Changing crankset

kilroy
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Changing crankset

Postby kilroy » Wed May 29, 2024 8:32 am

Hi guys. I've been looking at potentially shortening my cranks from 172.5mm to 170's. My bike is fitted with 11spd Ultegra cranks (R8000 series) and a BBR60 (BSA) bottom bracket.

I've seen some nice S-Works and SRAM carbon cranks for reasonable money. Some of them mention being compatible with a BB30 bottom bracket. I take it I would need to change the BB as well? I'm assuming my bike would accept a BB30 if required?
Any pointers would be appreciated.
2020 Specialized Roubaix Comp Di2; 2021 Trek Powerfly 5.

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jaseyjase
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Re: Changing crankset

Postby jaseyjase » Wed May 29, 2024 10:03 am

If you're bike currently is running a BSA bb, then you most likely cant run a BB30 bb.

However SRAM make BSA compatible cranks, so you just need to purchase that and the matching BSA bb to suit.

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P!N20
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Re: Changing crankset

Postby P!N20 » Wed May 29, 2024 11:03 am

I'll be amazed if you notice any difference between 172.5 and 170.

Nobody
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Re: Changing crankset

Postby Nobody » Wed May 29, 2024 12:11 pm

P!N20 wrote:
Wed May 29, 2024 11:03 am
I'll be amazed if you notice any difference between 172.5 and 170.

Yeah, 165 is you want to notice a change IMO. I went from 175 to 165 a decade ago. Yes, I noticed the difference.

kilroy
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Re: Changing crankset

Postby kilroy » Wed May 29, 2024 1:51 pm

Fair enough, thanks for that. I do remember reading about 165mm cranks being the sweet spot for high cadence climbing but to be honest didn’t really want to make such an extreme change to crank length as I’ve had knee and back issues in the past. It would make sense to pick a compatible crank rather than replacing the BB so I’ll keep that in mind.
2020 Specialized Roubaix Comp Di2; 2021 Trek Powerfly 5.

Nobody
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Re: Changing crankset

Postby Nobody » Wed May 29, 2024 2:21 pm

kilroy wrote:
Wed May 29, 2024 1:51 pm
...but to be honest didn’t really want to make such an extreme change to crank length as I’ve had knee and back issues in the past.

The point of short cranks is often to help people who have knee, hip, or other issues that can be related to bike fit (body mechanics) or inflammation issues. Knee problems was the major reason I changed. It marginally helped. One piece of the puzzle.

Mr Purple
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Re: Changing crankset

Postby Mr Purple » Wed May 29, 2024 5:21 pm

You won't notice a change from 172.5mm to 170. I started on 170, went to 172.5 and back to 170. No difference.

I have heard of someone making a mistake and accidentally running a 170mm on one side and a 172.5mm on the other. Apparently he noticed no difference either.

kilroy
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Location: Riverina, NSW

Re: Changing crankset

Postby kilroy » Thu May 30, 2024 10:41 am

Mr Purple wrote:
Wed May 29, 2024 5:21 pm
You won't notice a change from 172.5mm to 170. I started on 170, went to 172.5 and back to 170. No difference.

I have heard of someone making a mistake and accidentally running a 170mm on one side and a 172.5mm on the other. Apparently he noticed no difference either.
Wow, I think my body would notice after a couple of hours!
2020 Specialized Roubaix Comp Di2; 2021 Trek Powerfly 5.

kilroy
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Location: Riverina, NSW

Re: Changing crankset

Postby kilroy » Thu May 30, 2024 10:44 am

Nobody wrote:
Wed May 29, 2024 2:21 pm
kilroy wrote:
Wed May 29, 2024 1:51 pm
...but to be honest didn’t really want to make such an extreme change to crank length as I’ve had knee and back issues in the past.

The point of short cranks is often to help people who have knee, hip, or other issues that can be related to bike fit (body mechanics) or inflammation issues. Knee problems was the major reason I changed. It marginally helped. One piece of the puzzle.
Sweet, might have to look into the 165’s. I kinda wish I still had my Assimo power meter pedals as my 4iiii power meter will be a bit too long!
2020 Specialized Roubaix Comp Di2; 2021 Trek Powerfly 5.

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Duck!
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Re: Changing crankset

Postby Duck! » Sat Jun 01, 2024 3:16 pm

jaseyjase wrote:
Wed May 29, 2024 10:03 am
If your bike currently is running a BSA bb, then you most likely cant run a BB30 bb.

However SRAM make BSA compatible cranks, so you just need to purchase that and the matching BSA bb to suit.
No ifs, buts or maybes, a BB30 crank cannot be fitted in a BSA frame. BB30 uses the same 68mm shell width, with a larger bore to allow internal fitting of the bearings; the crank spindle is only long enough to fit through the internally-mounted bearings.

BB386 format cranks can be an option though. They use the same 30mm diameter spindle as BB30, but the spindle is longer in order to fit through 86mm press-fit shells, and also BSA shells with suitably larger outboard bearings.

SRAM's "DUB" crank & BB set is similar to BB386 in that it can be adapted to fit most frame formats, however it uses a pointlessly unique spindle diameter that requires a compatible bottom bracket.
I had a thought, but it got run over as it crossed my mind.

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WyvernRH
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Re: Changing crankset

Postby WyvernRH » Sun Jun 02, 2024 12:55 pm

Duck! wrote:
Sat Jun 01, 2024 3:16 pm
jaseyjase wrote:
Wed May 29, 2024 10:03 am
If your bike currently is running a BSA bb, then you most likely cant run a BB30 bb.

However SRAM make BSA compatible cranks, so you just need to purchase that and the matching BSA bb to suit.
No ifs, buts or maybes, a BB30 crank cannot be fitted in a BSA frame. BB30 uses the same 68mm shell width, with a larger bore to allow internal fitting of the bearings; the crank spindle is only long enough to fit through the internally-mounted bearings.

BB386 format cranks can be an option though. They use the same 30mm diameter spindle as BB30, but the spindle is longer in order to fit through 86mm press-fit shells, and also BSA shells with suitably larger outboard bearings.

SRAM's "DUB" crank & BB set is similar to BB386 in that it can be adapted to fit most frame formats, however it uses a pointlessly unique spindle diameter that requires a compatible bottom bracket.
Interesting... I must admit I have difficulty (ie no real interest) in following all the BB bracket variations but I do have a BB386 bottom bracket on my FELT gravel bike and I bought the chainset shown below which has 'BB30' written on it to convert it to a triple, being assured it would fit by the shop (sucker...). As Duck mentions, this didn't work as the axle was not long enough to prevent the inner ring fouling the large BB386 bottom bracket.
So to the point.. I repurposed this chainset for my early 90's TREK road bike which has a standard (BSA) bottom bracket using an outboard bearing kit made by <Edit -Rotor IIRC-Edit.> Sorry, checked the box, it was a conversion kit by FSA.

Image
Image

As you can see it worked fine, apart from requiring some creative thinking to get the front derailleur outboard a little further.
So, was I just lucky or are these really BB386 cranks?

Personally, I've taken an oath never to buy another bike that does NOT have a standard bottom bracket shell.... :P

Richard

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