BB spindle length question?

[dustyrider]

Before a technical sub-forum opens up and my question gets lost in the abyss; What's the best way to determine your BB spindle length?

I'm thinking of running a white industries vbc on a bsa 68mm bike; 130mm rear spacing. Going to run a 11/36 10sp cassette and 48/32 rings. I was thinking the ole' 113 jis would be perfectly fine, but I started reading the white industries site about determining spindle length for these cranks.... Well I'm not a numbers type of person, and I already did my taxes, so any help from you bike geniuses?

[tuscanyswe]

Chainline shouldn't be a problem but perhaps the inner chainring could be depending on your chain stays width and how many tooth you are going for.

Edit: doubt a 32 would cause any problems..
http://0101.nccdn.net/1_5/30d/138/249/VBC_INNER_CHAIN_RING_CLEARANCES.pdf

[dustyrider]

Chainline shouldn't be a problem but perhaps the inner chainring could be depending on your chain stays width and how many tooth you are going for.

http://0101.nccdn.net/1_5/30d/138/249/VBC_INNER_CHAIN_RING_CLEARANCES.pdf

That's the document I'm reading and, I don't mind saying, unable to figure out. It's like a choose your own adventure book except I keep ending up at the beginning!

[Black Dog]

Usually the BB spindle length is set by the crank manufacturer for the width of BB that you will be installing the cranks onto. Contact WI and ask them what length they recommend and wether the tapers on the crank are ISO or JIS.

[tuscanyswe]

Well they are recommending a symmetrical JIS as in the document.

They are stating that a 113mm gives a chain line of 47.5 but that is measured to the outside ring. The inner ring sits at 38.3 something which gives the crank a pretty basic chain line of 42.9 with the 113mm bb when measured in the middle of the 2 chainrings as on usually does.

For comparisons sake a campy ut crank would have 43.5 measured this way, a .6mm difference.

The document is more about chain ring clearence to the chain stays of the inner ring. But you would have to have pretty beefy chain stays to not being able to fit a 32 tooth in the inner spot.

[Black Dog]

You should be very fine with a 113mm symmetrical JIS BB with that crank and ring combination. I read the document and you should enough clearance since the spacing gets better as you select smaller inner rings.

To be sure, measure back 67mm from the centre of the BB shell to the chain stays on both sides of the bike. Mark this point on each chain stay. Now measure the width of the outside of the two chain stays at the points that you marked. If it is less than 66.6mm you are golden to run anything less than a 38 tooth inner ring.