Beneficial Ear

I can feel a vibration in my pedals under hard (and not so hard) acceleration as well as fast pedaling.

This bike is new (to me) and I do not remember this being the case when I first rode it... however, right after I bought it I did try to power up a steep hill in a gear that was too tough after stopping @ the base. Upon getting stuck/trying to push on, the chain slipped. I hopped off right after that and walked to the top... shortly thereafter (2 slow blocks) was @ the train. I had gotten a decent feel for the bike thus far, this happened @ about mile 10.

My riding weight (jacket etc) was around 225, and I was pushin pretty hard with no pedal movement right before the chain slipped, if that gives an idea of the forces involved.

On the ride from the train to my final destination I started getting on it and noticed a vibration in the pedals upon acceleration, it stopped when I stop pedaling. I have since changed to smoother bearing'd pedals and this made no difference.

Holding the bike in place and pedaling by hand I can feel the vibration as well, and it seems to be involved with the crank in some way as it is definitely not chain rub and it doesn't "feel" as if its coming from the cassette/rear derailleur.

There is, however, no play in the crank that I can feel, if any its very subtle. Also no squeaking, but I can subtly "hear" the vibration when I lift the bike/pedal by hand.

The best way I can describe the feel of this problem is at first pedaling felt like riding over a smooth freshly paved road - now its more like riding over rough cobblestones, though not quite THAT big of a difference.

I'm relatively new to this so I'm not sure exactly what I'm looking for/what could be replaced - (one of) my LBS's said nothing was wrong, apparently my KHS Flite 220 is not "high end" enough to pedal smoothly - I take this as the same elitist BS I've heard from them for years as they try to get me to spend $1000 to get a bike that has the same components as what I have but has a name they prefer looking at...

I'd like to at least diagnose this problem myself before taking it to a different LBS to hear what they have to say... ideally I'd like to fix it myself if no special tools are required, I do have the allen needed to pull off the crank arms, but I have yet to go even that far.

For reference, this is the product spec page for my exact bike:
https://khsbicycles.com/05_flite_220_10.htm

Much thanks!

Airburst

Does this happen in all the gears, or just certain combinations?

How long have you had the bike, and roughly how many miles have you put in, with what lubrication/maintenance?

You'll need more than an allen key to remove the crank arms if they do have to come off - they have to be removed with a crank puller. However, you may not have to.

pierce

the problem also could be in the pedals themselves. cheap pedal bearings fail easily and run rough. usually this would be unequal, you'd feel it more under one foot than the other.

re: pulling the cranks, also see this.
https://www.parktool.com/blog/repair-...e-spindle-type

Airburst

He's changed the pedals to some which were smoother, which didn't help.

pierce

ah, I missed that.

ok, another thing to try, easier if you have a chain punch, or your chain has a release link... take the chain off the bike, or at least off the chain rings (start with the front derailleur in the lowest/smallest chainring, then take the chain off that small ring, and put it against the bottom brakcet such that it clears the chain rings... this isn't always possible), so the cranks can turn without the chain. sit on the bike, holding onto a pole or door frame or something, and put all your weight on the pedals, and turn them slowly around. feel your grunchiness now? if so, its almost certainly the bottom bracket.

while you're there. put one pedal forward and the other back, so both crank arms are horizontal, and putl all your weight on the pedals, even bounce your weight a little. now flip the crank around so the other crank arm is forward and horizontal, and bounce your weight again. if you feel a creak or crink or klank or whatever, maybe just once each time you reverse the pedals, then either one of the crank arms isn't secure against the bottom bracket, or the BB itself is loose.

if you feel roughness without the chain, I think the next step is removing the crank arms, and pulling the bottom bracket out. its probably a UN26 shimano cartridge bearing. it might just be loose. your bike almost certainly uses 'british 68mm' bottom bracket, probably square shaft, but you'll need to know the correct axle length. I would replace it with a UN55 or whatever (52, 56, all about the same). these are better bearings, and only cost $20 or so.

doing that requires special tools, but a bike shop generally won't charge too much for this job, its maybe 30 minutes max.

rydabent

Try cleaning the drive train. Clean and lube the chain. There have been times that I have noticed "vibration" when riding. Lubing the chain has taken care of it.

A second answer is the sprockets and or the chain is worn.

xenologer

Sounds to me like you have a worn out drivetrain.

chain slip under load is a red flag for this

likely some cogs are more worn than others, thus not felt in initial test ride, but more apparant now that you've had time to shift into various other worn gear combos

replace the chain and cassette with new ones.
in severe cases of wear, chainrings too, but wait and see if the former is enough


Not an unexpected situation at all given this is a used bike.

FBinNY 

There will always be some vibration in a chain drive, though a better chain oil will mask it. Vibration tends to be greater with smaller sprockets, and gets worse with chain and/or sprocket wear. As a chain wears it's pitch increases and as sprockets wear their effective pitch decreases. This sets up a mismatch in pitch, analogous to using a close metric screw with an inch nut. Within reason the chain will continue to transmit power, but after wearing too far tend to ride out on the sprocket teeth and slip over the top.

The firt thing I'd do is get out a 12" ruler and measure the chain for stretch. If 24 links (25pins) measure 12 1/8" or more apart that accounts for the problem, and your chain is toast. Unfortunately odds favor that you'll need a new cassette (or freewheel) as well. Buy a new chain, and see if it'll run, but don't be surprised if it skips worse than the old one. If so, either replace the cassette, or go back to your old chain and live with the vibration a while longer until you're ready to replace both the chain and cassette together.

A bit of sad news. Even a new chain and cassette may not feel silky smooth because your chainrings are also worn, but it shouldn't be intolerable.

pierce

yes re chain, but no re sprockets. the pitch stays constant as long as the teeth are evenly worn. what kills a sprocket is when the teeth get scalloped and rounded off. a stretched chain puts ALL the force on one tooth, since the next link is loose on the next tooth, this greatly accelerates the wear on said sprocket teeth, and eventually leads to the chain links skipping on the rounded off sprocket teeth.

using the largest chain-ring practical for the gear range you are in greatly helps this. the larger chain ring sends less force down the chain, and distributes the wear over more teeth. larger chain ring also implies larger rear cog (at the same effective gear ratio), so this applies doubly so.

FBinNY 

You'll note that I said effective pitch of a sprocket. It's an important distinction because as sprockets wear the depth of the root increases, this allows the chain to ride lower where the pitch is shorter.

BTW- the oft forgotten roller wear of the chain has the same effective. It doesn't change the pitch of the chain the way pin wear does (stretch) but allows the chain to ride lower on the sprocket, which has many of the same effects.

alcjphil

As was just pointed out, Roller wear is also a factor to be taken into account. Simply measuring 12" of a chain doesn't take roller wear into account. A local bike mechanic showed me a little trick. Put your chain on the big ring. Grasp the link that is at the front of the ring and pull it forward. According to him, if you can see more than half of the tooth that was behind that link, it is time to change the chain. The beauty of this test is that it takes stretch AND roller wear into account.

mtbikerinpa

I am a fan of the Prolink chain gauge for testing the roller/chain wear. It's only $20 if you go to buy it or free for most shops to check it, which only takes 30 sec to look. If they don't check it free go to a diff shop. I've had quite a few times where I thought it passed the ruler/external test and it ended up missing the Prolink test. It took a little faith the first few times when the bike was noisy but not slippy(I tune a lot of spin bikes), but replaced according to the guage it worked perfectly and eliminated the noise/issue.

FBinNY 

I use the same test all the time, but it also mixes chainring wear, so unless either the chain or chainring is new, you don't have a definitive answer on the other. BTW- based on experience, I allow 1/4" of daylight under a new chain as a warning sign for chainring wear.

For chains I still prefer to measure stretch, and do a visual exam for roller play.

Beneficial Ear

The bottom bracket is perfect, in fact I'm amazed at how well the cranks spin without the chain. No wiggle at all, totally solid and keeps spinning something like the wheels do - if I can get this thing feeling anything like that with the chain attached I'll be in cycle nirvana.

The vibration is most noticeable on the big front cog, 2 small rear cogs... after a 60 mile trek today the vibration is significantly worse - now its painfully obvious and shakes the bike a bit on the small rear/big front cogs. I can feel a vibration on all the rear cogs to some extent, lesser with larger. This is pedaling by hand/holding the bike.... the vibration is most noticeable when alot of torque is applied in general, once the pedaling speed goes up its not as significant but definitely does not totally smooth out.

I see some broken teeth on the rear cassette, only on the 2 smallest cogs. 25 pins = 12" so I don't think the chain is stretched, and I don't think its too long either.

New cassette time? Is it possible it can be anything else?

I'm not sure what the rollers are, or how to check to roller play.

FBinNY 

Your description is exactly what a worn cassette would act like, with the smaller sprockets having more wear and vibration than the larger ones.

OK, I gather you bought the bike used. It's possible that the cassette is on it's second or third chain. It's kind of hard to explain how to visually identify a worn sprocket, especially because modern cassettes look worn when brand new.

But you can try the pull the chain away at 1/2 wrap method to gauge the condition of your cassette. Since the chain seems OK, if it can pull away anywhere close to where there's 1/4" daylight below, then the next step is to try a new cassette (or freewheel).

When you switch the cassette, save the old one just in case that isn't the problem.

Beneficial Ear

Any cassette suggestions? I've broken many a low end cassette/freewheel in my bikes and I want something that will stay in one piece, last, and feel solid and smooth under torque. I can do up to about $100 for this + chain... I definitely want to keep the 11 gear though, I love to mash it on steeper downhills.

pierce

if you're breaking cassettes, you're doing something wrong.

'mashing', yup, thats what they call it.

spin, don't mash.


that said, the Shimano HG50 cassettes have never given me any grief. I'm using a 13-26 8-speed on my hybrid.

FBinNY 

IME it's pretty hare to break a cassette sprocket in normal use. They wear out. If teeth are breaking something is wrong. I suspect you're shifting under heavy power, especially since you describe yourself as a masher. Whatever cassette and chain you choose, go easy on the pedal pressure through shifts and you should be fine.

I should add that small sprockets never feel as smooth as larger ones, especially under load. Read up on chordal action, and you'll see that it gets more pronounced with fewer teeth.

ThermionicScott 

Here's another thought, since it's something I've observed in my bikes -- is there any wobble to the chainrings? Even with brand-new chainrings and cogs, you can get that awful rumble if something in the drivetrain is causing the chainrings to run out of true. I suspect it's because the chain alternately has to ride up each side of the chainring to stay meshed.

https://sheldonbrown.com/straighten-chw.html

FBinNY 

I strongly doubt that chainring wobble is the problem, unless it was enough to cause chain rub of the FD cage, which the OP has ruled out. OTOH, if the vibration has sort of a rhythmic snoring sound, then he should check for chain/FD rub.

The reason I doubt that crank wobble is a factor is that the chain coming off the outside of the cassette will always rub the inside flank of the chainring's teeth. That's normal, and the wobble would have to be beyond the limits imposed by the FD for anything to change.

BTW- there still remains the possibility that the problem is worn/pitted BB bearings. The only thing pulling me away from that theory is that the OP says the vibration varies with gear selection, and that the cassette shows some visible damage. But it might simply be that he's pedaling harder in those higher gears.

ThermionicScott 

I had the worst problem of it on my fixed-gear. It was the bane of my riding existence until I got the chainring to run truer -- first, by finding out which of the four positions on the spindle ran straightest, then by tweaking the crank spider a little so that there was a minimum of runout when the chainring was mounted. (Radial runout was never very bad.)

I think things might be different between simply running derailleur gears out of alignment, and adding in a wobbling chainring, because in the latter scenario, the chain has to continually migrate from one side to another. IOW, when the chainring wobbles to the left, it sets up the chain to grind when it wobbles to the right.

As another example, I replaced the BB spindle on my main touring bike this summer, and didn't pay much attention to runout after mounting the crankset. I found later on Ragbrai that lots of gear combinations rumbled objectionably, not just those on the smallest cogs. I was bummed that something had already gone wrong with my bottom bracket, but then noted the chainrings were wobbling a bunch. I worked through the process of finding the best position on the spindle (this shouldn't be an issue, but I guess the spindles they still make aren't perfect), then tweaking the crank spider a little. It made a world of difference on that bike and everything was much smoother after that.

FBinNY 

I can understand that, but a fixed gear is different than a derailleur bike. The width of the FD cage limits chainring wobble to about 2mm or so TIR. Anything more and the chain would rub the cage on one side or another. The OP says there's no rub, so we can safely assume that the total wobble is within that 2mm limit.

With the chain coming at an angle from a sprocket 10mm to the side, another 2mm isn't going to make a difference.

ThermionicScott 

In my case (second example), just less than enough wobble to rub the FD cage did make that difference, and because the chain angle varied throughout the pedal stroke. Not trying to argue here , but I'd be interested if that might be happening on the OP's bike before trying to dismiss it as a possibility.

FBinNY 

Anything's possible, and it takes a second to check, so the OP might as well rule that out before spending dough.

Chainring wobble is easy enough to check by looking from the top and watching the chain clearance vs. the FD cage.

Beneficial Ear

Wow I "feel" that graph exactly. Very interesting information.

I'm not shifting under heavy power, I've made that mistake in the past and its how I destroyed a cassette on my old mountain bike. However, the "resolution" to this has been to make less shifts when sprinting, and I sprint alot trying to keep up with city traffic (and generally I do keep up). So generally I start on a smallish cog (good to 18mph or so) to avoid the shift under power... this is how I bent my old bikes axle and ran through 4 sets of cheapy metal platform pedals, but other than switching under power/breaking teeth I can only guess its get better components or slow down... and I can't slow down