Yet Another Cycling Forum

General Category => The Knowledge => Topic started by: Jakob W on 12 July, 2020, 05:36:15 pm

Title: Spoke length and ERD measurement
Post by: Jakob W on 12 July, 2020, 05:36:15 pm

I've now got the rim for my first wheelbuilding attempt, and have a couple of questions about accurate ERD measurement:

1) should the threaded end of the spoke be level with the bottom or the middle of the nipple slot? I've seen either suggested, but the middle would seem to make sense from a wiggle room perspective.

2) Spoke lengths are nominally to the inside of the bend, aren't they? As I didn't have any spare spokes, I went to my friendly LBS and they handed me a couple that supposedly came from the 287mm box. Now, depending on which way I measure them, they're either 285.5mm (to the inside of the spoke bend), or 287mm (to the underside of the head). As a result, depending on how I place the jaws of my verniers, I get a 3mm difference in ERD. Or am I better off just trimming the spokes to a known length from the threaded end, and using a steel rule to measure the difference?

Title: Re: Spoke length and ERD measurement
Post by: Brucey on 12 July, 2020, 05:45:49 pm

1) middle is probably best, provided you are not using a single-wall rim.

(http://funicycle.com/magasin/images/d/commentMesurerLongueurRayonsDiametreConstant2mmHowToMesureSpokeRadiosSmall.jpg)

the above diagram is accurate (plenty are not).

cheers

Title: Re: Spoke length and ERD measurement
Post by: Jakob W on 12 July, 2020, 05:52:10 pm

Thanks - that means my measured ERD is 2mm more that the spec sheet, which I guess is near enough not to trigger immediate 'you must have mucked this up' errors. Will go back and double-check later.