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Discussion Starter · #1 ·
I just installed a new set of 180 XT cranks on my Trek 990. I was running a 34T ring on the inside position for proper alignment.

I must admit the best interface between ring and spider was on the outside position, but that comprimised the chainline.

I made it about 3 miles before I sheared 3 of the 4 chainring bolts in a dramatic failure. Most disappointing was the fact that I had bent the spider arms of my new crankset.

Is anyone running these cranks on their SS on the inside position? I have some good thoughts as how to strengthen the interface between the ring/crank, but wondered if anyone here has seen this problem?

Thanks-

bummed in MI
 

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err, 27.5+
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Must be the season for this kind of failure. Last night one of our riding buddies had a simillar mechanical. Basically the result of rushing to put new parts together and failing to properly torque the chainring bolts. He is out $40-50 for a new chainring.

Chainring bolts are very difficult to shear due to their large diameters. To shear off 3 they either worked a bit loose, were defective, or you have superhuman torque.

Best bet is to straighten the spider with a crescent wrench. Make sure to torque the chainring bolts down tight. Invest in some good quality Chainring bolts (steel may be best). Live and learn
 

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WAWE
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I'm betting your chainring was slightly crooked and wasn't fully pressed against all the spider arms.



Sidenote: There is an argument 5-arm spiders are more reliable. Should you lose a bolt on a 4-arm spider , only 50% of the ring is supported.. easier to bend/fold the ring. Loosening/losing chainring bolts isn't uncommon - check them regularly.
 

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-arschloch-
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wow

you must be superhuman put that much hurtin on those crankbolts. :p

I have been running a hollowtech II single ring up front for over a year. I'm on my second chainring, but no catastriphic failure yet...
 

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Discussion Starter · #5 ·
aosty said:
I'm betting your chainring was slightly crooked and wasn't fully pressed against all the spider arms.

Sidenote: There is an argument 5-arm spiders are more reliable. Should you lose a bolt on a 4-arm spider , only 50% of the ring is supported.. easier to bend/fold the ring. Loosening/losing chainring bolts isn't uncommon - check them regularly.
What is really the point to note in this issue is this:

aosty-while running the ring on the inside position there isn't really a lip on the spider side by which the ring is supported, only on the outside position. So in essense you have a point although the ring was straight, it's not designed to be run w/o the outer ring.

I have come up with a solution, but it's not a cut and dry issue with these cranks. Nothing money and lost riding time won't cure. Thanks for the input.
 

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Rollin' a fatty
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Not XT but ...

the same spider design, mine are Deore Hollowtech.



There's a small lip between both bolts that secures the middle ring but the big ring is the one that supports both of them. Under torque this will prolly fail if a bashring isn't there and that's the reason why I run my ring on the outside.

 

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Conundrum

cjpavlov said:
Is anyone running these cranks on their SS on the inside position? I have some good thoughts as how to strengthen the interface between the ring/crank, but wondered if anyone here has seen this problem?
I'm running the same set-up (XT Hollowtech II but w/Salsa 32t ring) in the middle position with zero problems.

It's possible the c/r bolts weren't fully tightened - or maybe they were just slightly over tightened to the point they were just about to strip out the threads. Were the c/r bolts aluminum or steel?
 
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