From a posting by Bill to Hobbes back in 1994, this was Bill's first mention of 160mm rear spacing on the list:
Originally Posted by RickinFl
WHY DID SANTANA CHOOSE 160mm?
DISHED vs. DISHLESS. Maybe some engineer out there can determine the exact
percentage difference, but in our experience dishless wheels (where all the
spokes have the same load) are nearly twice as durable as standard dished
wheels (where half the spokes carry a majority of the load).
WIDE BRACING ANGLES. Further, if the hub is dishless, moving the flanges
further apart provides an improved bracing angle (the primary reason 26"
wheels are stronger than otherwise identical 700c wheels).
MORE COGS. Back in the mid-70s, when over 99% of all "ten speeds" featured
5-speed freewheels and 120mm spacing, Santana asked Phil Wood to produce
symmetric (dishless) hubs with a wider space between the flanges. These hubs,
the first built with 140mm spacing, became standard equipment on Santana's
original tandems-and other tandem builders soon followed Santana's lead. A
few years later, when the first tandem-strength 6-speed freewheels became
available (also at Santana's request), we moved the hub flanges closer
together. The resulting 6-speed wheels were weaker, yet still adequate. A few
years after that, 7-speed freewheels became available and, to obtain the
necessary additional clearance, we filed away part of the right chainstay and
re-introduced a "smidgen" of dish. The resulting 7-speed wheels (and the
frame), were weaker, but still adequate for most riders.
In the meantime, single bike spacing evolved from 120mm to 126mm to 130mm to
Three years ago customers started requesting eight cogs. And while it is not
impossible to shoehorn an extra cog into a 140mm tandem frame, the resulting
dished wheels will be considerably weaker (no matter who builds the hubs or
how many spokes are used).
Why 160? We could have made an incremental change to 150mm, but 160mm is the
minimum spacing that gets us back to our original uncompromised design;
completely dishless wheels, increased bracing angles, and unimpaired
chainstays. Within two or three years a majority of tandems will be built to
our new standard-it's the best way to combine reliability with today's
For those who would like to read more about the origin, rationale, and expections for 160mm rear hubs, this is a link to a 1996 post by Bill where he gets into all of the details some 2 years after the first posting in '94: http://search.bikelist.org/getmsg.as....9604.0451.eml