Are 9-speeds safe for tandems?

A posting from Bill at Santana

Three years ago engineers from Campagnolo, Shimano, Sachs and KMC all advised
Santana that the new 9-speed systems were not suitable for tandems (or even
single mountain bikes). They were right.

The problem? To stuff 9 cogs in frames originally designed for 7, Campagnolo
and Shimano specified a narrower chain with pin length reduced from 7.3mm to
only 6.6mm. This change required near-flush pins. While the new narrow chains
were just as strong for a straight pull, they could be pried apart twice as
easily during forced downshifts. The execs at KMC recalled a demonstration
where an overweight employee of a major US bike manufacturer performed a
forced downshift on a mountain bike while charging up a 20-foot high pile of
dirt ouside the back door of the factory. The guy pried apart 7 new chains
(various brands) in 7 attempts---a 100% failure rate on a test course only 50
feet long! Because road bike shifts are performed at high RPM with closely-
spaced cogs, the original 9-speed chains were only adequate for road bikes
with no more than a three-tooth spread between adjacent cogs. 

Within two years the 9-speed chains from Shimano, SRAM and KMC all featured a
"mushroomed pin" technology to help prevent pry-apart. Today's chains combine
carefully controlled pin and plate tempering with mushroomed pins, and are as
pry-resistant as tandem-proven 8-speed chains.

So everything's fine, right?

Yes, and no. Although the newest chains are strong enough for tandems,
customers need to take special care when installing or repairing these chains.

There are actually three broad generations of chain technology. I'll call
them: 

"pre-HG" == before the advent of ramped cogs
"HG" == today's 7/8 cog chain PLUS the original 9 speed chain
"HG-9" == today's 9 speed chain with mushroomed pins

The pre-HG chain used relatively loose pins that extended beyond the edge of
the outer plates. The loose-fitting pins were easy to install, and allowed
users to remove and replace pins for cleaning or splicing. Relatively idiot
proof.

The advent of HG (HyperGlide) ramped cogs created unanticipated chain pry-
apart problems. The chain makers responded with tight-pin technology. The
resulting chain was strong on the reel (chain is made in a continuous length),
but had a weak spot where the pin was pushed out for sizing and then re-
inserted during installation. Depending on the quality of the tool and
operator, the pry-apart strength of the spliced link was cut by no less than
10% (a trained operator using a pneumatic tool) to as much as 40% (an average
Joe with a hand-held chain tool). To help solve this problem Sachs, KMC and
Shimano developed special installation links. Trouble is, some people (even
bike shop mechanics) ignore these installation links and splice chains
together "the old fashioned way." The result, especially on tandems and
mountain bikes, is a high incidence of chain failure.

As if one weak spot created during installation wasn't bad enough, some
enthusiasts will "split" a chain to remove and clean it, and create a new weak
spot in the process. Or they'll install a larger cog or chainring and splice
in additional links (and two more weak spots). Still, because HG 7/8 speed
chains are strong enough for tandems and mountain bikes, on a single road bike
you can usually get away with haphazard chain splicing.

The newest 9-speed chains have deformed-at-the-end "mushroomed" pins. Because
up until now chain manufacturers have done a lousy job of telling people when
and why to use installation links (for fear their warning will cause you think
another brand of chain is superior), enthusiasts are bound to experience an
epidemic of failures with the newest 9-speed chains. Why? Because when you
drive out a mushroomed pin with your chain tool you will simultaneously
destroy the end of the pin while reaming the hole it was in. When you push the
shattered pin back into the enlarged hole, the resulting link has lost 70% of
its pry-apart strength.

Advice? Chain tools should only be used to push out the pieces of an outer
link, which should then be discarded. Use a KMC "Missing Link" to join
undamaged inner links. If you want to make a chain longer, you should use two
Missing Links. And if you want to be able to perform reliable enroute repairs,
you'll need a chain tool, Missing Links, and enough chain to replace a mangled
section.

Confused? Simply use a chain tool to break a chain and Missing Links to rejoin
it! If you don't have Missing Links and use a chain tool to effect an
emergency repair, shift gently on your way home and replace the chain before
your next ride.

Bill McCready
Santana Cycles, Inc
909/ 596-7570 x-11