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Discussion Starter · #1 ·
In May I bought a Trek Fuel EX 9.9 and it has never properly shifted since I rode it out of the shop. I've gone to 6 different bike shops and no one can figure it out (hanger alignment perfect and the the derailleur has been properly set up using the red plastic SRAM b-adjustment tool - under sag). Not every time, but maybe on 6 out of 10 shifts up to the 42t or 50t sprockets, the chain rides on TOP of the sprocket teeth instead of meshing with them :


image2.jpg

image1 (1).jpg

I posted a thread about this on the Trek forums :

http://forums.mtbr.com/trek/2017-trek-fuel-ex-9-9-terrible-shifting-1051750.html#post13287214

Today the shop received a warranty cassette from SRAM but it still didn't solve the problem. so I bought a new chain and had an AHA moment when I installed it tonight.

The two largest sprockets have narrow wide type tooth profiles and the chain will not wrap around the sprockets on alternating teeth (just like on the chain ring) Narrow wide makes sense for a single chain ring but how can this possibly work on a cassette ? How can you guarantee the chain will be properly synchronized with the correct tooth profile so that narrow wide teeth are properly aligned with the alternating sized gaps of male and female chain links on EVERY shift ? And if this is supposed to work what else in my drive-train could be causing this ?

I'm not the only one experiencing this, the pinkbike Eagle review has the same problem - scroll down and look at the picture of the yeti - the chain is riding on top of the cassette teeth like mine.

https://www.pinkbike.com/news/sram-eagle-drivetrain-review-2016.html

This could also explain some other strange thing that's happening, once in a while, the chain gets out of sync with the lower derailleur pulley (it's also narrow wide) and the chain rides on top of the pulley teeth until I forcefully advance the pulley by one tooth (my mechanic started noticing this on his eagle bike too).

SRAM and all bikeshops so far have no explanation for what's happening.

Any ideas ??
 

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interesting post but if there was a design flaw rider complaints would be all over the place on the Internets yet it isn't

I'll install GX Eagle next week and will report back should I run into the same issue
 

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I have no issues with my X01 Eagle. I think your issue is you let lbs mechanics work on your bike.
 

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I have no issues with my X01 Eagle. I think your issue is you let lbs mechanics work on your bike.
+1 on the above...I've seen a few defective part problem reported, but by reading around I would recommend trying to self tune. Eagle seems to works on a higher precision level and not all mechanics know the system. Learn the details of the tuning by doing a self tune. I'm not a mechanic myself, but I installed and tune an XX1 eagle on a 2015 Stumpy. I had a few issues that I solved by resetting the low and high limit screws, but then no issues at all, other than some retuning with the barrel every 3 or 4 trips.

While reading your post my first thought was chain too as funnyjr suggested. Also take a look at the low limit screw and the make sure yourself that the b is well set.

From what I remember, eagle drivetrain only has a narrow/wide pattern on the chainring and on one of the RD pulleys. On the cassette you have some special cut tooth that help the chain on the up/down shifting process but not an actual narrow/wide on every one.

To help on understanding, take a look at this DIY
Take a look at this thread
 

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I've installed Eagle XO1 and XX1 on a few of my bikes without problems. Like others have said, check for binding. Also, check to make sure your shifter is pulling the cable smoothly (I saw a post about a defective Eagle shifter causing shifting problems somewhere on the interwebs).
 

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The 42 and 50 on the eagle are narrow wide. your chain is off by 1 tooth. It will sometimes skip on the 42 and 50 if the shift ramps don't line it up right. once it's in the correct place all is good. That skip can suck if you have the power down.
 

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The 42 and 50 on the eagle are narrow wide. your chain is off by 1 tooth.
I just unpacked the GX Eagle groupset and the two biggest cogs are indeed narrow wide! The chain doesn't fit on the cassette if it is "out of sync" and looks the same like the picture above!

I didn't install it yet but how's that supposed to work out? Do I have to make sure the chain is in sync every time I reinstall the rear wheel?
 

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I just unpacked the GX Eagle groupset and the two biggest cogs are indeed narrow wide! The chain doesn't fit on the cassette if it is "out of sync" and looks the same like the picture above!

I didn't install it yet but how's that supposed to work out? Do I have to make sure the chain is in sync every time I reinstall the rear wheel?
Really? that's a surprise...can you post a picture? are u sure is on the whole cog? I found this one on google and i don't see a clear wide-narrow pattern as in the chainring...
Cassette
sram-XX1-eagle-12speed-cassette-details02.jpg

Chainring
chainring.jpg
 

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i'll double check my x01 eagle cassette in a few hours. i dont remember them being narrow/wide design. 50t might have special teeth, maybe to assist in easier shifting, but not necessarily require special timing or alignment with the chain.

i haven't looked at the x01 eagle chain in awhile, but i dont remember it ever saying anything about aligning the chain or narrow/wide cassette. i watched a few youtube videos about eagle and none of the installers mention it either.

as far as i've seen/known/read, only the chainring and lower pulley have narrow/wide teeth profiles. the upper pulley is normal. i thought the cassette was normal too.

i thought the eagle cassette was just a standard 42-10t cassette with a 50t added on.
 

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All pictures show the cassette being equal width teeth, but they have different lengths (if length is the right way to describe it). Since chains have equal roller spacing, I wouldn't expect it to matter which tooth is in which gap in the chain, so I'm curious to hear about how this has happened to a few people.
 

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yeah im also curious how this is happening. i've been on x01 eagle for about 8 months so definitely not a pro, but i've swapped chains, removed, and installed chains multiple times on my bike and never had this issue.

would the b-tension screw have anything to do with this?

those with issues, have you checked your b-tension screw?
 

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I just unpacked the GX Eagle groupset and the two biggest cogs are indeed narrow wide! The chain doesn't fit on the cassette if it is "out of sync" and looks the same like the picture above!

I didn't install it yet but how's that supposed to work out? Do I have to make sure the chain is in sync every time I reinstall the rear wheel?
The shift ramps guide it onto the big cogs in sync. This happens 90% of the time. If it's out of sync it will jump 1 tooth and be in sync again. The N/W is for backpedal performance, so I doesn't jump off the 50/42.
 

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even with narrow wide profile the chain should jump cogs once aligned, worst case it skips a single tooth, it's really weird that it's jumping on top of the teeth, seems like the RD / shift are not setup correctlymaybe the rd is pushing the chain too much
 

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The shift ramps guide it onto the big cogs in sync. This happens 90% of the time. If it's out of sync it will jump 1 tooth and be in sync again. The N/W is for backpedal performance, so I doesn't jump off the 50/42.
that's some good background info you've got but if it works in 90% of the time does that mean at every 10th shift the chain will be out of sync?

I'll post pictures tomorrow before installation of the whole thing but the chain doesn't fit on the cassette if it's out of sync I wouldn't believe it myself if I hadn't seen it in hand
 

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that's some good background info you've got but if it works in 90% of the time does that mean at every 10th shift the chain will be out of sync?

I'll post pictures tomorrow before installation of the whole thing but the chain doesn't fit on the cassette if it's out of sync I wouldn't believe it myself if I hadn't seen it in hand
Unfortunately, yes it misses and jumps about every 10-20 shifts. I just soft pedal that shift and wait for a second to put the power down.
 

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Discussion Starter · #20 ·
The shift ramps guide it onto the big cogs in sync. This happens 90% of the time. If it's out of sync it will jump 1 tooth and be in sync again. The N/W is for backpedal performance, so I doesn't jump off the 50/42.
+1

This is exactly what's happening and probably explains why comments elsewhere describe a certain loudness or clunkiness when shifting into the lowest gears. SRAM confirmed to the shop that the chain can on occasion ride on top of the teeth but only on a bike stand. What I've noticed is that this happens also on the trail, the only difference is that when load is applied after shifting the chain skips and snaps/clanks while synching back into place. This is exacerbated when the b-screw isn't properly adjusted and why SRAM has a special tool to align it, but even when it is the problem can never truly be eliminated. Whether or not this is a design flaw can be debated, but it's certainly a compromised solution to prevent the chain from dropping when backpedaling.
 
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