Crank Asymmetry

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kentbrockman
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Joined: Fri Feb 08, 2008 11:37 pm
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by kentbrockman

So I've been rolling the new Specialized Tarmac for a few months. In that time I've been battling what I would call a fairly annoying imbalance between my left & right legs. After a fitting, I was under the impression that it was attributed to a leg length issue. Shims were added to my right cleat with no resolution.

I finally spent some time today and believe I have tracked it down to my S-Works cranks being offset ~7mm to the drive side. The cranks appear to be installed correctly, they just simply sit further to the drive side. To fully divulge, I am using an SRM which may contribute to the problem. I can accommodate this by using a shorter spindle on the right, but this feels like a hack.

My question is... has anyone else come across this issue? Is there a better fix than changing spindles?

deek
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Joined: Fri Aug 31, 2012 6:32 pm

by deek

How do you know that your cranks are offset?

by Weenie


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kentbrockman
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by kentbrockman

deek wrote:How do you know that your cranks are offset?


Measure from the center of the seatube to the outside of each crank arm. Also been feeling entirely unbalanced for months.

newforker
Posts: 128
Joined: Tue Feb 19, 2013 3:24 am

by newforker

I thought the same thing when I first got my S Works crank..this was while working at a Specialized dealer..took the calipers and measuring tape to every S bike that had a specialized crank..there was about 50 on the floor plus another 50 in the warehouse..they all were offset to the drive side...if you check on Specialized's website, under FAQ this is a question that pops up quite frequently..also make sure you tighten the 3x 1.5 mm allen bolts that pre load the crank, they can come loose pretty much everyride

kentbrockman
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by kentbrockman

newforker wrote:I thought the same thing when I first got my S Works crank..this was while working at a Specialized dealer..took the calipers and measuring tape to every S bike that had a specialized crank..there was about 50 on the floor plus another 50 in the warehouse..they all were offset to the drive side...if you check on Specialized's website, under FAQ this is a question that pops up quite frequently..also make sure you tighten the 3x 1.5 mm allen bolts that pre load the crank, they can come loose pretty much everyride


Wow, crazy. So the crank should be offset on the drive side?

deek
Posts: 406
Joined: Fri Aug 31, 2012 6:32 pm

by deek

kentbrockman wrote:
deek wrote:How do you know that your cranks are offset?


Measure from the center of the seatube to the outside of each crank arm. Also been feeling entirely unbalanced for months.

Just checking, a lot of people will measure to the chainstays which are definitely not symmetrical.

7mm sounds like a lot. I'm not too familiar with the Specialized cranks. Is there a spacer on the drive side? Can you have someone machine that down 3.5mm and then make up the difference on the NDS?

kentbrockman
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by kentbrockman

A'ight, I'm officially pointing the filter at Specialized. I've swapped out the SRM for the stock spider & still have a 5mm discrepancy on the DS. My wife has the same S-Works cranks (170mm rather than 172.5). Putting her cranks on my frame, low and behold I have symmetry between DS & NDS.

Knowing what the problem is gets me no closer to having it resolved...

TheKaiser
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by TheKaiser

kentbrockman wrote:A'ight, I'm officially pointing the filter at Specialized. I've swapped out the SRM for the stock spider & still have a 5mm discrepancy on the DS. My wife has the same S-Works cranks (170mm rather than 172.5). Putting her cranks on my frame, low and behold I have symmetry between DS & NDS.

Knowing what the problem is gets me no closer to having it resolved...


That is crazy, but troubleshooting like you are doing is great as it can turn up some crazy situations. On my MTB I once found that when turning my bars in one direction, the bar hit the top tube, whereas in the other direction, it did not. I thought that I had bent the stem in a crash, so I purchased another of the same brand, but aftermarket rather than OEM, and in a different color. I mounted it and found that I had the same issue. Tried new bars. same problem. There was some visible misalignment of the bar stem axis when viewed from the front, so sent the frame back to the manu to get checked out, and it was lost in transit. Got a new one covered by insurance, and built it up...problem still existed!

In the end, it turned out that the stem company had been welding all of their stems at a consistently crooked angle for some time. If I just bought a different brand from the beginning, I would have known, but hindsight is 20/20.

Anyway, someone earlier mentioned that this is a common issue in the Specialized FAQ. Anyone care to elaborate on what they have to say about it?

I have run into this on other brands back in the square taper days but it usually came down to either the crank company or bb company just not really caring about symmetry as one of their design priorities.

ghisallo2003
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by ghisallo2003

That is indeed crazy. One would assume that symmetry was part of the fundamental specification. I am exquisitely sensitive to rotation in the pelvis and this would have me in back spasm for weeks.

I think that this also highlights that fitting can be an expensive and fruitless process. Go and ask for your money back.

kentbrockman
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by kentbrockman

ghisallo2003 wrote:That is indeed crazy. One would assume that symmetry was part of the fundamental specification. I am exquisitely sensitive to rotation in the pelvis and this would have me in back spasm for weeks.

I think that this also highlights that fitting can be an expensive and fruitless process. Go and ask for your money back.


You are xactly right. I've never had a crankset be offset, so for months I've been changing saddles, pedals, even bars. I've wasted weeks & a shiz ton of money trying to track down why I felt so unbalanced.

I'm actually more than a little disappointed that Specialized would let something like this make it through the QA process. I'm sure my cranks are not the only ones with this problem.

Svetty
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by Svetty

I don't know much about Specialized/Tarmacs but are the cranks the same shape? If the chain stays aren't symmetrical the driveside crank may be spaced out further at the spindle but be straighter than the NDS one. The Q factor at the pedals will the same......
Just a thought :D

by Weenie


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kentbrockman
Posts: 33
Joined: Fri Feb 08, 2008 11:37 pm
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by kentbrockman

Svetty wrote:I don't know much about Specialized/Tarmacs but are the cranks the same shape? If the chain stays aren't symmetrical the driveside crank may be spaced out further at the spindle but be straighter than the NDS one. The Q factor at the pedals will the same......
Just a thought :D

Yeah, I was hoping the downtube & seattube were asymmetrical (the chainstays clearly are), but its simply a case of my cranks being shifted to the DS. By swapping my cranks with my wife's (identical S-Works only 170mm), everything is back in alignment.

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