of the knocking noise when tighter, but now I'm worried it's too tight.

Iride01 

They say you should easily be able to lift the chain a half inch. But I'm just spouting off things I've read here on BF. No actual experience with them since I was about 7 yo.

Someone here had a new or nearly new chain with a link that was frozen up and made a unusual noise while pedaling.

mrv 

1/2in of chain sag seems like a lot to me.
I typically get the chain as tight as possible. I’m sure that’s wrong for one reason and another. But seems like things loosen up on their own.

I’ve noticed my fixed gear clunking- but then I also noticed the chain was loose/sagging. So I’m assuming I need to tighten the drive train to fix the noise.

any chance you have a different freewheel you could try?

FBinNY 

First double check that chain slack is adequate. Off the bike turn cranks while watching or feeling the lower chord. You want vertical play at the tightest spot. That's important because half an inch at the slackest spot may not be enough.

Next, consider your pedaling style and rhythm. Often folks riding gears lower that they're used to slow when cranks are vertical, allowing the wheel to overrun the sprocket. You then get the clunk when it re-engages on the downstroke.

Last, get a good sense of the rhythm and timing of the clunks. Are they random or rhythmic, and if so, sync'd to the wheel or pedal, and if the pedal timed to what part of the cycle?

FWIW the freewheel itself is the least likely cause. Once you start pedaling the freewheel engages and locks onto itself as if a single block of metal. It will only unlock when the wheel overruns the sprocket. (coasting)

3alarmer 

.
...I had a single speed Bianchi, with a flip flop rear hub for either fixed or freewheel. It had a similar "klunk" that used to happen intermittently, when using it in the freewheel position. I was able to narrow the source down to the freewheel (which was not a great quality freewheel to begin with), by flipping it over to the fixed gear position, when the noise disappeared. In your case, with the setup you have, I don't know how you would do it, without swapping out a better quality freewheel to see. FWIW, even though freewheels are rarely the source of such noises, the quality of some of the newer ones is so poor that they do become a possibility.

I can't imagine they used a high quality freewheel on your bike at that price point.

With the whole disc brake setup you have going on, I'm not sure you can just swap in another wheel as a test. Good luck with it.

DorkDisk

Sliding dropouts with fixed mounts for calipers sounds not too fun.

Since rotors are involved, don't rules these out; they can make weird noises that sound like something else. The rotor might spin clear in the stand but rub under power.

Rotate the wheel 1/8 at a time and clamp down the pads by hand and feel if each travels the same distance (centered). Adjust the calipers / bend the rotors to make them truer.

msu2001la

I have a new freewheel on the way and it should arrive today. I am suspecting that there is a small amount of play in the stock freewheel (which I agree is the lowest possible quality) that is causing the noise. A new freewheel was relatively cheap and will at least rule it out.

A few reviews on this bike mentioned similar clicking/clunking noises that were solved by swapping out the freewheel, so I'm hoping this solves it.

The noise I'm getting is definitely not the brake rotor rubbing (they rub too, but that noise is distinctly different and solved by fussing with the caliper alignment).

That said - I would discourage anyone from buying a single speed bike with sliding dropouts and disc brakes. I don't know what the correct way is to design a single speed frame with disc brakes, but this doesn't seem like it. Every time I remove the rear wheel on this bike I have to loosen the brake caliper (the rotor won't clear the caliper otherwise). When I put the wheel back in, I have to re-align it several times to get the chain tension set (and wheel straight) and then similarly re-algin the caliper to get it lined up and not rubbing. The bike also has fenders installed now, so that just adds another layer of complication, as I have to loosen the fender mount to allow enough room to slide the rear wheel out of the dropout.

Thankfully other than changing flat tires, I don't think I'll need to remove the rear wheel very often.

79pmooney

1/2" slack in a fix gear/single speed chain is normal and healthy. It should never go tight. (Pedal several chain revolutions to make sure. Both chainrings and rear cogs can have asymmetry. Until you line up both you haven't seen the tightest the chain will see.)

Clunking in a fix gear with chain slack - probably less than smooth pedaling style. When you get lazy and pedal slower than the bike, the bike will remind you quite abruptly. And with a clunk. Incentive to up one's level of pedaling grace. Says he who has ridden those things almost 50 years and more than half way to that orb in the sky. Still gets visited by 'the clunk" every once in a while.

79pmooney

Strictly my opinion here - single speed or fix gear and a rear disc brake? Why? Rear brakes at best do 1/3 of the total work to stop you and zero in the ultimate hard stop. Any decent rim brake will do just fine. Pick one that feels like the disc front. Rim brakes play nicely and easily with single speed wheels using ordinary dropouts or track ends to adjust chain slack. A real point of the fix gear/ single speed is that revered saying that they exemplify so well. KISS - Keep It Simple Stu... A mantra of many successful (and still alive) ocean sailors. A system that requires an exact match in location between the rear wheel and anything on the bike? In 1/1000ths of inches? When you are sliding that wheel around to adjust the chain? (Scratches head) The crude axle and track nuts bikes have been using for over a century are just about perfect for the job. Yes, exactly where the wheel lands varies. So does how straight it sits. But it really doesn't matter unless you are OCD, vain or have to submit to some inspection. (I've been doing those sloppy wheel fits for - well see that post above - a long time.)

alcjphil

The correct way to design a single speed bike with rear facing fork ends like yours is to locate the brake calliper on the chain stay rather than on the seat stay as yours has been done. That way the rotor can slide straight back without having to loosen the calliper as you have to do

3alarmer 

.
...despite the many references to fixed gear, this bicycle is not one. Mentioned for clarification as to the various diagnoses offered. The OP offered a link to the bicycle in question.

choddo

I don’t think that looks like any cyclocross bike I’ve ever seen before. Can’t see Wout van Aert throwing that around in the Belgian mud 😁

msu2001la

Confirmed - it was the freewheel. I replaced it yesterday with a new one and the noise is gone. The other freewheel seems to have a small amount of lateral play between the bearing and the sprocket.

3alarmer 

...thanks for following up in the thread. That was the issue with the one I had, too. It was made louder because the larger frame tubing in the Bianchi Pista seemed to amplify the noise. I guess maybe it was the flopping back and forth of the drive portion of the freewheel, as it rotated under tension.

oldschoolbike

I realize I am in this thread late, but it struck a cord with me as I struggled with knocking myself. It's not chain slack, it is the outer body knocking back and forth on sloppy bearings as chain tension orbits the cog. The body does not lock up under such rotating force, in the frame of reference of the sprocket.

My offenders were both Shimano. I considered opening them up and lapping the outer race/lockring as I used to do with multi freewheels, but figured I might bend something and just make matters worse. I gave the freewheels away, so very little guilt about passing on junk. As a heavy user of single freewheels, I needed a better quality item than Shimano. ACS Crossfire did not knock, but had other issues. Sturmey-Archer single freewheels were fine. They look good, don't skip or knock, and get smoother with use. So far so good on durability, but I use good chains too.

Single freewheels in frequent use have to be very good quality. Sturmey-Archer (probably SunRace) seem to be good enough, but maybe I will treat myself to a White Industries for my birthday

oldschoolbike

msu2001la

Thanks for the addition. When I was looking for a replacement freewheel I saw the White Industries option and was mildly intrigued - I've heard good things about their hubs. At over $100 though, it seemed a tad excessive for a commuter bike.

I found the Origin8 freewheel ($50) and was intrigued, then read reviews about it being really draggy and decided I didn't need 108 points of engagement while riding to work.

The freewheel I did buy came from Amazon and cost $17. The manufacturer name on the side is "DnP.". I have no idea what the quality is, but better than whatever Bikes Direct was installing on these bikes. Considering the low cost, I assume I'll be replacing it at some point in the future. Depending on when that is, I may consider buying something nicer like one of the brands you mention above.

3alarmer 

.,,,the Sturmey Archer branded one he's talking about is about that price. I think it's made by SunRace.
For what they charge for stuff, SunRace is usually pretty good quality (IME)

Russ Roth

you DNP is probably the same quality. The freewheel on mine was perfectly fine and coasts forever but the pedals failed after less than 5 miles. First ride on it was a 12mi trip, after 2mi the nylon started cracking, at mile 5 both had the nylon pedals crack off the spindles which made finishing the ride a little rough. I've seen it happen with old pedals after lots of use but never new ones. Replaced the pedals and find it to be a great commuter.