The stock chain rings on the cobbs are not the best.
Put some Praxis chain rings on them and you are good to go.

What do you mean by "wobble"?

"Chainring" wobble can come from a bunch of different places. The chainrings can be bent. The thickness of the chainring can be off/inconsistent at the mounting point. The mounting tabs on the spider can be bent, off, or of inconsistent thickness. The spindle (if it's a crank with a permanent spindle attached) can be off. If it's a crank without a permanent spindle attached or attached on the non-drive side, the spindle interface can be badly broached. All of these things will basically look like a wobbly chainring.
In none of these cases is the solution to hammer the chainring back into alignment. Especially with a new crankset.

How bad is the wobble? There is an "acceptable" margin of runout in the spec for every manufacturer, and with a new crank if it's far enough out JCOB should take care of you on this.

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The wobble is significant and changing gears in the big ring is worse than small ring.

Crankset was over 600 dollars. I hope this can be resolved. Seems like Shimano might not want to make smaller cranks because of these issues.

The length of the crank arm is completely irrelevant to this issue.

How much is "significant"? It's pretty easy to measure this...

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Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/

I don't think this will help your situation but I know Shimano makes a 160 in the R7000, I have one.

https://forum.slowtwitch.com/...p_P7349275/#p7349275

And your point is?

The (Cobb)chain rings suck , they flex.
Smaller cranks from shimano is not the chain rings it’s re- tooling to go shorter.
Shimano is not interested in short cranks for the tri fits , their money is oem .

I just remembered that you were asking about short cranks a few months ago.

BB / Crankset Installation error?
(if the installer recommends to 'hammer it back' into alignment).

If both wobble, and the larger one more, I'd first exclude that.
.

Does Praxis Chainrings work with the Cobb Carbon One Crankset? Since they are aluminum rings vs Carbon. I also noticed the flex on the chainring and didnt know if this was normal. Feel like I am being ghosted by JCobb since it has been 2 days of no response since I told them my problem and my LBS mechanic explanation. And the rep said they would review the issue with the team after I emailed them with photos.

Sorry for the novice question I am mechanically challenged

Thanks for remembering

"Does Praxis Chainrings work with the Cobb Carbon One Crankset? Since they are aluminum rings vs Carbon."


Are you saying that the chainrings on your Cobb crankset are made of carbon?

Oh! You've got a set of those!

There are no aftermarket chainrings (that I know of) available for those cranks. Fully proprietary one-piece chainring set.

You're going to have to go through the manufacturer to solve this.

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Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/

https://speedandcomfort.com/...of-carbon-one-cranks

That looks like they could wobble 'by design'.

I know who John Cobb is, but I am just shaking my head that he comes up with something like this.....

No the crankarms, Just unsure of compatibilty issues if I have to get different a new chainring.

Cobb makes 2 cranksets an alloy and a carbon. The alloy set has a different set up and uses 2 rings seperately

The carbon setup is fixed with both rings attatched.

Yes exactly they are. Any ideas on how to remedy. The bike shop doesnt want to work on it because they want to avoid liability and JCobb hasnt got back to me.

I'd give the manufacturer a bit more time to get back to you before attempting anything yourself. 2 days probably seems like a long time to you, but given the state of the bike industry right now It's really not in the "ghosting you" category, not by a long shot.

There simply won't be an easy do it yourself fix for this. By far your best bet is going to be a solution from the manufacturer.

FWIW, I'm with your bike shop. If I was your mechanic, I wouldn't work on this either. As you have described it, this is a warranty situation, not a repair situation.

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Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/

Thank you for your feedback. I should have realized changing cranks would be more of a challenge than it has been.

The chainrings on your crankset are proprietary.

You have a warranty issue.

Changing cranksets isn't a big deal.

The issue is quality control.

I received an email from Cobb today. Thankful, They are sending me a replacement. I dont know if its the whole set or just chainrings since proprietary for the carbon set.

If the chainrings are easy to bend and in fact this is causing the wobble is there a way to prevent it from happening again. Also should I put a new chain and new cassette on the replacement.

Thanks for the feedback

Odds are you just got a defective product. When chainrings bend, it doesn't usually result in a little bit of wobble, the outcome is either inexplicable throwing of the chain (because the ring bends, drops chain, bends back) or fairly catastrophic failure (because the ring bends and keeps right on bending).

What it seems like you've been describing is runout. Hopefully, the replacement they send you will be on spec and won't have it!

A long way back, Slowman wrote an article about just how darn hard it is to manufacture cranks well, based on his own experience doing so. I couldn't find it, but I'll ask him if he knows where/if it's still lurking on the site somewhere.

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Tech writer/support on this here site. FIST school instructor and certified bike fitter. Formerly at Diamondback Bikes, LeMond Fitness, FSA, TiCycles, etc.
Coaching and bike fit - http://source-e.net/ Cyclocross blog - https://crosssports.net/ BJJ instruction - https://ballardbjj.com/