Find a Sutherland's catalog or borrow one, it has charts in the spoke lengths sections covering all the bead seat diameter / ERTO sizes - and their related marketing size. I'm pretty sure there's also a page in there on how to measure
bead set / ERTO diameter...
Or grab a chart online of the same. There are usually instruction on how to measure the actual rim in order to get the bead set or ERTO diameter.
I had to do this with a H-Plus-Son EERO a couple months back that turned out to
be a rim specifically aimed at "Terry" bikes. It was kinda weird but it happens...
You won't be able to do exact measurements...but you'll get within a millimeter
or so of what will be the most likely spec on a given chart.
=8-)
Robert Shackelford San Jose, CA USA
Quoting M-gineering <info@m-gineering.nl>:
> On 1/11/2011 6:19 PM, Eric Elman wrote:
> > Hello List Friends,
> >
> > I have three NOS Mavic Mod E rims that have no size markings on them. Can
> anyone advise what/where to measure (please be very specific) and the
> dimensions I should look for for in order to determine if they are 650b or
> 26"? They are not 700c just based on size comparison to numerous other 700c
> rims I have in my stash.
> >
> > Thanks in advance,
> >
> > Eric Elman
> > Somers, CT USA
> >
>
> Start with ETRTO sizing which is logical
>
> beaddiameter for a 650B tyre is 584mm, 650C = 571mm, 26" MTB is 559mm.
> With an inch at 25.4mm, it shouldn't be to difficult to keep them apart
>
>
> --
> mvg
>
> Marten Gerritsen
> Kiel Windeweer
> Netherlands