# Crank arm compatibility?



## kbwh (May 28, 2010)

Q: When Campag went from 5 to 4 arm UT crank sets, did they make any changes to the axle and Hirth joint?










Asking because I'm contemplating a Stages Campagnolo power meter, and my UT cranks are 2009.


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## nova_rider (Sep 23, 2005)

kbwh said:


> Q: When Campag went from 5 to 4 arm UT crank sets, did they make any changes to the axle and Hirth joint?
> 
> 
> 
> ...


Should not be an issue.

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## spade2you (May 12, 2009)

Are these going to be compatible with the Bora TT cranksets? Been wanting something attractive and a 55/44t for my TT bike.


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## kbwh (May 28, 2010)

If nova_rider is correct, i.e. that the mechanics of UT are unchanged since initial release, it should fit just fine. The Bora UT crank is SR with Ti axle, isn't it?


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## nova_rider (Sep 23, 2005)

It may look a bit odd as Bora Ultra crank arms look very different from SR arms. If you don't mind having mismatched arms, I don't see why it wouldn't work with SR version, as long you don't need anything above 175mm.


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## spade2you (May 12, 2009)

nova_rider said:


> It may look a bit odd as Bora Ultra crank arms look very different from SR arms. If you don't mind having mismatched arms, I don't see why it wouldn't work with SR version, as long you don't need anything above 175mm.


Understood on not matching. I think Vision also makes a similar crankset. I think Stages had a matching crankset that was posted to USA Cycling members as part of a discount. When I asked them, they said the exact match was not available, but they had something that would work. 

I'm a shorty with 170mm cranks arms. I could maybe see myself getting one of these if I can push enough watts to justify the bigger chainrings.


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## kbwh (May 28, 2010)

I asked Campag:


> Hello, Is a left side current Ultra Torque crank arm (steel axle) mechanically compatible with a 2014 or older (5 bolt) right side Ultra Torque steel axle crank? I'm asking because I'd very much like to put the just released Stages power meter on my bike which has a 2009 Ultra Torque Super Record crankset with steel axle. Thanks.


Campag answered thus:


> Thank you for consulting us.
> 
> Unfortunately, no way to proceed the way you suggested. Not compatible components. Current 2017 and 2016 Ultra Torque cranks must be paired each other with same year ranges’ products.
> 
> Apologies,


Next bike then.


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## 1Butcher (Mar 15, 2011)

If I was a large company, I would stick to that statement. 

If you say it will work, you're stuck with that statement and all the liability baggage it comes with. If you say it does not, you are in a much safer position when something goes wrong.

So, I would suspect that you will have to ask the peanut gallery to get a good answer. So far, I would agree with the others. If Campagnolo does not want it to work, I would suspect they would design it not to work [like left hand threads on the SR ti cranks]. I believe it would work just fine.


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## nova_rider (Sep 23, 2005)

While Campy might use "incompatible" as their official response, there are other factors that may be good reasons not to mix the two, even if they dimensionally match. First, stainless steel and titanium have different material properties that will impact the torsional rigidity. Since measuring torsional deflection is how most power meters work, mixing the two may cause inaccurate values. Second, there may be galvanic corrosion issues between these two dissimilar metals in contact. SS and Ti are relatively inert, but when combined with moisture and salt from rain, drinks, sweats, etc. It may result in corrosion issues on rather expensive components AND at a rather critical junction. This is probably also why SR crank uses Ti bolt instead of steel, and not just to save an extra 0.83 grams... Something to think about.


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## kbwh (May 28, 2010)

It was, as written in my opening post and to Campag, never my intention to mix Ti and steel axles. Also steel axle cranks use a rechts tread bolt whereas Ti uses links. 

I am well aware of what galvanic corrosion can do, also to Ti.

I'd like to see the construction drawings and material specs for a 2009 steel UT axle and a 2016-17, though.


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## 1Butcher (Mar 15, 2011)

I agree Novarider, but reversing the treads to make certain you could not swap them is something they did not have to do. So, I believe if they wanted the arms from the new to old not to work, they would have done that. I would certain to keep costs down and the assembly line going, there is no difference.


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## nova_rider (Sep 23, 2005)

1Butcher said:


> I agree Novarider, but reversing the treads to make certain you could not swap them is something they did not have to do. So, I believe if they wanted the arms from the new to old not to work, they would have done that. I would certain to keep costs down and the assembly line going, there is no difference.


The right side of UT is just a thru hole, so thread direction shouldn't​ matter. I suspect this is done due to the weaker Ti fastener.


nova_rider said:


> While Campy might use "incompatible" as their official response, there are other factors that may be good reasons not to mix the two, even if they dimensionally match. First, stainless steel and titanium have different material properties that will impact the torsional rigidity. Since measuring torsional deflection is how most power meters work, mixing the two may cause inaccurate values. Second, there may be galvanic corrosion issues between these two dissimilar metals in contact. SS and Ti are relatively inert, but when combined with moisture and salt from rain, drinks, sweats, etc. It may result in corrosion issues on rather expensive components AND at a rather critical junction. This is probably also why SR crank uses Ti bolt instead of steel, and not just to save an extra 0.83 grams... Something to think about.



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