BB386 crank in BB30 frame - Chainline?
01-28-18, 10:02 PM
#1
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BB386 crank in BB30 frame - Chainline?
There are spacer adapters from the crankset manufacturers to fit the BB386 cranks in BB30/PF30 frames, but won't the chainline be severely off since the BB386 spindle is 18.5mm longer than a BB30 spindle?
01-28-18, 10:07 PM
#2
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The 18.5mm of extra spindle will be taken up by spacers on both sides of the BB, making the BB30 effectively as wide as BB386.
If you just stuck a BB30 crank on an extra long spindle the chainline would be off, but the two cranks are designed differently. And the differences are why BB386 cranks have wider Q and less ankle clearance.
01-28-18, 10:12 PM
#3
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No. The BB386 is designed to have a long spindle, so it will have the same chainline as every other road crank.
The 18.5mm of extra spindle will be taken up by spacers on both sides of the BB, making the BB30 effectively as wide as BB386.
If you just stuck a BB30 crank on an extra long spindle the chainline would be off, but the two cranks are designed differently. And the differences are why BB386 cranks have wider Q and less ankle clearance.
The 18.5mm of extra spindle will be taken up by spacers on both sides of the BB, making the BB30 effectively as wide as BB386.
If you just stuck a BB30 crank on an extra long spindle the chainline would be off, but the two cranks are designed differently. And the differences are why BB386 cranks have wider Q and less ankle clearance.
01-28-18, 10:23 PM
#4
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Maybe this is just eluding me but I don't see how using the BB386 crank in a BB30 frame with the spacers won't put the rings outboard of the correct chainline by 9.25mm.
Left is BB386, right is BB30
Left is BB386, right is BB30
01-28-18, 10:29 PM
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And that longer spindle with the same chainline is why the left crank sticks out further on the outside.
01-28-18, 10:36 PM
#6
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And if you look on the right you'll note that the spindle ends short of the small chainring with a flared black area, while on the left it extends under the small ring. That's a difference of (86-68/2=) 9mm. And the other side will also be 9mm shorter.
And that longer spindle with the same chainline is why the left crank sticks out further on the outside.
And that longer spindle with the same chainline is why the left crank sticks out further on the outside.
Maybe I'm totally missing and will see it in the morning.
The two have almost the same q-factor, which is probably why the crank arm profiles look different.
The pic is from here:
https://www.bikerumor.com/2011/12/22...rison-weights/
My interest in this is from wanting to use a crankset that only comes in BB386, in my BB30 frame.
Last edited by vinuneuro; 01-28-18 at 10:40 PM.
01-28-18, 10:56 PM
#7
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The picture has the rings aligned, but you have to look at it from the perspective of the centerline of the frame. So if the spindle ends were lined up, the rings on the left in the first pic would be higher than the rings on the right. No?
01-28-18, 11:51 PM
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Bare with me. I see that, but it doesn't account for the spindle length difference. If it did, the bottom of the spindle's in the pic would be at the same position. Below the unpolished section you can clearly see that the spindle extends much lower.
Maybe I'm totally missing and will see it in the morning.
The two have almost the same q-factor, which is probably why the crank arm profiles look different.
The pic is from here:
https://www.bikerumor.com/2011/12/22...rison-weights/
My interest in this is from wanting to use a crankset that only comes in BB386, in my BB30 frame.
Maybe I'm totally missing and will see it in the morning.
The two have almost the same q-factor, which is probably why the crank arm profiles look different.
The pic is from here:
https://www.bikerumor.com/2011/12/22...rison-weights/
My interest in this is from wanting to use a crankset that only comes in BB386, in my BB30 frame.
01-29-18, 11:45 AM
#9
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Thread Starter
That looks pretty much like an 18.5mm difference in length, with 9mm of that being on the drive side filling the difference between the narrower 68mm BB shell and where the chainrings are located. If you take the BB386 crank and stack 9mm of spacers on the drive side you end up with the same offset that the BB30 crank is built with.
