Re: Thinking of changing crank 165m to 175mm

On 2/20/2025 4:39 AM, Catrike Ryder wrote:

On Wed, 19 Feb 2025 19:28:04 -0600, AMuzi <am@yellowjersey.org> wrote:
 

On 2/19/2025 5:47 PM, Catrike Ryder wrote:

>
I found a lightly used set of 175mm crank arms capable of taking a 5
bolt 130mm triple.
>
The seller says they have a ISIS BB interface.  My current crankset is
Sram Hollowcore so I'll need a new Bottom Bracket. My current BB is a
Sram Truvita Team GXP English. I had no trouble changing out the worn
out OEM Sram GXP BSA 10-4, but I'm at a loss on how to select the
correct ISIS BB.
>
Any help will be appreciated.
>
--
C'est bon
Soloman

>
Check out the crank manufacturer's page on that product for
recommended spindle length.

 I couldn't find anything about a cartridge BB specifically on a
Catrike.
 My confusion was establishing the proper overall cartridge length from
my shell width, which is 68mm. I see 68 x 108, 68X113, 68X118. It
seems to me that the differences will only involve the chainline,
which shouldn't matter too much because my chainlines run through
idlers, but still I want to minimize chain deflection. Sheldon's
website solved the problem for me. Triples and singles use the 113s.
--
C'est bon
Soloman

Sorry I meant crank manufacturer, not frame.
The general rule for crank bearings is, 'Thread matches frame, spindle length matches crank.'
Older cranks have a straight outer face and use spindles with a longer right side, that dimension varying by where the chainrings sit in relation to the crank arm mount.  The variants are mind-numbingly numerous and complex:
https://www.yellowjersey.org/photosfromthepast/CABB1986.JPG
Modern cranks (which includes ISIS and Octalink) from roughly 1990 on curve from pedal seat to crank mount:
http://www.yellowjersey.org/photosfromthepast/curve.jpg
which makes shorter spindles possible along with L-R spindle symmetry and dramatically fewer spindle formats.
For all spindles, new or old, consult crank manufacturer's recommended spindle dimensions.  There are often two lengths listed, for 42mm or 45mm chainline usually, either of which is fine for your very long chain runs.
--
Andrew Muzi
am@yellowjersey.org
Open every day since 1 April, 1971