# 7900 cranks out of spec?



## tyro (May 15, 2005)

I have a set of 7900 cranks with a q-factor of 150mm. They are supposed to be 147mm. Is this out of spec enough that Shimano would/should replace them?


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## ukbloke (Sep 1, 2007)

I can't imagine that this would vary by 3mm from 7900 crankset to 7900 crankset ... i.e. I think all 7900 cranksets would be the same, so a replacement is unlikely to fix the problem. Are you sure that the cranks are fitting snugly to the BB (no lateral play)? The other possibility is that Shimano didn't publish the increased Q factor measurement for 7900. It does seem that Q factor has been gradually widened with each generation.


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## ukbloke (Sep 1, 2007)

It is not clear to me that Shimano publishes Q-factor numbers. If you google search the one that pops up is from a recent story by Nick Legan at velonews and that seems to be the source of the 147mm number. Another result I see is your post at another forum! Unless you can find a Shimano publication of this number, I don't think you have any grounds to return them based on being out of spec.


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## tyro (May 15, 2005)

ukbloke said:


> It is not clear to me that Shimano publishes Q-factor numbers. If you google search the one that data that pops up is from a recent story by Nick Legan at velonews and that seems to be the source of the 147mm number. Another result I see is your post at another forum! Unless you can find a Shimano publication of this number, I don't think you have any grounds to return them based on being out of spec.


This is the only Shimano-specific forum I know of, so I posted here.

I am sure that the crank is snug to the bb. There is no play. I saw the Velo News article too. The SRAM q-factor are off too. Advertised as 145 mm when in reality they are 150 mm.

Shimano says that the Q-factor "remains unchanged" from the last generation. The last generation is 7800 and my 7800 cranks measure 147 mm. 147 mm to 150 mm seems like a change to me.

I wouldn't care at all except for the fact that they trash my knee.


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## ukbloke (Sep 1, 2007)

tyro said:


> I wouldn't care at all except for the fact that they trash my knee.


Well that sucks, sorry to hear about that. If you are this sensitive to it, and cannot adjust by cleat position, maybe you should stay with the 7800 cranks? Or maybe you need a professional fit to confirm this, or to see whether something else in your bike fit or physical conditioning has changed?


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