BB/crank selection on unorthodox build
hi guys, I'm looking for some help. I'm building a nice bike, and I'll post pictures when I'm done, but I need a bit of help choosing BB length/type and crank. I'll present what I know of my problem, and you guys can tell me where I'm wrong/need advice.
It's a Surly Karate Monkey, which is going to be set up fixed gear with bullhorns and Big Apple 28x2.35 tires. [Montreal has bad roads ] I've already worked out the geometry and bought some parts and the frame, now I'm getting into the drivetrain.
I think I want 144mm cranks, since that way there is a huge selection of chainrings in the 1/8" that I can choose from. Problem is, track cranks give chainlines around 42mm with 103mm spindle length BB's, and my 135mm rear spacing gives me a chainline of 53.5mm... so I'd need a 125-127mm BB spindle length... Is that a problem? I considered a mountain crankset, but I don't like the 4 bolt chainrings and there's not much in the way of 1/8" non-ramped chainrings for those cranks.
Are there cranks other than track (144) cranks that would give me a more outwards chainline while still giving me good 1/8" track chainring selection?
Also I am confused about the difference between square bottom bracket crank holders, the ISIS ones and the JIS ones, and the Octalink. The ISIS and Octalink systems look a hell of a lot better than the square ones, are there any cranks that would work for me that use ISIS or Octalink?
I am aware of the Phil Wood and White Industries BB's that feature adjustable chainline, and that seems like a good thing to me. However, is a 125-127mm BB spindle length ridiculous? Will it look stupid on my frame and there'll be a ton of air space between my cranks and frame?
Thanks a lot
Also, what are those outboard bearing bottom brackets? I hear they are mega stiff... are there cranks for those that would work for fixed gear usage?
Last edited by stomppow; 08-17-08 at 07:06 PM.
What wheels are you using?
I think if you have something like a formula hub, the spacers don't effect the chainline?
I haven't chosen my wheels yet. But I'm thinking Surly 135mm fixed hub in the rear. I'd prefer to get the chainline right without having modify the dish of the wheels. (I will build them myself over the winter, but I want this build to be clean.)
The Surly hub with a Surly cog gives 53.5mm chainline. Other 135mm hubs seem to give 52mm I think?
Oh, I just looked at Sheldon's site. I guess Formula doesn't go to 135. What a mess. Sorry.
I'd skip the 144 requirement on the KM.
I'd go with a 110 BCD so you can use BMX rings, and there's and a huge amount of choices in bottom bracket spindles.
Oh yeah, the KM also has a 73mm Bottom bracket shell. Keep that in mind.
I keep seeing bottom brackets that say they are for 68/73 shells, how is that? I don't understand.
The only problem with the mr. whirly is that I'm worried about chainring selection... I'm not mountain biking, I'm riding on the street with a gear ratio of something like 50/20.
My question is what is wrong with going 144 on the Karate Monkey? Is it just that it's hard to find 125mm BB spindle lengths? Or is it that putting a 125 or 127 mm long BB on a bike with track cranks will look mega stupid and be prone to breakage?
go with mtb cranks than you'll be able to throw an appropriate chainring on for riding it offroad.
68/73 bbs have a little spacer for using them with 68mm shells.
I already have a mountain bike, a 6"/6" suspension one. This Karate Monkey is going to romp the streets, hence the 50 tooth 1/8" chainring requirement.
I see that there are a few option in the 110 BCD for track chainrings, rarely 50 teeth, but it exists. Now, 130 BCD looks like a good compromise, and this would probably be the size that would feature the most outboard bearing BB's, right? Will I be able to find BB's that are long enough in this size?
What is the average chainline of 130 cranks?
Okay so I guess 5 arm mountain bike standard is 110, and that gives a pretty close chainline. But the 110 size doesn't give too many options for chainrings/outboard BB's? Also they're triples so I have a useless inner bolt pattern.
I'm leaning towards either road double 130 or road double 135. Does this look about right? The chainline is more outwards so I won't need as ridiculous a bottom bracket, plus I can use outboard bearing BB's?
Last edited by stomppow; 08-18-08 at 10:56 AM.
Okay after some more research, I'm heavily leaning towards either external bearing ISIS or external bearing Octalink bottom brackets, mated to road double 130 cranks.
So what I need to find is oversized (73mm) exteral bearing bottom brackets that are long enough in their spindles to get the chainline far enough out. Will I have problems?
Should I just go for track 144 and a really long internal bearing bottom bracket with square cranks?
Or hmm, the Truvativ Omnium 144 cranks could work with a 130mm long ISIS external BB. But all Truvativ makes is 128 so I'm 1mm of chainline off.
Also, I'm confused, I have english threading, but somehow in the truvativ manuals some BB's threading are described as 73E and some just as 73. Is the 73 Italian or something?
if you want 73mm external bearing you're going to have have to go with mtb. good thing it was the best option anyway.
Omniums and most other external bearing cranksets are two piece with the spindle attached to the spider and arm.
110 is not mtb standard but compact road. There are plenty of external options for it.
73 is new mtb standard allowing room for the derailer to mount on the bbshell for frames with now st.
Last edited by dutret; 08-18-08 at 01:23 PM.
Hmm, so if I were to get an Omnium, I would be stuck with whatever BB it came with (105mm length) and I wouldn't be able to detach the cranks to switch them onto a 128mm bb?
Okay so I guess mountain it is. But, what happens with the space in the BB for the derailleur attachment which I won't have, a spacer I guess?
Also, the chainline measurement that mountain cranks will give, is that for the middle chainring? What should I add to that to get the outside chainring which is where I'll attach a 1/8" one?
Last edited by stomppow; 08-18-08 at 04:27 PM.
sort of. The spindle is part of the cranks so you can't change that. The bb itself is just two bearing cartridges in cups to connect them to the bike. You would be able to put it in quite easily but once in the bearings would be too far apart to install the crank.
Originally Posted by stomppow
mtb BBs are spaced to make up for bb shells that are too small not vice versa.
Originally Posted by stomppow
see sheldon for chainline specifics. I would probably just run the ring on the inside with a guard.
I can't seem to find any 5 arm mountain cranksets... Are they old school? What's their spacing for chainrings?
I don't think I'm going to run a bash guard, this is for an urban bike when I'm in the city.
Maybe I should just get square track cranks and a long bb with the JIS square crank attachments.
Last edited by stomppow; 08-18-08 at 04:51 PM.
I think I found one other option, an ISIS outboard option:
Am I correct in thinking that I can buy the 128mm spindle ISIS bb in here http://www.sram.com/_media/techdocs/...aPipe-e-r2.pdf
and mate it to an ISIS crank like this