There is a grinding feeling at the end of my pedaling at high speed

Question

I bought a road bike about 6 weeks ago, but I just only realised it now that at the end of my pedaling (when either foot pushes down), I can feel a bit of a drag/friction/grinding on either pedal. I don't know what's the cause. It just feels unsafe, like something's about to come lose.

The closest thing to describe this friction/grinding feeling is if you imagine going on to a grated bridge. It feels like that.

I noticed that I only feel this at high speed and high gear (about 20+kmph and ~50 cadence). I can't pin point what's causing this because I can only feel it when I'm travelling at high speed and so it is really hard to try to look to see what's the cause.

Is it "normal" to feel this "friction/grinding" at high speed. This is my first road bike so I'm not too familiar on what's "normal".

Could it be due to low/high tire pressure? The tire says 130 PSI... but my pump gauge is broken so I just put as much air as I can and as much as the tire can take before it won't take anymore (using my body weight to pump the last few inches of air into it).

What should I be looking for to troubleshoot this problem?

Update

I've put the bike on an indoor trainer. I took off the pedals and then apply pressure to the cranks by hand. I can still feel a "grinding". So not the pedal.

I then took the chain off to see if it's somehow related to the chain tension. I spun the crank slowly, and I can feel a slight grind - not very noticeable, but it has the same rhythm of the grind when pressure is applied. So it's not the chain tension, it has something to do with the crank.

That is, the grind is more noticeable when pressure is applied to the crank. It might have something to do with the bearings of the crank. But because this is a new bike, I'm questioning if this is suppose to be normal and whether I should put up with it?

When you spin the crank should it be completely smooth without any noticeable grind? If so then I need some tips to rectify this problem because I've never worked with a bike before.

More update

After weeks of inquisitively monitoring the bike, and doing bits of adjustments. I re-greased the pedal bearings, which helped. I can only feel the vibration slightly at high speed and when applying pressure. Not as bad as before. It appears that the pedal bearings were either too tight or too loose which caused a vibration when pedaling. Now the problem still persist, but slightly less so than before.

I cannot regrease the bottom bracket bearings because it is a Shimano Hollowtech and so would mean I have to buy a new bottom bracket if it is the cause.

However, I've done more research and found that the wheels can be out of "true" and cause a wobble/vibration when riding at high speed. I spun the wheels and monitored the brake calipers. My back wheel is definitely way out of true. It appears to be rocking from side to side about 1mm apart. So I've ordered a spoke wrench which should arrive in a week or two in hope to "True" the wheel to fix the problem. Will update when I've trued the wheel.

BTW, I've learned my lesson not to buy anything bulky/expensive online, because it's hell when something goes wrong.

Answer 1

I would say: pedalbearings? Seems that when you apply pressure, the bearing gets pressurised, causing this "rough" feel.

Answer 2

A grinding feeling can be caused by all sorts of things. It could be a chain in need of lubrication or replacement, damaged rear derailleur pulley wheels, bottom bracket bearings grinding, lose cranks causing the innermost chainring to rub on the chainstay, misadjusted front derailleur rubbing against the chain, misadjusted rear derailleur, the tire intermittently rubbing or something else.

To begin, move the chain out of the way so that it is disconnected and not interfering with movement of the cranks. If there's still grinding without the chain attached then it's probably somewhere with the cranks, chainrings and bottom bracket. Are the cranks firmly attached to the bottom bracket spindle and do they move together if wiggled? If not only of your cranks may be loose and if it's the drive-side the chainring could be rubbing. If you wiggle the cranks do they move in any way other than the spinning that they're supposed to do? That would mean that you very likely have a problem with your bottom bracket.

If the chain needs to be attached for the grinding, is the upper pulley of the rear derailleur causing strain on the chain against the sprockets on your cassette or freewheel? That would mean you should adjust your rear derailleur. Does it matter which gear you're in when you experience the grinding? If the gearing matters, do you notice any rubbing of the chain specific to that gear, for example against the front derailleur cage?

If the gearing doesn't matter, does each link of the chain move freely or do some bind? It's possible that some links could be roughly passing through the rear derailleur or elsewhere and causing a grinding sensation. Does the grinding happen only when pedaling forward (i.e. the wheels are turning)? If so, does any part of the wheel or tire rub against the bicycle?

Answer 3

Sounds like the bottom bracket bearings are worn or failing. The bearings could be pitted or have become oval over time giving you a tighter/rougher feel in the pedaling stroke. This will become worse as time goes on, so a new bottom bracket is advisable.

Answer 4

If there is a grinding in the crankset with the pedals and chain removed, it most likely looks like you bought a bike with a bad bottom bracket. Modern bottom brackets are sealed cartridge units which turn smoothly with no grinding or free play (due to preload). Any grinding means that there is debris inside the cartridge (such as metal shavings), or poor quality balls (not almost perfectly spherical with a ridiculous tolerance, as bearing balls must be) or imperfections in the bearing surfaces over which balls roll.

But, one small thing check for is: are any of the chain rings coming into contact with the chainstay member of the bike frame? That would cause grinding; you'd be surprised at how you can miss this kind of detail if your focus is somewhere else. Rings rubbing on the frame would be caused by installing the crank on a bottom bracket with too short a spindle length for the frame: incorrect "chainline".

If a ring which is on the verge of touching the frame is slightly out of true, then you can get an inconstant rubbing when when a few teeth make a light contact with the frame, once per revolution; you would feel a light grinding on the bike stand, which might get worse with frame flex (actually pedaling the bike under load).

This rubbing issue is in fact more likely to happen on a road bike, like yours, when the crankset has only two rings, because the inner ring closest to the frame is large (often 36T or more; e.g 52-39 setup). With a triple crank (some road bikes, most mountain bikes and hybrids), it's less likely for this rubbing to occur even with a spindle that is too short, because the inner ring is much smaller: as little as 22T up to around 28T.