Inner chainring to chainstay clearance

[kw]

Hi,

I just completed building my new Sam Hillborne (my first time building myself!). However, the inner chainring is very close to the chainstay and I’m wondering what is the minimum clearance that’s thought to be safe? Riv said the installed BB is 113mm. I wondering if I should get a 115mm or 118mm BB? I’m running a Spa Cycles RD2 crank 44/28 double to 9 speed cassette. Thanks for the help!

-Ken

[Scott Garrison]

I have a very similar setup on my Hillborne with a Spa Cycle TD-2 crank with 44/28 chainrings going to a 9 speed cassette. I replaced the 110mm bottom bracket that came with my Hillborne with a 115mm. Mine is also close, but so far no issues and it has a good chainline. You may want to replace it for peace of mind, but if you aren't rubbing, you're probably fine.  

[Danny]

I have a bike or two with that much clearance for my inner ring, and have never had an issue, YMMV of course. 

How much chainstay clearance do you have on the NDS crank arm? If you've got some wiggle room on the NDS, you could add a spacer to the bottom bracket on the driveside to give you a couple mm more clearance.

Danny

Madison, WI

[Patrick Moore]

That gap looks fine to me; I expect you won’t be flexing the ring or frame a great deal in the Low Lowish combinations. FWIW, I’ve ridden similar gaps on several bikes with no problem.

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Patrick Moore

Alburquerque, Nuevo Mexico, Etats Unis d'Amerique, Orbis Terrarum

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[Kenneth Wiss]

Thanks everyone!

@Scott- Thanks for sharing your experience.

@Danny - The NDS crank arm has plenty of clearance, thanks for idea to add spacers. This is all a bit new to me, I've never done my BB or crank installation before. Is there any downside to using spacers instead of a longer BB? I'm assuming my NDS crank arm would be pushed out further but beyond that?

@Patrick - Good point that I'll really only be in that ring for Low Lowish gears. I guess I still worry the frame flex will hit the chainring teeth regardless of the gears I'm in. 

All said, sounds like even just 2mm more clearance will be enough and will give me peace of mind too!

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[Dave Johnston]

I would add a 1mm spacer to the drive side. The spacer is the same as a cassette spacer.

[Danny]

Ken, adding a spacer on the driveside will bring the NDS crank arm closer to the chainstay and push the DS crank arm (and chainrings) farther out. I think the spacer is just a simpler and less expensive solution than sourcing a new BB since you have wiggle room with chainstay clearance on the NDS.

(BB spindles aren't always symmetrical, so if you did go with a 115 or 118, you'd want to make sure those extra millimeters are being added to the right side of the spindle.)

And as Dave mentioned, cassette spacers are the same diameter that you'd need for a BB spacer, so should be easy to source a 1-2mm spacer from a LBS.

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