Rumbling through cranks when in highest gear
I've noticed a rumbling through the bike when using the turbo trainer in higher gears/efforts.
I originally thought it was the turbo tyre wearing out after 2 years of heavy use, but that didn't solve it.
Today, I've isolated it down to the drive train, and can really feel it through the pedals when in 50/11 (top). I've checked there is no rubbing anywhere, and the derailleurs all seem to be setup spot on.
I then thought it might be down to the fact I use AbsoluteBlack oval chainrings, so swapped these back over for the stock 105 but the same issue there.
What I have noticed is a slight gap between the frame and the bottom bracket, which I am not sure has always been there or not.
Is this normal:
I originally thought it was the turbo tyre wearing out after 2 years of heavy use, but that didn't solve it.
Today, I've isolated it down to the drive train, and can really feel it through the pedals when in 50/11 (top). I've checked there is no rubbing anywhere, and the derailleurs all seem to be setup spot on.
I then thought it might be down to the fact I use AbsoluteBlack oval chainrings, so swapped these back over for the stock 105 but the same issue there.
What I have noticed is a slight gap between the frame and the bottom bracket, which I am not sure has always been there or not.
Is this normal:
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Comments
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worn BB? worn freehub/wheel bearings? take your pick something worn.http://www.thecycleclinic.co.uk -wheel building and other stuff.0
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I too notice a rumbling through the cranks when on the turbo in the 50 ring and some smaller cogs. Seems ok in the small ring and most rear cogs. Never notice it out on roads as they are so rough now all I hear is my skeleton rattling. Everything else is fine and tight.
Sometimes. Maybe. Possibly.
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That gap shouldn't be there and the dust cap over the bearings looks wonky although that could be the angle of your pictureRule #5 // Harden The Feck Up.
Rule #9 // If you are out riding in bad weather, it means you are a badass. Period.
Rule #12 // The correct number of bikes to own is n+1.
Rule #42 // A bike race shall never be preceded with a swim and/or followed by a run.0 -
You're probably feeling the chordal effect. A chain can only bend where two links join, so as the cog rotates, the chain will rise and fall slightly depending on whether a cog tooth or the valley between two cog teeth is perpendicular to the path of the chain, and this changes the velocity of the chain slightly and leads to the roughness you've observed. The smaller the number of teeth on the cog, the greater the angle between two adjacent teeth on the cog, and the greater this effect. The graph below shows the percentage variation in chain speed plotted against the number of teeth. You see see that a 20t cog only has about 1% variation, which really can't be felt, whereas an 11t cog has a bit over 3% variation, and that can definitely be felt.
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