Tandem size question 5' 9" captain and stoker

[yes]

Hey all -
My girlfriend and I borrowed a tandem and put about 50 miles on it so far. We need to ride it some more this week, before returning it. Anyway - we're having a blast so far, and I've been perusing the classifieds and manufacturers web sites this week looking to see what is available.
We're both 5' 9". We generally can ride each others bikes without changing settings, so we're a very close match size wise. I ride a 55cm road bike, and she seems to fit fine on that, although she generally prefers a slightly shorter reach.
So, here's the question: Will we need to find a tandem with a longer stoker top tube, or will mediums generally fit us pretty well? I've looked at a few tandems with captain top tubes around 55cm. The stoker top tubes seemed to range from about 68cm to 72cm. Assuming a 10cm stem in the front, and trying to achieve the correct reach for her, then the 68cm top tube would require a stoker stem of only 3cm. Will that be possible? Would that put her too close?
Thanks for the help.

[TandemGeek]

http://www.nbc.com/The_Tonight_Show_with_Jay_Leno/headlines/H_2648/H_2648_32.jpg

A perfect fit...

Here's the deal, you have a tandem that you are test riding. Trade places and see how comfortable you could be with your bars sitting 3cm back from your GF's seatpost. Now, forget it's your girlfriend and instead it's your smelly posterior that's sitting a few inches under your nose on a long hot century.

To comfortably replicate your riding position you'll need a Rodriguez with a 30" stoker compartment or a custom job. Short of that, your best bet is a Co-Motion or a Trek which have ~28.5 stoker compartments on their Small & Medium-size models.

[yes]

That's pretty funny. Here's the odd thing. The one that we are testing out is 57cm tt up front and 70cm top tube in the back. Her bullhorns are on a pretty long adjustable stem - doh i didn't measure, but maybe 11cm. She says that there is plenty of room back there. I'm guessing that she is sitting upright. Oh, I've asked to have her drive, but she hasn't taken me up on it yet. There's always tomorrow - maybe she'll say yes.
Thanks for the tip on Rodriguez. Their web site is funny. Lots of opinions on steel, campy, and cantilever brakes, but nothing on why the long rear top tube. Oh, well.

[TandemGeek]

Lots of opinions on steel, campy, and cantilever brakes, but nothing on why the long rear top tube.

If you search the archives using terms like "stoker compartment" or "stoker top tube length" and my user ID you'll find a number of threads that discuss the pros and cons of long stoker compartments, etc...

This is a more recent one: http://www.bikeforums.net/showpost.php?p=4169650&postcount=18

Some of the literature you'll find on tandem design (usually highly biased marketing data for the most part) and the accompanying spiel used by some dealers will suggest that 27.75" or 28" stoker compartments can be made up to 30" long by shoving the stoker's saddle all the way back on an off-set seatpost coupled with bullhorns and a very short stem. The obvious flaws with these suggestions are that they ignore what the stoker's proper saddle set-back "should be" and also assume that the stoker doesn't mind planting their face in the back of their captain when using the "horns" or having the flats of their bars much closer than they would be on their 1/2 bike. In other words, it perpetuates the problems encountered by average or larger than average height stokers with well-developed road riding positions that can't be replicated on most stock production tandems.