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: