Ok, my wife is about 5’7", and Im 5’11". She is looking to do some tris, mostly olympics and a few sprints possibly building to a 70.3 next year. Im a roadie who has been time trialing on my road bike with clipons. Mostly shorter <20 minute efforts. Is there anyway we could get away with using the same bike? I ride a 56 on the road, and she had a 54 road bike which we sold recently, but it was a touch big for her. I have read that a TT bike should sized down from your road bike (i.e. I would probably ride a 54 TT bike), but I don’t know how it works for triathletes trying to keep the hip angle open for running. Yes I am cheap and I do realize it would require saddle adjustments, and possibly a stem change for us to swap. Bad idea, or a REALLY STUPID ERASE THIS POST idea?
Sounds to me to be a colossal pain in the ass for a bike that most likely won’t fit either of you very well.
I’d say really bad idea but just below the erase this post line…
Good luck,
Travis
dumb blog
It is possible. It will not be ideal, but it could be done. Basically know the exact setup needed for both of you and see if you can find a frame that would bridge those differences with appropriate stem/seatpost etc.
The setup will almost certainly be suboptimized for one of you, if not both.
this would be a really easy question if it was for your identical twin.
It’s be really hard. If you were willing to ride slack, and she rode steep it may work but it depends on things like leg length, how much you’re willing to put up with and obviously cost is an issue.
Even things like housing will be less than ideal length if you’re moving the bars too much.
you can do this very easily. I’ve done this before out of laziness, when I tore my TT bike apart and didn’t want to put it back together. There’s a 5"-6" difference in height between me and Ms Roady, and I can easily ride her bike. Given the hassle of flying multiple bikes, if we do anything like fly to nationals, we’d just take on TT bike if our start times don’t overlap.
I would suggest an extra seatpost, just so you don’t have to mess with the setback/seat angle.
I can’t believe people get all worked up about bike sizing. She rides one size smaller than you do (maybe). It’s very easy to make a big one size bigger: raise the seat and, if needed, put on a little longer stem with some more rise. It’s not a big deal, regardless of what you read on the internet.
I’m two inches shorter than my husband, and there’s no way we could share bikes. Or at least not very comfortably. It’s not just the height difference, it’s the difference in our proportions–my legs are inches longer than his.
If I were your wife, I’d say, you do whatever you want…I’m off to buy my own bike. Wait…I DID say that 
Just say no…
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could work - depends on the fit triangles of the two riders. But I suspect that a pair of stems and pair of seatpost/saddles could make it happen.
g
Consider a Titanflex (yeah, I own one, I’m biased). Sliding the beam forward gives you a wide range of sizing (way more than saddle rails will allow). Put a Look Ergostem on it and you’ve got a good range of instant adjustability. This way either of you could ride shallow or steep. The guy who had my Titanflex before me (and rode it in the RAA) rode a 56cm, while I ride a 51cm, and the frame fits me dead on (no spacers though).
on one of my bike my g/f and i could ride it without doing more than adjusting the saddle about 1/4th of an inch, on the bikes we are on now we are both wildly different positions and there is no way it would work.