# Thread: Optimal BB length for chainline???

1. ## Optimal BB length for chainline???

My new rear wheel uses a White Ind hub (not the eccentric version) - I need a new bottom bracket - What BB spindle width will provide the best chainline ???
I have a chainstay length of about 16.8 and I use a Truvativ crank with a 32 ring mounted on the inboard side of the spider.
Thanks all

2. What kind of frame? I use a White Ind hub as well and it is set to line up with the middle chainring on a triple crankset. In my particular case my GF uses a 73X113 for geared use. It would be the same bb length for the White Ind Hub. I guess you could measure it, but I would contact frame manuf. and ask what they recommend with that crank. Hope that makes sense.

3. Chainline has nothing to do with the frame, unless the frame is bent or has an offset rear triangle. It's got to do with the hub, BB spindle length and crankset. You pick the spindle length based on the crankset and hub. The only consideration you give to the frame is in making sure the chainring will clear the chainstay.

4. ## that's the problem

The only consideration you give to the frame is in making sure the chainring will clear the chainstay........

That's the problem - I had new wider chainstays put on the frame and I need a wider BB spindle length to have my chainring clear the chainstay, but want to keep a good chainline. Again - any experience with truvativ SS cranks (and suggested BB spindle lengths with a White Hub?)

5. The White Ind hub has a 47.5mm chainline, according to Lynette at WI. So:

Measure the distance from the seat tube to the center of your current chain ring. (x)
Measure the diameter of your seat tube. (y)
x + (y/2) = current crank chainline.
Subtract 47.5 from your current crank chainline.
If the result is negative, increase BB width by twice the result.
If the result is positive, decrease BB width by twice the result.
Take off cranks, measure BB width.
Buy the closest size BB to the calculated size.

Example:
Seat tube to chain ring = 30mm
Seat tube diameter = 31.8mm
Chain line = 30 + 15.9 = 45.9mm
45.9 - 47.5 = -1.6mm offset
Current BB width = 121mm
You need a 124.2mm BB, get the closest size you can find.

Will

6. The Truvativ manual lists the chainline you'll get for any given spindle length.

http://www.truvativ.com/manuals/2005/cr-4arm-e-r2.pdf or
http://www.truvativ.com/manuals/cr-4arm-e-r4.pdf

7. ## Thanks!

Just what I was looking for - Thanks so much - went and got a 115 today and presto - perfect clearance and only1.5 mm off my hub chainline. Should be ideal - have a great one

8. No problem. Out of curiosity, where did you get a 115? Who makes it?

9. ## Lbs

just went to lbs - its a good ol shimano un-73. You are correct in that Truvativ doesn't make one this size. Thanks to you I built the bike last night and its going on its first ride tonight.

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