[millerlynx]

Wondering if anyone can help me figure out the source of a loud sound my bike is making. Here are the details:

The bike is a brand new all carbon Turner Czar. 1st 3 rides, it was perfect, since then it makes a loud knocking sound occasionally. It occurs almost always (95% of the time) when pedaling. However, every once in awhile it will happen right after I stop pedaling. It only occurs when the drivetrain is under pressure -- so when climbing (except on those odd times when it happens right after I stop pedaling). It never occurs when I'm pedaling on an easy flat or down hill. It also never occurs when coasting. It happens whether I'm in the saddle or out, although primarily when in (perhaps because I generally climb in the saddle). And it is occasional -- not every crank or revolution, but over the course of a ride I'll hear it a hundred times. It can/does happen in any/every gear.

Because it never happens when going down hill or coasting, I'm pretty certain it is not the frame (which I've inspected several times for cracks, but can't find anything), wheels, or brakes. It also seems unlikely that it's the shocks.

It seems to be associated with the drive train and it seems to be coming from right below me, rather than from the rear hub/cassette. So my best guess is the bottom bracket or the cranks, but the fact that it does happen AFTER I stop pedaling occasionally befuddles me.

I also thought about the seat/seatpost, but the fact that it happens while out of the saddle climbing, but never in the saddle when on flats or downhills would seem to rule that out.

Because it really only occurs when the drive train is under pressure, I can't replicate it in a workstand, so I can't more closely pinpoint where it is coming from.

Drivetrain is SRAM 1x11. Shocks/Fork are Fox (RP23 and Float 29 CTD).

Anyone have any ideas? Any further info needed or questions?

Thanks -- Chris.

 

[Haint]

There may be a problem with the Shock - an overly-high static Compression damping. Or a shim may have bent on the Compression shim arrangement. The shock should be naturally tuned with the particular suspension, and the shock should allow full range of any adjusting dials.

Just run the compression dial up and cycle the rear suspension by the seatpost. If the noise is present and becomes louder - that's what it is.

 

[time229er]

I would be taking a hard look at the BB...it certainly could be the source...of course their website says it's a PF...who-da-thunk-it :madman: personally, I will stick to the proven poop :thumbsup: if I have the option...and yeah I am aware it is heavier but it just works

 

[Hang 21]

A couple years ago, my then brand new Tallboy C had similar symptoms develop after the first or second time I rode it. It was a sharp popping sound akin to what might be expected if the frame were struck with a wooden dowel rod. It only occurred when the cranks were under load and seemed to have no correlation to suspension movement, so my initial thought was a drivetrain issue. Turned out that the suspension pivot axles and wedge washers didn't have enough grease on them. After regreasing, everything was happy.

 

[derekbob]

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