Tandem Cycling - Mixing crank length

My wife runs 165 cranks on her single bike and I use 170's on mine. Our tandem has 170's and she is more comfortable with the shorter cranks. Is there any reason we should not have different lengths between captain and stoker cranks? (Assuming we can get 165mm cranks...)

None whatsoever. Many tandems are sold with mixed length cranks as standard equipment, albeit 175 / 170 which are probably too long for most teams who buy small or medium sized tandems.

165's are available from a few different sources:
- http://daVincitandems.com/ but they are fairly expensive.
- TA Specialities through http://PeterWhiteCycles.com/
- Thorn via http://SJSCycles.com/ in the UK
- Not sure if he still has any, but very affordable Dimension cranks via http://www.gtgtandems.com
- Check with the other tandem dealers: tandemseast.com, precisiontandems.com, bike123.com (Mt.Airy)
- Any LBS that has the full QBP catalog should be able to order the Dimension cranks if they are still available.

Crank length can be an issue. Yes 165s are available. Yes, crankarm lenghts can, and often are, of different lengths on tandems.
Stoker Kay, at just under 4'11" has always used 170s, although 165s are probably recommended. No complaints from her, so why worry/change?
On the other end of the spectrum did design a tandem for a duo: 6'7" and 5'2" and ended up with custom built 220mm crankarms for the tall dude!
Pedal on TWOgether!
Rudy and Kay/zonatandem

Thanks for the info. Fortunately we don't have such an extreme problem. We've decided not to change anything until after we finish the Seattle to Portland in two weeks.