hch389

1. Chain catching
Problem:
(tried to insert youtube video of it, but forums rules wont leet me until I have 10 posts)
The chain is catching on the chainring teeth. There are 2 specific teeth that do this, so even if chain shifts 1 link on the chainring, it will always be catching one of these 2 teeth.

Scenario/method:
It happens on my big-small gear ratio (48-11).
If looking from above, I can see it is catching on the narrow chain link on the inside. If I shift to 48-13, then it goes away.

Specs:
2015 Specialized Diverge Comp Smartweld (originally Praxis Turn Zayante 50/34)
New Praxis Zayante crankset (48/32)
I measured the big chainring chainline to be 49mm, so moving it further out isn't really a good idea since 49mm is already wide for my bike.
The rear hub is 135mm, 11 speed.
Stock Praxis M30 bottom bracket that came with the bike


2. Cranks off center
Problems: drive-side crank is 4mm further from the bike centerline compared to NDS crank.

Scenario/method:
I measured the face of the crank/pedal to the center of the seat tube. DS is 4mm further out.
Measured older cranks, and it is within 1mm. I used calipers, and bike shop also measured with a tape measure and agreed there was a 4 mm difference.

Specs:
Bought the new dust cover set from Praxis and used the width's they had in the instructions
BB30 M30 bottom bracket, Direct Mount chainset, so I used a 1mm cover and wave washer on the DS.
The old crankset has an integrated spider, DS had 2mm cover and no wave washer.


I emailed and called Praxis and they said my bike probably has 142mm rear dropouts, and either way, a bit of catching is normal and will go away after wearing down.

They also said they don't know why the cranks aren't center. They said since I installed it myself, a bike shop should check it and then call Praxis again if it is actually an issue. I am 99% sure I installed it as instructed.


I upgraded because I wanted a power meter and ability to run sub-compact chainrings, so I bought the cranks from Praxis directly for $530 (crankset+powermeter) + $10(dust cover)
I emailed Praxis to make sure it would work with me 2015 model bike that has an older crankset and BB. They said it would.
Thus, I expected that, for $540 and their confirmation, it should work!

The chain catching a bit seems okay to me, but still a bit annoyed since these are brand new cranks and if they costs hundreds of dollars, I expect it to work well out of the box.

Being off center is a big issue imo. My only guesses are 1. the older BB is actually different from the newer one and Praxis representative are misinformed, 2. cranks are just offset by design????

If this turns out to be a big hassle, I'm quite disappointed. I would've just stuck with my older cranks, and got 4iiii power meters installed on them (and accept the ~ 2 week wait time). And not spent all the extra money and time.

Any ideas or suggestions?
(And yes I know, 4mm might not be a lot and might not be felt, but will be a PITA to compensate for if it actually becomes an issue. Plus, I'm pretty sure basically every other system wouldn't have this issue, and I wouldn't have bought this if I had known.)

Sorry if this sounds like a rant. But I actually want to fix this asap to get out there to ride, now that I've dropped the money for a power meter!

Andrew R Stewart 

Crank arms have been asymmetrically spaced from the frame's centerline for decades. generally this is more of a body alignment thing if really bad but NOT directly an indicator of chain line alignment. Chain line involves the rings, not the arms.

Have you measured the actual chain line (not a published dimension one)? I suspect the chain link catch is likely at points on the large ring where the teeth are shaped for shifting ease, or the shift gate as it's sometimes called. If the catch is slight then it will dimension a bit with wear in. Does the catch cause the chain to jump up or is it just noise/feel that you sense?

It's really hard for a third party to anticipate every type of combo (frame, rear end, BB) their crank might be paired with. So a small deviation from that "perfect world" we dream of is common. Usually this offness is small enough to not be a real issue. I suppose you could try different rings on the same crank arm to see if a different tooth/shift gate shaping is better.

BTW this issue would be a big no deal for some of us as we would only use the 48/11 combo when hammering down hill. At 90 rpm you will be going over 31mph. Not many will be able to do this on the flats for very long Andy

Sapperc

I have the Praxis Zayante crankset on my 2016 Specialized Roubaix. The older Specialized bikes use their proprietary OSBB spec. Praxis has a spec and instructions that specifically address the Specialized OSBB. Be sure to follow them.

Does the crank rotate true as viewed from above or below? If not something is wrong. If the crankset is snug in the bottom bracket, check the chainring bolts. Did you service and reseat the bottom bracket bearings? Perhaps recheck them. Is the chain catching on the inner most surface or outer most surface of the narrow links? If it’s to the inside less (narrower) washers on the drive side should bring it back inline. If it’s to the outside, try the original 2mm drive side washer to bring it back inline perhaps. But in any event be sure to follow the Praxis installation instructions. They should be right on target. My suggestions are only meant as things to look for in the installation guide. I found the guide to be a little terse and difficult to follow without close attention and multiple readings to insure I understood my first time through.

No, even brand new, especially brand new, the chairing teeth should not catch and stumble during shifting. Shifting should be sharp and crisp if everything is aligned properly including the front derailleur which would need realignment and adjustment to accommodate the new chainrings. Chainring teeth will not always be centered within the links as some teeth are angled as shift gates as noted above. But that assists - not interferes with shifting.

Don’t know why the tech at Praxis couldn’t answer your questions. They were helpful and knowledgeable when I’ve called in the past. Call back and ask for a senior tech or tech supervisor.

Unless the new crankset is out of spec, this should be fixable with correct installation. Best of luck!

AnkleWork

Don't borrow trouble; this is not a mechanical problem with your bike.

Getting out to ride IS the fix.

hch389

To answer some of the questions:

Chainline:

Big chainrig: 49mm is measured. Small chainring is 43mm. So chainline ~46mm.

Published # is 43.5mm by Praxis. So it is actually already further out for some reason, but still catching. Basically on the big chainring, it is cross chaining the opposite from normal direction.


It hangs up before falling onto the chainring.

I just made my video public so that it is searchable:

Youtube: "New Praxis Zayante Chainrings Catching on Bike Chain"

Also, for the off-center measurements, youtube: "New Praxis Zayante Crankset Offset"


Yes, I definitely don't think it's a massive issue since it's only 48-11 haha. But, this should be a very normal setup. 135mm rear spacing, 2015 Specialized Diverge with 'not out of the normal' chainstay length.

I did a gravel ride with my hybrid 1x gearing, biggest gear was 30-11 and spun out so badly. Was told the average pace was 16-17mph.... No idea that meant 25mph average for gradual decline/tailwind sections and continually smashing even at 30mph, ended up doing 17.5mph for 35 miles. With this gravel bike and my old 50/34, it was way better, and the group did 18.5mph for 36miles (longer detour). I'd definitely use 48-11 at times.


Are there sources you can link me to regarding asymmetric cranks/pedal spacing from manufacturers and other websites?

I just read another forum thread about it, and there was a lot of heated debate whether it mattered or not

If Praxis says to me, officially, that it is supposed to be that way, then I'd accept it, inform them I wish they would have the info more easily available to buyers. I'd also hope to know why they changed it from 1mm to 4mm between their older and newer cranks. However, since the Praxis tech said he didn't know, that is an issue.

I will call again next week. The Praxis tech said he was the only one available this week as everyone's on vacation. I brought it into my LBS. Next day, they said my BB and everything was installed perfectly. But they measured it to be centered within 1 mm. I asked to see how they checked, and they showed me. However, they measured it to the inside of the crank arm, and the cranks aren't equal thicknesses. Then they measured again from the outside of the crank arm, and it showed about 3-4mm difference. They just said it's pretty close. However, if it's designed to be centered, then 4mm is a lot.


I took it for a 17 mile ride, and my right foot actually was very uncomfortable, and I had to move my cleats such that my foot was FURTHER out. It seemed to help but my foot still hurts with these new shoes and crankset. So, maybe the fact that the DS is 4mm further out might turn out to be helpful for me...


I've had knee pain in the past where I used shims and washers to try to help. So, a few mm might actually make a difference..

shelbyfv

Hopefully the GRX will soon be available

redlude97

Just file the inside of the tooth, you won't even notice it

TiHabanero

I use as narrow a Q factor as possible, and every 39/53 set up I have does this very same thing. I just let it rub as it doesn't bother me. Let it go, let it goooo!