On Dec 5, 1:01*pm, Chalo wrote:
DirtRoadie wrote:

I don't know the model designations nor dates of origin but my old
parts repository contained a 28T steel BP ring and the aforementioned
aluminum 26T. I don't believe the 26T is an "HP" version.

The major axis is nearly identical between the two, while it is the
26T which has a minor axis that matches a 24T (~81mm) as you describe.
The 28T is noticeably more round/oval (100/92mm) while the 26T at
98/82mm is also almost angular in appearance, somewhat like a
parallelogram *with rounded corners.

The overall roundness of the 28T ring counters my prior generalization
that smaller BP rings are less round.

There are obviously several flavors of BioPace.

I guess that's true, but up until now I had only distinguished the
original Biopace from Biopace HP, which was closer to round. *The
original triples were 48-38-28 only, because the 28t and 38t rings
could not be made smaller at that shape and still fit on a 110/74mm
spider.

I believe that the 26T ring I have was standard issue with a Deore XT
crank circa 1988.

The HP rings being rounder reminds me .....
Heck, no point in my re-writing it:

http://groups.google.com/group/rec.b...a35d362e155a3f

DR