Hi

At a race recently I saw a Tandem with a "shark tooth" fitted. It is a device made out of plastic that fits on the saddle downtube and stops the chain from being dropped to the inside of the chainwheels. The tandem has an 34,9 mm downtube.

Thanx in advance

Big H

I use a gizmo called a "third eye chain watcher." Retail cost is about $10.00. Shouldn't be very hard to find. Some LBS carry them in stock, I think that I've seen them in Nashbar and Performance catalogues too.

Although we don't use one, if we did it would be this one:
http://www.gvtc.com/~ngear/

Rich Shapiro sells them about as cheap as anyone else I've ever seen.
http://www.gtgtandems.com/parts/guides.html

Of course, other tandem speciality dealers carry them as well and you'll find them elsewhere, e.g., catalogs, etailers, etc...

Third Eye performs the same function, but uses a "one-size-fits-all" design with a hose clamp that nests inside the one-piece plastic chain guide.
http://www.excelsports.com/new.asp?page=8&description=Chain+Watcher&vendorCode=Thirdeye&major=6&minor=8

so cool, i wish it'd fit on my regular bike.