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| *Vultures Knob>>>Bike Pedals |
My bicycle "thunks" when I pedal. once per revolution. it also "rattles". what is the problem? |
I can actually feel the thunk when it happens. usually when my right pedal is near the bottom of its revolution path. I cycle just in the city. it is my main source of transportation and I am really concerned. I think the tire may be rubbing as well. What type of problem is this? I want to know what it is before I take it into a shop and feel like a idiot. Will I need a "tune-up", gear adjustment? tire something? The thunk is probably a loose fixed cup on your bottom bracket. The bb is the crank bearing, and the right side is the fixed cup. These sometimes come loose and cause that thunk, especially when you crank hard. The tire rubbing is most likely due to your wheel being out of true, and you'll just need to get it trued. If you go into the shop and tell them you think your fixed cup is loose and you need your wheel trued they'll think your a pro. We never get that, it's always, "I've got a thunk and I think something's rubbing, can you fix it?" you need to "true up" your back tire. meaning it was knocked off alignment and is not parallel with the other wheel Have a shop mechanic check the bottom bracket, mine did that and it turned out to be defective. i had it too, and then I found out that my pedal is broken The thunking may be your ball bearings coming/already loose. If the thunk happens when your pedal is coming down, then it's probably the ones located at the bottom of the frame by the crank. Go to a bike shop to get it checked out. While you're at it, get a tune up. It will only do you good, and should be done regularly or depending how much you use your bike. If the tire is rubbing, then your tire may be installed loosely, resulting in sideways movement. Either that or your brakes are not installed properly. As for the rattling, that may be caused by the chain grinding against the front derailleur if you sometimes forget to shift it when you're changing gears. Long-term grinding will wear down the chain faster, so try to avoid it. Before you take it to the shop, see if the thunk still happens when you shift to the largest chain ring. If it goes away, your large chain ring is bent inwards at the spot opposite your right crank arm (probably from hitting it against a curb), and it's pinching the chain against your second ring every time it passes over that spot. Take an adjustable wrench or some vice grips and bend it back into shape if you're confident enough. Edit: As for the rubbing tire, before getting the wheel trued, first check to see that the axle nuts properly tightened against the frame. Don't over-tighten it though, or your bearings will wear out prematurely. Happened to me a month ago. |
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