Join Date: Dec 2005
Location: London, UK
Bikes: Trek T200 plus enough others to fill a large shed
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Good that you ask the question, since measuring a tandem is a bit different to a single bike.
I am 5'9" and have a medium T2000 from 2005, which is OK standover wise if a little higher than my normal bike. Length wise I ride a 54.6cm top tubed single bike with a 74 degree seat tube angle and 12 cm stem. On the tandem the top tube measures up as a 56, but in reality is more like a 55 since the eccentric rotates fwd to tension the timing chain so I could run a no-layback seatpost on the tandem whereas on my single bike I can't.
Second thing to think about is that the fork on the Trek is longer than on a single race bike, meaning you need to take this as well as headset and steerer length into account when checking the bar height. Basically I could get my finger between a 28mm tyre and the bottom of the fork, then the fork crown itself is big, meaning it's overall about 2cm longer than a road racing fork.
I ended up with an imperfect fit; main issue being the bars were about 2cm higher than I like. It was OK for a year since I don't race the tandem, then began to niggle, so I have just installed an Alpha Q X2 tandem fork, which is only a bit longer than a racing bike fork, which gets the bars in exactly the right position and allows use of a short drop caliper brake. I will report back on the handling once we've been for a decent ride.
Regarding the adjustable stoker stem, I don't like it either. I quickly ditched it as you could use it to moor a small boat. Since it uses a shim to attach to the captain's seat post, you can substitute it for a standard a-head stem, which saves a lot of weight and looks more elegant. Given your stoker is 5'2" you'll probably need a super-long stem of more than 14cm, so you may need to use the adjustable for a while until you can source one.
Overall I think the best approach is to make a scale drawing. Use the Trek geometry chart on their website to draw out the Trek frame starting from ground level, then pencil in the bottom brackets and wheel hubs, tyre radii and work upwards to draw in the centre lines of the steerer, seat tubes and top of the top tube and top of the seat tube clamps. Then measure your single bike and transfer the dimensions of your saddle height and setback and drop to handlebars to your scale drawing. With a few estimates or use of google for things like headset stack height you should be able to see reasonably accurately whether the postions will work.