[gmac]

What is the "correct" lenght for a Bullit BB spindle ?

I'm running an old 118mm w/ an Evil DRS guide.

Seems to have messed the chainline up too much. So, I'm looking for the "correct" length. Also, after I get this #mm should I get a shorter BB due to the guide plate mounting under the lip of the BB (~3mm in width) ?

( I looked )

 

[Dartman]

I'm thinking about getting the RaceFace Signature DH BB in 118. It has an offset axle to accommodate chain guides. I have the Signature FR with a DH cup in 118 and the left side crank arm is very close to the swingarm.

Mike

 

[Wumpus]

Spindle length is dependent on type of cranks.

Chainline by Sheldon Brown -- He explains how to get the chainline by measuring the rear cassette.

Shimano cassettes are usually in the 47.5 range measured from the center of the seattube to the middle ring(3 rings) or between rings(2 rings).

Take the difference of your measurement and 47.5 and MULTIPLY by two. Add or subtract that number from your current spindle length and you have your optimum length.

I like to leave 3-4 mm between the crank and chainstay to account for any flex.

 

[tmmccree]

My brother has a 113mm SigFR bottom bracket (with the extra lipped ISIS cup) on his Bullit. He also uses a Blackspire chainguide, so his bottom bracket width is increased by approx 3mm. His bottom bracket is designed to work with either 68 or 73mm bottom brackets, so he has no problems at all. He is running NSXS cranks and has suitable clearance on both sides (cranks/swingarm), as well as a fairly decent chainline.

Personally, I'm not so well off so I'm running a Shimano UN52 square taper bottom bracket with Turbine LP cranks (also on a Bullit). My bottom bracket is a 118 x 73mm. I found I had to buy the extra shell length to fit the 68+3mm bottom bracket. It gives me decent crank/swingarm clearance, but really messed up my chainline. To solve this, I placed two washers between my chainring and cranks, thus spacing the chainring closer to the correct chainline.

Hope thats of some help.

Personally I wish 3mm was taken off the drive side of the bottom bracket shell, and a 3mm ring provided if people don't want to use a chainguide. This would allow a chainguide equiped bottom bracket to still have a 68mm width, so messed up chainlines wouldn't be such a problem.

 

[gmac]

I'm running the Shimano square UN52 113x68mm the RF Turbines & an EVIL DRS chainguide.

I figured the 113 length was plenty given the chainguide kind of extends the BB---> 3mm or so in length. John @ Evil said this is the setup he uses w/ his Bullit. The cranks clear nice and the chain & guide are working well.

Funny thing though, the LBS said I should run a wider BB w/ the chainguide. I tried to clarify that the BB would be pushed out by mounting the guide under the BB lip. The guy @ the shop said I still should use a longer BB (118). Didn't make sense to me. So, I ignored the advice. And went 113mm. Maybe he said this because he wanted the inner c-ring more outward so it would line up w/ the middle of the cluster ? Still it seemed excessive to me 5mm out.

Also, for knowledge sake: I don't get the 68 vs 73mm. I thought that indicated the shell diameter. But, it sounds like it means shell length is that correct ?

And for the Sheldon Brown link: thanks I'm saving that to my favs.